https://www.electronicdesign.com/sponsored/video/55394933/quickchat-why-reed-relays-still-matter-in-modern-electronic-design
Does anyone here use reed relays? I recall them being nasty, noisy,
big, expensive, and unreliable.
https://www.electronicdesign.com/sponsored/video/55394933/quickchat-why-reed-relays-still-matter-in-modern-electronic-design
Does anyone here use reed relays? I recall them being nasty, noisy,
big, expensive, and unreliable.
john larkin <jl@htigct.com> wrote:
https://www.electronicdesign.com/sponsored/video/55394933/quickchat-why-reed-relays-still-matter-in-modern-electronic-design
Does anyone here use reed relays? I recall them being nasty, noisy,
big, expensive, and unreliable.
The main reason I havenrCOt used reeds is poor performance at low signal levels.
The ones IrCOve looked at had nylon cases (outside the glass envelope), so their leakage would be poor, and used different metals for the two
contacts, potentially leading to thermocouple offsets. So I went with
normal dry contact DIP relays, which had neither problem.
They also suck power, iirc, on account of a lousy magnetic circuit.
john larkin <jl@htigct.com> wrote:
https://www.electronicdesign.com/sponsored/video/55394933/quickchat-why-reed-relays-still-matter-in-modern-electronic-design
Does anyone here use reed relays? I recall them being nasty, noisy,
big, expensive, and unreliable.
The main reason I havenAt used reeds is poor performance at low signal >levels.
The ones IAve looked at had nylon cases (outside the glass envelope), so >their leakage would be poor, and used different metals for the two
contacts, potentially leading to thermocouple offsets. So I went with
normal dry contact DIP relays, which had neither problem.
They also suck power, iirc, on account of a lousy magnetic circuit.
Cheers
Phil Hobbs
john larkin <jl@htigct.com> wrote:
https://www.electronicdesign.com/sponsored/video/55394933/quickchat-why-reed-relays-still-matter-in-modern-electronic-design
Does anyone here use reed relays? I recall them being nasty, noisy,
big, expensive, and unreliable.
The main reason I havenrCOt used reeds is poor performance at low signal levels.
The ones IrCOve looked at had nylon cases (outside the glass envelope), so their leakage would be poor, and used different metals for the two
contacts, potentially leading to thermocouple offsets. So I went with
normal dry contact DIP relays, which had neither problem.
They also suck power, iirc, on account of a lousy magnetic circuit.
On Mon, 10 Aug 2026 22:13:42 -0000 (UTC), Phil Hobbs <pcdhSpamMeSenseless@electrooptical.net> wrote:
john larkin <jl@htigct.com> wrote:
https://www.electronicdesign.com/sponsored/video/55394933/quickchat-why-reed-relays-still-matter-in-modern-electronic-design
Does anyone here use reed relays? I recall them being nasty, noisy,
big, expensive, and unreliable.
The main reason I havenrCOt used reeds is poor performance at low signal
levels.
The ones IrCOve looked at had nylon cases (outside the glass envelope), so >> their leakage would be poor, and used different metals for the two
contacts, potentially leading to thermocouple offsets. So I went with
normal dry contact DIP relays, which had neither problem.
They also suck power, iirc, on account of a lousy magnetic circuit.
Cheers
Phil Hobbs
Yes, bad thermals. And they twang when they close, generate hundreds
of microvolts of complex ringing for many milliseconds.
Some have to be separated from their neighbors or they may not
release.
I did a data acquisition system with reeds and the twanging forced the
scan rate low.
I did a many-channel liquid helium level measurement system with reeds
to mux the sensors, with cold switching even [1], and failure rates
were high.
[1] no pun intended
Am 11.08.26 um 02:26 schrieb john larkin:
On Mon, 10 Aug 2026 22:13:42 -0000 (UTC), Phil Hobbs
<pcdhSpamMeSenseless@electrooptical.net> wrote:
john larkin <jl@htigct.com> wrote:
https://www.electronicdesign.com/sponsored/video/55394933/quickchat-why-reed-relays-still-matter-in-modern-electronic-design
Does anyone here use reed relays? I recall them being nasty, noisy,
big, expensive, and unreliable.
The main reason I havenrCOt used reeds is poor performance at low signal >>> levels.
The ones IrCOve looked at had nylon cases (outside the glass envelope), so >>> their leakage would be poor, and used different metals for the two
contacts, potentially leading to thermocouple offsets.-a So I went with
normal dry contact DIP relays, which had neither problem.
They also suck power, iirc, on account of a lousy magnetic circuit.
Cheers
Phil Hobbs
Yes, bad thermals. And they twang when they close, generate hundreds
of microvolts of complex ringing for many milliseconds.
Some have to be separated from their neighbors or they may not
release.
I did a data acquisition system with reeds and the twanging forced the
scan rate low.
I did a many-channel liquid helium level measurement system with reeds
to mux the sensors, with cold switching even [1], and failure rates
were high.
-a [1] no pun intended
I still have two or three trays of mercury-wetted reed relays.
I bought them as surplus when I still was a student. They'll go
to the problem waste on next opportunity.
https://www.electronicdesign.com/sponsored/video/55394933/quickchat-why-reed-relays-still-matter-in-modern-electronic-design
Does anyone here use reed relays? I recall them being nasty, noisy,
big, expensive, and unreliable.
On Mon, 10 Aug 2026 14:46:29 -0700, john larkin <jl@htigct.com> wrote:
https://www.electronicdesign.com/sponsored/video/55394933/quickchat-why-reed-relays-still-matter-in-modern-electronic-design
Does anyone here use reed relays? I recall them being nasty, noisy,
big, expensive, and unreliable.
Doesn't sound like John Larkin.
I thought you'd been using them in fairly large quantities
for a while now - posting about their density and proximity.
Seem to be doing their job on 20 channel multiplexing boards
in my venerable HP34970As for the last 30 years (they count
and record relay operations FYI). These are on replaceable
modules - almost exclusively supplied/refurbished in Malaysia.
I'm carefull around power node sensing - always at least 10R
in series with any sensing wires.
RL
<https://www.electronicdesign.com/sponsored/video/55394933/quickchat-why-reed-relays-still-matter-in-modern-electronic-design>
Does anyone here use reed relays? I recall them being nasty, noisy,
big, expensive, and unreliable.
On Mon, 10 Aug 2026 14:46:29 -0700, john larkin <jl@htigct.com> wrote:
<https://www.electronicdesign.com/sponsored/video/55394933/quickchat-why-reed-relays-still-matter-in-modern-electronic-design>
Does anyone here use reed relays? I recall them being nasty, noisy,
big, expensive, and unreliable.
I did use reed switches in their day. The key was to avoid gold
contacts, as they always stuck or even welded closed. The preferred
coating was Rhodium. Which is more expensive than Gold.
Joe
On Tue, 11 Aug 2026 09:15:06 -0400, legg <legg@nospam.magma.ca> wrote:
On Mon, 10 Aug 2026 14:46:29 -0700, john larkin <jl@htigct.com> wrote:
https://www.electronicdesign.com/sponsored/video/55394933/quickchat-why-reed-relays-still-matter-in-modern-electronic-design
Does anyone here use reed relays? I recall them being nasty, noisy,
big, expensive, and unreliable.
Doesn't sound like John Larkin.
I thought you'd been using them in fairly large quantities
for a while now - posting about their density and proximity.
Seem to be doing their job on 20 channel multiplexing boards
in my venerable HP34970As for the last 30 years (they count
and record relay operations FYI). These are on replaceable
modules - almost exclusively supplied/refurbished in Malaysia.
I'm carefull around power node sensing - always at least 10R
in series with any sensing wires.
RL
We use no reed relays. Never again!
On 12/08/2026 1:13 am, john larkin wrote:
On Tue, 11 Aug 2026 09:15:06 -0400, legg <legg@nospam.magma.ca> wrote:
On Mon, 10 Aug 2026 14:46:29 -0700, john larkin <jl@htigct.com> wrote:
https://www.electronicdesign.com/sponsored/video/55394933/quickchat-why-reed-relays-still-matter-in-modern-electronic-design
Does anyone here use reed relays? I recall them being nasty, noisy,
big, expensive, and unreliable.
Doesn't sound like John Larkin.
I thought you'd been using them in fairly large quantities
for a while now - posting about their density and proximity.
Seem to be doing their job on 20 channel multiplexing boards
in my venerable HP34970As for the last 30 years (they count
and record relay operations FYI). These are on replaceable
modules - almost exclusively supplied/refurbished in Malaysia.
I'm carefull around power node sensing - always at least 10R
in series with any sensing wires.
RL
We use no reed relays. Never again!
If you don't read the data sheets carefully you can make any component
misbehave.
<snipped the usual selection of other things John could persuade to work.>
On Wed, 12 Aug 2026 02:38:35 +1000, Bill Sloman <bill.sloman@ieee.org>
wrote:
On 12/08/2026 1:13 am, john larkin wrote:
On Tue, 11 Aug 2026 09:15:06 -0400, legg <legg@nospam.magma.ca> wrote:
On Mon, 10 Aug 2026 14:46:29 -0700, john larkin <jl@htigct.com> wrote: >>>>
https://www.electronicdesign.com/sponsored/video/55394933/quickchat-why-reed-relays-still-matter-in-modern-electronic-design
Does anyone here use reed relays? I recall them being nasty, noisy,
big, expensive, and unreliable.
Doesn't sound like John Larkin.
I thought you'd been using them in fairly large quantities
for a while now - posting about their density and proximity.
Seem to be doing their job on 20 channel multiplexing boards
in my venerable HP34970As for the last 30 years (they count
and record relay operations FYI). These are on replaceable
modules - almost exclusively supplied/refurbished in Malaysia.
I'm carefull around power node sensing - always at least 10R
in series with any sensing wires.
RL
We use no reed relays. Never again!
If you don't read the data sheets carefully you can make any component
misbehave.
The only problem we've seen with the Fujitsues is : don't water wash.
<snipped the usual selection of other things John could persuade to work.>
That's what engineering is: make things work.
On Tue, 11 Aug 2026 09:15:06 -0400, legg <legg@nospam.magma.ca> wrote:
On Mon, 10 Aug 2026 14:46:29 -0700, john larkin <jl@htigct.com> wrote:
https://www.electronicdesign.com/sponsored/video/55394933/quickchat-why-reed-relays-still-matter-in-modern-electronic-design
Does anyone here use reed relays? I recall them being nasty, noisy,
big, expensive, and unreliable.
Doesn't sound like John Larkin.
I thought you'd been using them in fairly large quantities
for a while now - posting about their density and proximity.
Seem to be doing their job on 20 channel multiplexing boards
in my venerable HP34970As for the last 30 years (they count
and record relay operations FYI). These are on replaceable
modules - almost exclusively supplied/refurbished in Malaysia.
I'm carefull around power node sensing - always at least 10R
in series with any sensing wires.
RL
We use no reed relays. Never again!
SSRs are our preferred single-pole switches, but real relays are
closer to ideal switches.
The Fujitsu FTR-B3GA series is wonderful. We've used over 100K so far.
It's a small, very well-behaved DPDT relay, good to 2 GHz or so, costs
$1 or so in quantity.
There's a latching version, no thermals.
https://www.dropbox.com/scl/fi/gxdx7d6g1pqy9qgz3jr57/DSC06884.JPG?rlkey=qg3pxra2sh7u4hm995je7kt75&raw=1
https://www.dropbox.com/scl/fi/xopma1w8ialt78fkdd5er/DSC06873.JPG?rlkey=tpmgxvmiq60jcnuj8gnmhwont&raw=1
On 12/08/2026 2:46 am, john larkin wrote:
On Wed, 12 Aug 2026 02:38:35 +1000, Bill Sloman <bill.sloman@ieee.org>
wrote:
On 12/08/2026 1:13 am, john larkin wrote:
On Tue, 11 Aug 2026 09:15:06 -0400, legg <legg@nospam.magma.ca> wrote: >>>>
On Mon, 10 Aug 2026 14:46:29 -0700, john larkin <jl@htigct.com> wrote: >>>>>
https://www.electronicdesign.com/sponsored/video/55394933/quickchat-why-reed-relays-still-matter-in-modern-electronic-design
Does anyone here use reed relays? I recall them being nasty, noisy, >>>>>> big, expensive, and unreliable.
Doesn't sound like John Larkin.
I thought you'd been using them in fairly large quantities
for a while now - posting about their density and proximity.
Seem to be doing their job on 20 channel multiplexing boards
in my venerable HP34970As for the last 30 years (they count
and record relay operations FYI). These are on replaceable
modules - almost exclusively supplied/refurbished in Malaysia.
I'm carefull around power node sensing - always at least 10R
in series with any sensing wires.
RL
We use no reed relays. Never again!
If you don't read the data sheets carefully you can make any component >>> misbehave.
The only problem we've seen with the Fujitsues is : don't water wash.
<snipped the usual selection of other things John could persuade to work.> >>That's what engineering is: make things work.
But if helps if you know how the components you put together are
designed to work. Data sheets tell you about that, if you read them >carefully and have the wit to understand what they are trying to tell you.
Sometimes it takes real ingenuity to put off-the-shelf stuff together to--- Synchronet 3.22a-Linux NewsLink 1.2
get it to do what you customer wants it to do. Sometimes you can even
patent the approach, though it can happen that several people can have
the same good idea at much the same time and only the one who filed
first gets the patent.
https://www.electronicdesign.com/sponsored/video/55394933/quickchat-why-reed-relays-still-matter-in-modern-electronic-design
Does anyone here use reed relays? I recall them being nasty, noisy,
big, expensive, and unreliable.
john larkin <jl@htigct.com> wrote:
On Tue, 11 Aug 2026 09:15:06 -0400, legg <legg@nospam.magma.ca> wrote:
On Mon, 10 Aug 2026 14:46:29 -0700, john larkin <jl@htigct.com> wrote:
https://www.electronicdesign.com/sponsored/video/55394933/quickchat-why-reed-relays-still-matter-in-modern-electronic-design
Does anyone here use reed relays? I recall them being nasty, noisy, >>>>big, expensive, and unreliable.
Doesn't sound like John Larkin.
I thought you'd been using them in fairly large quantities
for a while now - posting about their density and proximity.
Seem to be doing their job on 20 channel multiplexing boards
in my venerable HP34970As for the last 30 years (they count
and record relay operations FYI). These are on replaceable
modules - almost exclusively supplied/refurbished in Malaysia.
I'm carefull around power node sensing - always at least 10R
in series with any sensing wires.
RL
We use no reed relays. Never again!
SSRs are our preferred single-pole switches, but real relays are
closer to ideal switches.
The Fujitsu FTR-B3GA series is wonderful. We've used over 100K so far.
It's a small, very well-behaved DPDT relay, good to 2 GHz or so, costs
$1 or so in quantity.
There's a latching version, no thermals.
https://www.dropbox.com/scl/fi/gxdx7d6g1pqy9qgz3jr57/DSC06884.JPG?rlkey=qg3pxra2sh7u4hm995je7kt75&raw=1
https://www.dropbox.com/scl/fi/xopma1w8ialt78fkdd5er/DSC06873.JPG?rlkey=tpmgxvmiq60jcnuj8gnmhwont&raw=1
OK, those will have a HORRIBLE thermal-EMF. Might be OK for switching >something digital or RF but light years from COTO low thermal-EMF relays. >They are from a totally different domain, absolutely non-suitable for low >level signals where a DECENT (not even stellar) precision is needed.
Then, they have 1 GOhm insulation resistance which is 3 ORDERS OF MAGNITUDE >worse than low-thermal Cotos. Not TIMES worse but 3 ORDERS OF MAGNITUDE >worse.
General purpose relays like those Fujitsus can be replaced with something >non-mechanical in MOST (but not all) applications. And there are tons of >different ones from different manufacturers if you still need a RELAY -- >Fujitsu is not the only player in the field and it is not even unique or any >different from the others.--- Synchronet 3.22a-Linux NewsLink 1.2
For something like those low-thermal Cotos there is no replacement. Like it >or not but when you enter metrology (or nearby) land you won't have any
other choice. Sure enough it is not a heavily populated land with tons of >vegetation at every square inch of it but it still exists and inhabited by >very strange creatures.
---
******************************************************************
* KSI@home KOI8 Net < > The impossible we do immediately. *
* Las Vegas NV, USA < > Miracles require 24-hour notice. * >******************************************************************
john larkin <jl@htigct.com> wrote:
https://www.electronicdesign.com/sponsored/video/55394933/quickchat-why-reed-relays-still-matter-in-modern-electronic-design
Does anyone here use reed relays? I recall them being nasty, noisy,
big, expensive, and unreliable.
Had great experiences with pricier big name US and European brands and >terrible times with budget Asian brands, contacts sticking was always the >problem despite peak currents limited by resistance to <20mA at worst and >mostly microamps.
On Tue, 11 Aug 2026 20:30:49 -0000 (UTC), piglet
<erichpwagner@hotmail.com> wrote:
john larkin <jl@htigct.com> wrote:
https://www.electronicdesign.com/sponsored/video/55394933/quickchat-why-reed-relays-still-matter-in-modern-electronic-design
Does anyone here use reed relays? I recall them being nasty, noisy,
big, expensive, and unreliable.
Had great experiences with pricier big name US and European brands and
terrible times with budget Asian brands, contacts sticking was always the
problem despite peak currents limited by resistance to <20mA at worst and
mostly microamps.
Some will stick if left closed for a long time at zero current.
On Tue, 11 Aug 2026 20:01:48 -0000 (UTC), Sergey Kubushyn
<ksi@koi8.net> wrote:
john larkin <jl@htigct.com> wrote:
On Tue, 11 Aug 2026 09:15:06 -0400, legg <legg@nospam.magma.ca> wrote:
On Mon, 10 Aug 2026 14:46:29 -0700, john larkin <jl@htigct.com> wrote:
https://www.electronicdesign.com/sponsored/video/55394933/quickchat-why-reed-relays-still-matter-in-modern-electronic-design
Does anyone here use reed relays? I recall them being nasty, noisy, >>>>>big, expensive, and unreliable.
Doesn't sound like John Larkin.
I thought you'd been using them in fairly large quantities
for a while now - posting about their density and proximity.
Seem to be doing their job on 20 channel multiplexing boards
in my venerable HP34970As for the last 30 years (they count
and record relay operations FYI). These are on replaceable
modules - almost exclusively supplied/refurbished in Malaysia.
I'm carefull around power node sensing - always at least 10R
in series with any sensing wires.
RL
We use no reed relays. Never again!
SSRs are our preferred single-pole switches, but real relays are
closer to ideal switches.
The Fujitsu FTR-B3GA series is wonderful. We've used over 100K so far.
It's a small, very well-behaved DPDT relay, good to 2 GHz or so, costs
$1 or so in quantity.
There's a latching version, no thermals.
https://www.dropbox.com/scl/fi/gxdx7d6g1pqy9qgz3jr57/DSC06884.JPG?rlkey=qg3pxra2sh7u4hm995je7kt75&raw=1
https://www.dropbox.com/scl/fi/xopma1w8ialt78fkdd5er/DSC06873.JPG?rlkey=tpmgxvmiq60jcnuj8gnmhwont&raw=1
OK, those will have a HORRIBLE thermal-EMF. Might be OK for switching >>something digital or RF but light years from COTO low thermal-EMF relays. >>They are from a totally different domain, absolutely non-suitable for low >>level signals where a DECENT (not even stellar) precision is needed.
The standard version is only fair, but the latching version has about
zero thermals.
Then, they have 1 GOhm insulation resistance which is 3 ORDERS OF MAGNITUDE >>worse than low-thermal Cotos. Not TIMES worse but 3 ORDERS OF MAGNITUDE >>worse.
In real life they are better. They don't production test $1 relays for attoamp leakage.
I designed a test mux box using them.
https://www.dropbox.com/scl/fo/6nyerqdbdlno2k98ifjc5/AMmsFfmBte6cb6VW70UHvg8?rlkey=ngzczkb2vv5ho3gfbbqpj2l6i&dl=0
I think that's the biggest PCB that I've ever done.
With a fan in the 3U rackmount box, it multiplexes thermocouples OK. I
should have used the latching relays.
General purpose relays like those Fujitsus can be replaced with something >>non-mechanical in MOST (but not all) applications. And there are tons of >>different ones from different manufacturers if you still need a RELAY -- >>Fujitsu is not the only player in the field and it is not even unique or any >>different from the others.
For something like those low-thermal Cotos there is no replacement. Like it >>or not but when you enter metrology (or nearby) land you won't have any >>other choice. Sure enough it is not a heavily populated land with tons of >>vegetation at every square inch of it but it still exists and inhabited by >>very strange creatures.
john larkin <jl@htigct.com> wrote:
On Tue, 11 Aug 2026 20:01:48 -0000 (UTC), Sergey Kubushyn
<ksi@koi8.net> wrote:
john larkin <jl@htigct.com> wrote:
On Tue, 11 Aug 2026 09:15:06 -0400, legg <legg@nospam.magma.ca> wrote: >>>>
On Mon, 10 Aug 2026 14:46:29 -0700, john larkin <jl@htigct.com> wrote: >>>>>
https://www.electronicdesign.com/sponsored/video/55394933/quickchat-why-reed-relays-still-matter-in-modern-electronic-design
Does anyone here use reed relays? I recall them being nasty, noisy, >>>>>>big, expensive, and unreliable.
Doesn't sound like John Larkin.
I thought you'd been using them in fairly large quantities
for a while now - posting about their density and proximity.
Seem to be doing their job on 20 channel multiplexing boards
in my venerable HP34970As for the last 30 years (they count
and record relay operations FYI). These are on replaceable
modules - almost exclusively supplied/refurbished in Malaysia.
I'm carefull around power node sensing - always at least 10R
in series with any sensing wires.
RL
We use no reed relays. Never again!
SSRs are our preferred single-pole switches, but real relays are
closer to ideal switches.
The Fujitsu FTR-B3GA series is wonderful. We've used over 100K so far. >>>> It's a small, very well-behaved DPDT relay, good to 2 GHz or so, costs >>>> $1 or so in quantity.
There's a latching version, no thermals.
https://www.dropbox.com/scl/fi/gxdx7d6g1pqy9qgz3jr57/DSC06884.JPG?rlkey=qg3pxra2sh7u4hm995je7kt75&raw=1
https://www.dropbox.com/scl/fi/xopma1w8ialt78fkdd5er/DSC06873.JPG?rlkey=tpmgxvmiq60jcnuj8gnmhwont&raw=1
OK, those will have a HORRIBLE thermal-EMF. Might be OK for switching >>>something digital or RF but light years from COTO low thermal-EMF relays. >>>They are from a totally different domain, absolutely non-suitable for low >>>level signals where a DECENT (not even stellar) precision is needed.
The standard version is only fair, but the latching version has about
zero thermals.
Thermals come from the contacts and the connecting parts. Latching relays
are no different, just different mechanics.
Do they specify thermal EMF for those latching relays? Why would stupid >metrology grade instruments' designers use VERY expensive COTO reed relays >with whopping <0.5uV thermal EMF instead of those about zero thermal jewels >that cost $1 a bucketful?
Then, they have 1 GOhm insulation resistance which is 3 ORDERS OF MAGNITUDE >>>worse than low-thermal Cotos. Not TIMES worse but 3 ORDERS OF MAGNITUDE >>>worse.
In real life they are better. They don't production test $1 relays for
attoamp leakage.
Yeah, they just want to sell them as a cheap junk instead of charging at >least an order of magnitude more... And they don't know that, e.g., $1
Susumu resistors are much better in real life so they buy oil-filled VHP101 >and such from Vishay for $100+ apiece...
I designed a test mux box using them.
https://www.dropbox.com/scl/fo/6nyerqdbdlno2k98ifjc5/AMmsFfmBte6cb6VW70UHvg8?rlkey=ngzczkb2vv5ho3gfbbqpj2l6i&dl=0
I think that's the biggest PCB that I've ever done.
With a fan in the 3U rackmount box, it multiplexes thermocouples OK. I
should have used the latching relays.
Thermocouples are very crude devices, good to +/- 1 degree Celsius or such >for the low temperature ones. The high temperature ones are worse. They are >not anywhere near "precision".
A good Pt probe easily gets to .01 degree precision. A [limited range] >thermistor is even better, .001 degree is achievable. An old Hart/Fluke >Tweener 1504, e.g. has .003 degrees accuracy typical with .0001 degrees >resolution when used with a good probe. An SPRT sibling, 1502, has .006 >degrees accuracy with .001 degree resolution. Those are OLD instruments.
Kaye all-in-one (you only provide power and talk over RS-232 with it) >IRTD-400 has a range of -196 to 420 degrees Celsius and has a guaranteed >accuracy of .025 degrees over ENTIRE range with .001 degree resolution. Much >better farther from extremes.
This is where all those fancy components are used. For a stupid
thermocouples with "cold/warm/hot/too hot" measurements [almost] ANY signal >relay is OK.
--- Synchronet 3.22a-Linux NewsLink 1.2General purpose relays like those Fujitsus can be replaced with something >>>non-mechanical in MOST (but not all) applications. And there are tons of >>>different ones from different manufacturers if you still need a RELAY -- >>>Fujitsu is not the only player in the field and it is not even unique or any >>>different from the others.
For something like those low-thermal Cotos there is no replacement. Like it >>>or not but when you enter metrology (or nearby) land you won't have any >>>other choice. Sure enough it is not a heavily populated land with tons of >>>vegetation at every square inch of it but it still exists and inhabited by >>>very strange creatures.
---
******************************************************************
* KSI@home KOI8 Net < > The impossible we do immediately. *
* Las Vegas NV, USA < > Miracles require 24-hour notice. * >******************************************************************
On 11/08/2026 22:59, john larkin wrote:
On Tue, 11 Aug 2026 20:30:49 -0000 (UTC), piglet
<erichpwagner@hotmail.com> wrote:
john larkin <jl@htigct.com> wrote:
https://www.electronicdesign.com/sponsored/video/55394933/quickchat-why-reed-relays-still-matter-in-modern-electronic-design
Does anyone here use reed relays? I recall them being nasty, noisy,
big, expensive, and unreliable.
Had great experiences with pricier big name US and European brands and
terrible times with budget Asian brands, contacts sticking was always the >>> problem despite peak currents limited by resistance to <20mA at worst and >>> mostly microamps.
Some will stick if left closed for a long time at zero current.
Or go high resistance. Many relays have a minimum current - AKA
as the "wetting current".
John
On Wed, 12 Aug 2026 03:18:44 +1000, Bill Sloman <bill.sloman@ieee.org>
wrote:
On 12/08/2026 2:46 am, john larkin wrote:
On Wed, 12 Aug 2026 02:38:35 +1000, Bill Sloman <bill.sloman@ieee.org>
wrote:
On 12/08/2026 1:13 am, john larkin wrote:
On Tue, 11 Aug 2026 09:15:06 -0400, legg <legg@nospam.magma.ca> wrote: >>>>>
On Mon, 10 Aug 2026 14:46:29 -0700, john larkin <jl@htigct.com> wrote: >>>>>>
https://www.electronicdesign.com/sponsored/video/55394933/quickchat-why-reed-relays-still-matter-in-modern-electronic-design
Does anyone here use reed relays? I recall them being nasty, noisy, >>>>>>> big, expensive, and unreliable.
Doesn't sound like John Larkin.
I thought you'd been using them in fairly large quantities
for a while now - posting about their density and proximity.
Seem to be doing their job on 20 channel multiplexing boards
in my venerable HP34970As for the last 30 years (they count
and record relay operations FYI). These are on replaceable
modules - almost exclusively supplied/refurbished in Malaysia.
I'm carefull around power node sensing - always at least 10R
in series with any sensing wires.
RL
We use no reed relays. Never again!
If you don't read the data sheets carefully you can make any component >>>> misbehave.
The only problem we've seen with the Fujitsues is : don't water wash.
<snipped the usual selection of other things John could persuade to work.> >>>That's what engineering is: make things work.
But if helps if you know how the components you put together are
designed to work. Data sheets tell you about that, if you read them
carefully and have the wit to understand what they are trying to tell you.
And if you trust them, which I suggest you don't do absolutely. When
in doubt, test.
Sometimes it takes real ingenuity to put off-the-shelf stuff together to
get it to do what you customer wants it to do. Sometimes you can even
patent the approach, though it can happen that several people can have
the same good idea at much the same time and only the one who filed
first gets the patent.
john larkin <jl@htigct.com> wrote:
On Tue, 11 Aug 2026 20:01:48 -0000 (UTC), Sergey Kubushyn
<ksi@koi8.net> wrote:
john larkin <jl@htigct.com> wrote:
On Tue, 11 Aug 2026 09:15:06 -0400, legg <legg@nospam.magma.ca> wrote: >>>>
On Mon, 10 Aug 2026 14:46:29 -0700, john larkin <jl@htigct.com> wrote: >>>>>
https://www.electronicdesign.com/sponsored/video/55394933/quickchat-why-reed-relays-still-matter-in-modern-electronic-design
Does anyone here use reed relays? I recall them being nasty, noisy, >>>>>> big, expensive, and unreliable.
Doesn't sound like John Larkin.
I thought you'd been using them in fairly large quantities
for a while now - posting about their density and proximity.
Seem to be doing their job on 20 channel multiplexing boards
in my venerable HP34970As for the last 30 years (they count
and record relay operations FYI). These are on replaceable
modules - almost exclusively supplied/refurbished in Malaysia.
I'm carefull around power node sensing - always at least 10R
in series with any sensing wires.
RL
We use no reed relays. Never again!
SSRs are our preferred single-pole switches, but real relays are
closer to ideal switches.
The Fujitsu FTR-B3GA series is wonderful. We've used over 100K so far. >>>> It's a small, very well-behaved DPDT relay, good to 2 GHz or so, costs >>>> $1 or so in quantity.
There's a latching version, no thermals.
https://www.dropbox.com/scl/fi/gxdx7d6g1pqy9qgz3jr57/DSC06884.JPG?rlkey=qg3pxra2sh7u4hm995je7kt75&raw=1
https://www.dropbox.com/scl/fi/xopma1w8ialt78fkdd5er/DSC06873.JPG?rlkey=tpmgxvmiq60jcnuj8gnmhwont&raw=1
OK, those will have a HORRIBLE thermal-EMF. Might be OK for switching
something digital or RF but light years from COTO low thermal-EMF relays. >>> They are from a totally different domain, absolutely non-suitable for low >>> level signals where a DECENT (not even stellar) precision is needed.
The standard version is only fair, but the latching version has about
zero thermals.
Thermals come from the contacts and the connecting parts. Latching relays
are no different, just different mechanics.
Do they specify thermal EMF for those latching relays? Why would stupid metrology grade instruments' designers use VERY expensive COTO reed relays with whopping <0.5uV thermal EMF instead of those about zero thermal jewels that cost $1 a bucketful?
Then, they have 1 GOhm insulation resistance which is 3 ORDERS OF MAGNITUDE >>> worse than low-thermal Cotos. Not TIMES worse but 3 ORDERS OF MAGNITUDE
worse.
In real life they are better. They don't production test $1 relays for
attoamp leakage.
Yeah, they just want to sell them as a cheap junk instead of charging at least an order of magnitude more... And they don't know that, e.g., $1
Susumu resistors are much better in real life so they buy oil-filled VHP101 and such from Vishay for $100+ apiece...
I designed a test mux box using them.
https://www.dropbox.com/scl/fo/6nyerqdbdlno2k98ifjc5/AMmsFfmBte6cb6VW70UHvg8?rlkey=ngzczkb2vv5ho3gfbbqpj2l6i&dl=0
I think that's the biggest PCB that I've ever done.
With a fan in the 3U rackmount box, it multiplexes thermocouples OK. I
should have used the latching relays.
Thermocouples are very crude devices, good to +/- 1 degree Celsius or such for the low temperature ones. The high temperature ones are worse. They are not anywhere near "precision".
A good Pt probe easily gets to .01 degree precision. A [limited range] thermistor is even better, .001 degree is achievable.
An old Hart/Fluke
Tweener 1504, e.g. has .003 degrees accuracy typical with .0001 degrees resolution when used with a good probe. An SPRT sibling, 1502, has .006 degrees accuracy with .001 degree resolution. Those are OLD instruments.
Kaye all-in-one (you only provide power and talk over RS-232 with it) IRTD-400 has a range of -196 to 420 degrees Celsius and has a guaranteed accuracy of .025 degrees over ENTIRE range with .001 degree resolution. Much better farther from extremes.
This is where all those fancy components are used. For a stupid
thermocouples with "cold/warm/hot/too hot" measurements [almost] ANY signal relay is OK.
General purpose relays like those Fujitsus can be replaced with something >>> non-mechanical in MOST (but not all) applications. And there are tons of >>> different ones from different manufacturers if you still need a RELAY -- >>> Fujitsu is not the only player in the field and it is not even unique or any
different from the others.
For something like those low-thermal Cotos there is no replacement. Like it >>> or not but when you enter metrology (or nearby) land you won't have any
other choice. Sure enough it is not a heavily populated land with tons of >>> vegetation at every square inch of it but it still exists and inhabited by >>> very strange creatures.
On Tue, 11 Aug 2026 22:50:16 -0000 (UTC), Sergey Kubushyn
<ksi@koi8.net> wrote:
john larkin <jl@htigct.com> wrote:
On Tue, 11 Aug 2026 20:01:48 -0000 (UTC), Sergey Kubushyn
<ksi@koi8.net> wrote:
john larkin <jl@htigct.com> wrote:
On Tue, 11 Aug 2026 09:15:06 -0400, legg <legg@nospam.magma.ca> wrote: >>>>>
On Mon, 10 Aug 2026 14:46:29 -0700, john larkin <jl@htigct.com> wrote: >>>>>>
https://www.electronicdesign.com/sponsored/video/55394933/quickchat-why-reed-relays-still-matter-in-modern-electronic-design
Does anyone here use reed relays? I recall them being nasty, noisy, >>>>>>> big, expensive, and unreliable.
Doesn't sound like John Larkin.
I thought you'd been using them in fairly large quantities
for a while now - posting about their density and proximity.
Seem to be doing their job on 20 channel multiplexing boards
in my venerable HP34970As for the last 30 years (they count
and record relay operations FYI). These are on replaceable
modules - almost exclusively supplied/refurbished in Malaysia.
I'm carefull around power node sensing - always at least 10R
in series with any sensing wires.
RL
We use no reed relays. Never again!
SSRs are our preferred single-pole switches, but real relays are
closer to ideal switches.
The Fujitsu FTR-B3GA series is wonderful. We've used over 100K so far. >>>>> It's a small, very well-behaved DPDT relay, good to 2 GHz or so, costs >>>>> $1 or so in quantity.
There's a latching version, no thermals.
https://www.dropbox.com/scl/fi/gxdx7d6g1pqy9qgz3jr57/DSC06884.JPG?rlkey=qg3pxra2sh7u4hm995je7kt75&raw=1
https://www.dropbox.com/scl/fi/xopma1w8ialt78fkdd5er/DSC06873.JPG?rlkey=tpmgxvmiq60jcnuj8gnmhwont&raw=1
OK, those will have a HORRIBLE thermal-EMF. Might be OK for switching
something digital or RF but light years from COTO low thermal-EMF relays. >>>> They are from a totally different domain, absolutely non-suitable for low >>>> level signals where a DECENT (not even stellar) precision is needed.
The standard version is only fair, but the latching version has about
zero thermals.
Thermals come from the contacts and the connecting parts. Latching relays
are no different, just different mechanics.
With a latcher there is no continuous coil power dissipation heating everything up. They switch in 2 milliseconds. We have a cute coil
driver circuit that multiplexes nicely.
It takes a thermal gradient, a heat source, to make voltage.
Do they specify thermal EMF for those latching relays? Why would stupid
metrology grade instruments' designers use VERY expensive COTO reed relays >> with whopping <0.5uV thermal EMF instead of those about zero thermal jewels >> that cost $1 a bucketful?
Beats me. I'm just an engineer.
On Tue, 11 Aug 2026 20:30:49 -0000 (UTC), piglet
<erichpwagner@hotmail.com> wrote:
john larkin <jl@htigct.com> wrote:
https://www.electronicdesign.com/sponsored/video/55394933/quickchat-why-reed-relays-still-matter-in-modern-electronic-design
Does anyone here use reed relays? I recall them being nasty, noisy,
big, expensive, and unreliable.
Had great experiences with pricier big name US and European brands and
terrible times with budget Asian brands, contacts sticking was always the
problem despite peak currents limited by resistance to <20mA at worst and
mostly microamps.
Some will stick if left closed for a long time at zero current.
On 12/08/2026 8:50 am, Sergey Kubushyn wrote:
john larkin <jl@htigct.com> wrote:
On Tue, 11 Aug 2026 20:01:48 -0000 (UTC), Sergey Kubushyn
<ksi@koi8.net> wrote:
john larkin <jl@htigct.com> wrote:
On Tue, 11 Aug 2026 09:15:06 -0400, legg <legg@nospam.magma.ca> wrote: >>>>>
On Mon, 10 Aug 2026 14:46:29 -0700, john larkin <jl@htigct.com> wrote: >>>>>>
https://www.electronicdesign.com/sponsored/video/55394933/quickchat-why-reed-relays-still-matter-in-modern-electronic-design
Does anyone here use reed relays? I recall them being nasty, noisy, >>>>>>> big, expensive, and unreliable.
Doesn't sound like John Larkin.
I thought you'd been using them in fairly large quantities
for a while now - posting about their density and proximity.
Seem to be doing their job on 20 channel multiplexing boards
in my venerable HP34970As for the last 30 years (they count
and record relay operations FYI). These are on replaceable
modules - almost exclusively supplied/refurbished in Malaysia.
I'm carefull around power node sensing - always at least 10R
in series with any sensing wires.
RL
We use no reed relays. Never again!
SSRs are our preferred single-pole switches, but real relays are
closer to ideal switches.
The Fujitsu FTR-B3GA series is wonderful. We've used over 100K so far. >>>>> It's a small, very well-behaved DPDT relay, good to 2 GHz or so, costs >>>>> $1 or so in quantity.
There's a latching version, no thermals.
https://www.dropbox.com/scl/fi/gxdx7d6g1pqy9qgz3jr57/DSC06884.JPG?rlkey=qg3pxra2sh7u4hm995je7kt75&raw=1
https://www.dropbox.com/scl/fi/xopma1w8ialt78fkdd5er/DSC06873.JPG?rlkey=tpmgxvmiq60jcnuj8gnmhwont&raw=1
OK, those will have a HORRIBLE thermal-EMF. Might be OK for switching
something digital or RF but light years from COTO low thermal-EMF relays. >>>> They are from a totally different domain, absolutely non-suitable for low >>>> level signals where a DECENT (not even stellar) precision is needed.
The standard version is only fair, but the latching version has about
zero thermals.
Thermals come from the contacts and the connecting parts. Latching relays
are no different, just different mechanics.
Do they specify thermal EMF for those latching relays? Why would stupid
metrology grade instruments' designers use VERY expensive COTO reed relays >> with whopping <0.5uV thermal EMF instead of those about zero thermal jewels >> that cost $1 a bucketful?
Then, they have 1 GOhm insulation resistance which is 3 ORDERS OF MAGNITUDE
worse than low-thermal Cotos. Not TIMES worse but 3 ORDERS OF MAGNITUDE >>>> worse.
In real life they are better. They don't production test $1 relays for
attoamp leakage.
Yeah, they just want to sell them as a cheap junk instead of charging at
least an order of magnitude more... And they don't know that, e.g., $1
Susumu resistors are much better in real life so they buy oil-filled VHP101 >> and such from Vishay for $100+ apiece...
I designed a test mux box using them.
https://www.dropbox.com/scl/fo/6nyerqdbdlno2k98ifjc5/AMmsFfmBte6cb6VW70UHvg8?rlkey=ngzczkb2vv5ho3gfbbqpj2l6i&dl=0
I think that's the biggest PCB that I've ever done.
With a fan in the 3U rackmount box, it multiplexes thermocouples OK. I
should have used the latching relays.
Thermocouples are very crude devices, good to +/- 1 degree Celsius or such >> for the low temperature ones. The high temperature ones are worse. They are >> not anywhere near "precision".
A good Pt probe easily gets to .01 degree precision. A [limited range]
thermistor is even better, .001 degree is achievable.
You do have to calibrate each one to get that. I've used +/-0.2K
Betatherm interchangable thermistors (and Yellow-Springs offer even
tighter spec parts at ten times the price).
Platinum resistance thermometers are much more stable, and 10
microdegrees is attainable (with careful multipoint calibration and linearity correction).
An old Hart/Fluke
Tweener 1504, e.g. has .003 degrees accuracy typical with .0001 degrees
resolution when used with a good probe. An SPRT sibling, 1502, has .006
degrees accuracy with .001 degree resolution. Those are OLD instruments.
Kaye all-in-one (you only provide power and talk over RS-232 with it)
IRTD-400 has a range of -196 to 420 degrees Celsius and has a guaranteed
accuracy of .025 degrees over ENTIRE range with .001 degree resolution. Much >> better farther from extremes.
This is where all those fancy components are used. For a stupid
thermocouples with "cold/warm/hot/too hot" measurements [almost] ANY signal >> relay is OK.
General purpose relays like those Fujitsus can be replaced with something >>>> non-mechanical in MOST (but not all) applications. And there are tons of >>>> different ones from different manufacturers if you still need a RELAY -- >>>> Fujitsu is not the only player in the field and it is not even unique or any
different from the others.
For something like those low-thermal Cotos there is no replacement. Like it
or not but when you enter metrology (or nearby) land you won't have any >>>> other choice. Sure enough it is not a heavily populated land with tons of >>>> vegetation at every square inch of it but it still exists and inhabited by >>>> very strange creatures.
Metrology does get written up in peer-reviewed journals like the Review
of Scientific Instruments. Their refereeing isn't all that reliable and
I've published a few comments there when the refereeing has let them
down badly, but the good stuff can be very good indeed.
Larsen N T 1968 Rev. Sci. Instrum. 39 1rCo12
On 12/08/2026 10:15 am, john larkin wrote:
On Tue, 11 Aug 2026 22:50:16 -0000 (UTC), Sergey Kubushyn
<ksi@koi8.net> wrote:
john larkin <jl@htigct.com> wrote:
On Tue, 11 Aug 2026 20:01:48 -0000 (UTC), Sergey Kubushyn
<ksi@koi8.net> wrote:
john larkin <jl@htigct.com> wrote:
On Tue, 11 Aug 2026 09:15:06 -0400, legg <legg@nospam.magma.ca> wrote: >>>>>>
On Mon, 10 Aug 2026 14:46:29 -0700, john larkin <jl@htigct.com> wrote: >>>>>>>
https://www.electronicdesign.com/sponsored/video/55394933/quickchat-why-reed-relays-still-matter-in-modern-electronic-design
Does anyone here use reed relays? I recall them being nasty, noisy, >>>>>>>> big, expensive, and unreliable.
Doesn't sound like John Larkin.
I thought you'd been using them in fairly large quantities
for a while now - posting about their density and proximity.
Seem to be doing their job on 20 channel multiplexing boards
in my venerable HP34970As for the last 30 years (they count
and record relay operations FYI). These are on replaceable
modules - almost exclusively supplied/refurbished in Malaysia.
I'm carefull around power node sensing - always at least 10R
in series with any sensing wires.
RL
We use no reed relays. Never again!
SSRs are our preferred single-pole switches, but real relays are
closer to ideal switches.
The Fujitsu FTR-B3GA series is wonderful. We've used over 100K so far. >>>>>> It's a small, very well-behaved DPDT relay, good to 2 GHz or so, costs >>>>>> $1 or so in quantity.
There's a latching version, no thermals.
https://www.dropbox.com/scl/fi/gxdx7d6g1pqy9qgz3jr57/DSC06884.JPG?rlkey=qg3pxra2sh7u4hm995je7kt75&raw=1
https://www.dropbox.com/scl/fi/xopma1w8ialt78fkdd5er/DSC06873.JPG?rlkey=tpmgxvmiq60jcnuj8gnmhwont&raw=1
OK, those will have a HORRIBLE thermal-EMF. Might be OK for switching >>>>> something digital or RF but light years from COTO low thermal-EMF relays. >>>>> They are from a totally different domain, absolutely non-suitable for low >>>>> level signals where a DECENT (not even stellar) precision is needed.
The standard version is only fair, but the latching version has about
zero thermals.
Thermals come from the contacts and the connecting parts. Latching relays >>> are no different, just different mechanics.
With a latcher there is no continuous coil power dissipation heating
everything up. They switch in 2 milliseconds. We have a cute coil
driver circuit that multiplexes nicely.
It takes a thermal gradient, a heat source, to make voltage.
Sadly, the relay operating coils aren't the only components that
dissipate power on a printed circuit board. There's always some kind of thermal gradient across a board.
On 12/08/2026 7:59 am, john larkin wrote:
On Tue, 11 Aug 2026 20:30:49 -0000 (UTC), piglet
<erichpwagner@hotmail.com> wrote:
john larkin <jl@htigct.com> wrote:
https://www.electronicdesign.com/sponsored/video/55394933/quickchat-why-reed-relays-still-matter-in-modern-electronic-design
Does anyone here use reed relays? I recall them being nasty, noisy,
big, expensive, and unreliable.
Had great experiences with pricier big name US and European brands and
terrible times with budget Asian brands, contacts sticking was always the >>> problem despite peak currents limited by resistance to <20mA at worst and >>> mostly microamps.
Some will stick if left closed for a long time at zero current.
It's called "vacuum welding". Soft metals - like gold - diffuse into one another if left in contact for long enough.
It happens faster if the temperature is higher. We bonded gold-plated electroformed copper grids to gold-flashed ceramic by squeezing them together for a few minutes at 400C. That's called pressure welding.
Bill Sloman <bill.sloman@ieee.org> wrote:
On 12/08/2026 10:15 am, john larkin wrote:
On Tue, 11 Aug 2026 22:50:16 -0000 (UTC), Sergey Kubushyn
<ksi@koi8.net> wrote:
john larkin <jl@htigct.com> wrote:
On Tue, 11 Aug 2026 20:01:48 -0000 (UTC), Sergey Kubushyn
<ksi@koi8.net> wrote:
john larkin <jl@htigct.com> wrote:The standard version is only fair, but the latching version has about >>>>> zero thermals.
On Tue, 11 Aug 2026 09:15:06 -0400, legg <legg@nospam.magma.ca> wrote: >>>>>>>
On Mon, 10 Aug 2026 14:46:29 -0700, john larkin <jl@htigct.com> wrote: >>>>>>>>
https://www.electronicdesign.com/sponsored/video/55394933/quickchat-why-reed-relays-still-matter-in-modern-electronic-design
Does anyone here use reed relays? I recall them being nasty, noisy, >>>>>>>>> big, expensive, and unreliable.
Doesn't sound like John Larkin.
I thought you'd been using them in fairly large quantities
for a while now - posting about their density and proximity.
Seem to be doing their job on 20 channel multiplexing boards
in my venerable HP34970As for the last 30 years (they count
and record relay operations FYI). These are on replaceable
modules - almost exclusively supplied/refurbished in Malaysia. >>>>>>>>
I'm carefull around power node sensing - always at least 10R
in series with any sensing wires.
RL
We use no reed relays. Never again!
SSRs are our preferred single-pole switches, but real relays are >>>>>>> closer to ideal switches.
The Fujitsu FTR-B3GA series is wonderful. We've used over 100K so far. >>>>>>> It's a small, very well-behaved DPDT relay, good to 2 GHz or so, costs >>>>>>> $1 or so in quantity.
There's a latching version, no thermals.
https://www.dropbox.com/scl/fi/gxdx7d6g1pqy9qgz3jr57/DSC06884.JPG?rlkey=qg3pxra2sh7u4hm995je7kt75&raw=1
https://www.dropbox.com/scl/fi/xopma1w8ialt78fkdd5er/DSC06873.JPG?rlkey=tpmgxvmiq60jcnuj8gnmhwont&raw=1
OK, those will have a HORRIBLE thermal-EMF. Might be OK for switching >>>>>> something digital or RF but light years from COTO low thermal-EMF relays.
They are from a totally different domain, absolutely non-suitable for low
level signals where a DECENT (not even stellar) precision is needed. >>>>>
Thermals come from the contacts and the connecting parts. Latching relays >>>> are no different, just different mechanics.
With a latcher there is no continuous coil power dissipation heating
everything up. They switch in 2 milliseconds. We have a cute coil
driver circuit that multiplexes nicely.
It takes a thermal gradient, a heat source, to make voltage.
Sadly, the relay operating coils aren't the only components that
dissipate power on a printed circuit board. There's always some kind of
thermal gradient across a board.
Exactly. A sensitive instrument even senses your breathing from several feet >with its pure copper terminals shorted with pure copper.
single ppm you have to keep your entire setup within closed thermally >insulated box. Or at least keep tens of feet distance from it and control it >remotely. A slightest draft can set you off by tens ppm. That is copper--- Synchronet 3.22a-Linux NewsLink 1.2
on copper, CRIMPED pure copper wires.
Very noticeable with, e.g. HP419A null voltmeter on the most sensitive 3uV >full-scale range with a shorted input. It is ANALOG so it is fascinating to >see how the needle moves following your breathing at something like 5 feet >from it. When AC starts in the room it pegs the needle :)
---
******************************************************************
* KSI@home KOI8 Net < > The impossible we do immediately. *
* Las Vegas NV, USA < > Miracles require 24-hour notice. * >******************************************************************
On Wed, 12 Aug 2026 06:16:03 -0000 (UTC), Sergey Kubushyn
<ksi@koi8.net> wrote:
Bill Sloman <bill.sloman@ieee.org> wrote:
On 12/08/2026 10:15 am, john larkin wrote:
On Tue, 11 Aug 2026 22:50:16 -0000 (UTC), Sergey Kubushyn
<ksi@koi8.net> wrote:
john larkin <jl@htigct.com> wrote:
On Tue, 11 Aug 2026 20:01:48 -0000 (UTC), Sergey Kubushyn
<ksi@koi8.net> wrote:
john larkin <jl@htigct.com> wrote:The standard version is only fair, but the latching version has about >>>>>> zero thermals.
On Tue, 11 Aug 2026 09:15:06 -0400, legg <legg@nospam.magma.ca> wrote: >>>>>>>>
On Mon, 10 Aug 2026 14:46:29 -0700, john larkin <jl@htigct.com> wrote:
https://www.electronicdesign.com/sponsored/video/55394933/quickchat-why-reed-relays-still-matter-in-modern-electronic-design
Does anyone here use reed relays? I recall them being nasty, noisy, >>>>>>>>>> big, expensive, and unreliable.
Doesn't sound like John Larkin.
I thought you'd been using them in fairly large quantities
for a while now - posting about their density and proximity. >>>>>>>>>
Seem to be doing their job on 20 channel multiplexing boards >>>>>>>>> in my venerable HP34970As for the last 30 years (they count
and record relay operations FYI). These are on replaceable
modules - almost exclusively supplied/refurbished in Malaysia. >>>>>>>>>
I'm carefull around power node sensing - always at least 10R >>>>>>>>> in series with any sensing wires.
RL
We use no reed relays. Never again!
SSRs are our preferred single-pole switches, but real relays are >>>>>>>> closer to ideal switches.
The Fujitsu FTR-B3GA series is wonderful. We've used over 100K so far. >>>>>>>> It's a small, very well-behaved DPDT relay, good to 2 GHz or so, costs >>>>>>>> $1 or so in quantity.
There's a latching version, no thermals.
https://www.dropbox.com/scl/fi/gxdx7d6g1pqy9qgz3jr57/DSC06884.JPG?rlkey=qg3pxra2sh7u4hm995je7kt75&raw=1
https://www.dropbox.com/scl/fi/xopma1w8ialt78fkdd5er/DSC06873.JPG?rlkey=tpmgxvmiq60jcnuj8gnmhwont&raw=1
OK, those will have a HORRIBLE thermal-EMF. Might be OK for switching >>>>>>> something digital or RF but light years from COTO low thermal-EMF relays.
They are from a totally different domain, absolutely non-suitable for low
level signals where a DECENT (not even stellar) precision is needed. >>>>>>
Thermals come from the contacts and the connecting parts. Latching relays >>>>> are no different, just different mechanics.
With a latcher there is no continuous coil power dissipation heating
everything up. They switch in 2 milliseconds. We have a cute coil
driver circuit that multiplexes nicely.
It takes a thermal gradient, a heat source, to make voltage.
Sadly, the relay operating coils aren't the only components that
dissipate power on a printed circuit board. There's always some kind of
thermal gradient across a board.
Exactly. A sensitive instrument even senses your breathing from several feet >> with its pure copper terminals shorted with pure copper.
That's crazy.
Bill Sloman wrote:
On 12/08/2026 7:59 am, john larkin wrote:
On Tue, 11 Aug 2026 20:30:49 -0000 (UTC), piglet
<erichpwagner@hotmail.com> wrote:
john larkin <jl@htigct.com> wrote:
https://www.electronicdesign.com/sponsored/video/55394933/quickchat-why-reed-relays-still-matter-in-modern-electronic-design
Does anyone here use reed relays? I recall them being nasty, noisy,
big, expensive, and unreliable.
Had great experiences with pricier big name US and European brands and >>>> terrible times with budget Asian brands, contacts sticking was
always the
problem despite peak currents limited by resistance to <20mA at
worst and
mostly microamps.
Some will stick if left closed for a long time at zero current.
It's called "vacuum welding". Soft metals - like gold - diffuse into
one another if left in contact for long enough.
It happens faster if the temperature is higher. We bonded gold-plated
electroformed copper grids to gold-flashed ceramic by squeezing them
together for a few minutes at 400C. That's called pressure welding.
We did the same to bond gold beam leaded silicon devices to large
ceramics with gold paths back in the 70's and 80's. These large hybrids
are still used in telecommunication central office and #4 Toll switching centers. Here the process was called thermocompression bonding. It took
less than a second using a heated tool and pressure.
On 12/08/2026 4:04 pm, Sergey Kubushyn wrote:
Bill Sloman <bill.sloman@ieee.org> wrote:
On 12/08/2026 8:50 am, Sergey Kubushyn wrote:
john larkin <jl@htigct.com> wrote:
On Tue, 11 Aug 2026 20:01:48 -0000 (UTC), Sergey Kubushyn
<ksi@koi8.net> wrote:
john larkin <jl@htigct.com> wrote:The standard version is only fair, but the latching version has about >>>>> zero thermals.
On Tue, 11 Aug 2026 09:15:06 -0400, legg <legg@nospam.magma.ca> >>>>>>> wrote:
On Mon, 10 Aug 2026 14:46:29 -0700, john larkin <jl@htigct.com> >>>>>>>> wrote:
https://www.electronicdesign.com/sponsored/video/55394933/quickchat-why-reed-relays-still-matter-in-modern-electronic-design
Does anyone here use reed relays? I recall them being nasty, >>>>>>>>> noisy,
big, expensive, and unreliable.
Doesn't sound like John Larkin.
I thought you'd been using them in fairly large quantities
for a while now - posting about their density and proximity.
Seem to be doing their job on 20 channel multiplexing boards
in my venerable HP34970As for the last 30 years (they count
and record relay operations FYI). These are on replaceable
modules - almost exclusively supplied/refurbished in Malaysia. >>>>>>>>
I'm carefull around power node sensing - always at least 10R
in series with any sensing wires.
RL
We use no reed relays. Never again!
SSRs are our preferred single-pole switches, but real relays are >>>>>>> closer to ideal switches.
The Fujitsu FTR-B3GA series is wonderful. We've used over 100K so >>>>>>> far.
It's a small, very well-behaved DPDT relay, good to 2 GHz or so, >>>>>>> costs
$1 or so in quantity.
There's a latching version, no thermals.
https://www.dropbox.com/scl/fi/gxdx7d6g1pqy9qgz3jr57/DSC06884.JPG?rlkey=qg3pxra2sh7u4hm995je7kt75&raw=1
https://www.dropbox.com/scl/fi/xopma1w8ialt78fkdd5er/DSC06873.JPG?rlkey=tpmgxvmiq60jcnuj8gnmhwont&raw=1
OK, those will have a HORRIBLE thermal-EMF. Might be OK for switching >>>>>> something digital or RF but light years from COTO low thermal-EMF >>>>>> relays.
They are from a totally different domain, absolutely non-suitable >>>>>> for low
level signals where a DECENT (not even stellar) precision is needed. >>>>>
Thermals come from the contacts and the connecting parts. Latching
relays
are no different, just different mechanics.
Do they specify thermal EMF for those latching relays? Why would stupid >>>> metrology grade instruments' designers use VERY expensive COTO reed
relays
with whopping <0.5uV thermal EMF instead of those about zero thermal
jewels
that cost $1 a bucketful?
Then, they have 1 GOhm insulation resistance which is 3 ORDERS OF >>>>>> MAGNITUDE
worse than low-thermal Cotos. Not TIMES worse but 3 ORDERS OF
MAGNITUDE
worse.
In real life they are better. They don't production test $1 relays for >>>>> attoamp leakage.
Yeah, they just want to sell them as a cheap junk instead of
charging at
least an order of magnitude more... And they don't know that, e.g., $1 >>>> Susumu resistors are much better in real life so they buy oil-filled
VHP101
and such from Vishay for $100+ apiece...
I designed a test mux box using them.
https://www.dropbox.com/scl/fo/6nyerqdbdlno2k98ifjc5/AMmsFfmBte6cb6VW70UHvg8?rlkey=ngzczkb2vv5ho3gfbbqpj2l6i&dl=0
I think that's the biggest PCB that I've ever done.
With a fan in the 3U rackmount box, it multiplexes thermocouples OK. I >>>>> should have used the latching relays.
Thermocouples are very crude devices, good to +/- 1 degree Celsius
or such
for the low temperature ones. The high temperature ones are worse.
They are
not anywhere near "precision".
A good Pt probe easily gets to .01 degree precision. A [limited range] >>>> thermistor is even better, .001 degree is achievable.
You do have to calibrate each one to get that. I've used +/-0.2K
Betatherm interchangable thermistors (and Yellow-Springs offer even
tighter spec parts at ten times the price).
Sure. However, there are better thermistor PROBES, with very precise
calibration and VERY stable. They are NOT interchangeable and have
limited
measurement range but they are very precise within that range.
I have Amphenol calibrated Fluke 5640-D probe with calibration
certificate
thicker than an average manual. It has .0015 degrees Celsius accuracy
from 0
to 60 degrees and .005 degrees per year drift. Paired with Hart/Fluke
Tweener 1504 it is accurate to that .0015 degrees.
Good Thermistor Standard probes are extremely accurate and very
stable, with
very low drift. Calibrated Tweener 1504 matches that accuracy and very
easy
to calibrate with a set of calibration resistors made of Vishay VHP101
resistors. It is probably the ultimate precision combination for a
limited
temperature range. Can be checked with a TPW and Gallium cells at 2
points
within their range.
PRT does not allow for such precision because its thermal coefficient is
musch lower so it is difficult to measure to the precision that
thermistor
standard gives.
Platinium resistance thermoneters are made from very pure platinum, and
just platinum, and have a positive temperature coefficient. Thermistors
are sintered metal oxides and the useful ones have negative temperature coefficients. That introduces problems.
Platinum resistance thermometers are much more stable, and 10
microdegrees is attainable (with careful multipoint calibration and
linearity correction).
You'll need a VERY precise/stable current source and very high resolution
and low noise ADC to get that precision from a PRT -- the resistance
change
for 10 microdegrees can be easily less than your noise floor... Much
easier
with a thermistor with its crazy sensitivity but lower temperature
range...
You don't use an ADC. You use an AC bridge built with ratio transformers
"Coaxial AC Bridges" By B P Kipple and G H Rayner, ISBN 0-85274-389-0
is a useful text on the subject. 10:1 ratio transformers (with eleven taps)-a are accurate to about 0.1 parts per million, so it is worth
stacking up six of them. 2:1 (bifilar wound) parts are accurate to about
1 part per billion so you could stack up more, but you'd only use them
for the top end.
The winding techniques get complicated. Rope windings are easy, but you
can do better. Strap windings offer a lot advantages but are hard to realise. Ribbon cable could offer some interesting options - not a lot
of copper per unit volume, but it is easy to buy in long lengths.
What was the failure? Open contacts?
Seems the main problem is the excessive research required to select the
most appropriate relay for the application, and to verify the attributes
of the received batch before use. You can hold back a representative
sample for long-term testing in anticipation of a future recall.
On 13/08/2026 4:45 am, someone wrote:
What was the failure? Open contacts?
Seems the main problem is the excessive research required to select the
most appropriate relay for the application, and to verify the attributes
of the received batch before use. You can hold back a representative
sample for long-term testing in anticipation of a future recall.
Presumably you are reacting to John Larkin's original post.
He won't know why he thinks his reed relays failed. He probably managed
to try to make them break contact while in series with an inductor,
which can weld the contacts together.
The usual failure mode is that the contact resistance gets too high.
Each make and break roughens up the contact area and eventually the >conducting area present when the contacts are closed is too small.
They typically offer 10 million operations
Mercury wetted relays don't have that problem, and last about ten times >longer than dry-reed relays, but their contact resistance also rises
with repeated cycling.
There are shielded versions available, mainly to achieve high density interference free mounting, but the benefit extends to any nearby hazard or victim component.
https://cototechnology.com/library/datasheet/cotoclassic-9091-9092-series-reed-relay-datasheet.pdf
Note the 0.5msec total operating time that includes bounce.
It would be rare for the manufacturer to use different metals across mating contacts, especially for relays intended for instrumentation applications. The two metals actually used are to make a single contact. That would be something like an iron alloy for the reed itself and then a low-contact-resistance material like Rhodium plated at the contact point. Since the two contacts are identical, the thermocouple voltages cancel. But things can happen the disrupt that symmetry and EMF cancellation: (from AI)
Fritting and Micro-Arcing (Electrical Stress): If you switch a signal that has slightly too much voltage or current, a tiny electrical spark or a microscopic "fritting" event occurs right as the blades touch. This creates a localized burst of heat on just one side of the contact face. This microscopic temperature imbalance breaks the symmetry, generating a brief thermal voltage spike across the contacts.
Peltier Heating (DC Current Bias): If you continuously pass a relatively high DC current through the closed contacts, the Peltier effect will naturally pump heat from one blade tip to the other. This creates a permanent temperature difference between the two halves of the contact interface, forcing the contact point to act as an active thermocouple.
And those application-specific problems can appear regardless of the manufacturer's advertised low contact EMF.
EMF problems that people are mostly seeing are the thermocouples at the junctions of component leads/posts and the copper traces on the PCBs. This is again symmetrical, but proximal and asymmetrical heat sources, even the relay coil heat itself, can disrupt the cancellation.
It's hard to believe you can have low signal failures with the reeds advertised for instrumentation applications. There are all kinds of things that destroy the performance, and it's mostly bad manufacturing or mishandling: (from AI)
Micro-Cracks in the Glass Seal: If the glass-to-metal seal gets a microscopic crack during manufacturing, shipping, or soldering, the inert gas will leak out and oxygen will leak in. Once air is inside, the blades will begin to oxidize, causing the classic low-voltage connection failure.
Organic Outgassing Contamination: If the manufacturing facility is not 100% sterile, trace amounts of organic compounds or cleaning solvents can get trapped inside the glass capsule before it is sealed. Over millions of cycles, the physical impact of the blades can cause these trapped organic molecules to break down into a thin polymer film right on the contact point, blocking low-voltage signals.
Plating Flaws: If the sputtered rhodium or ruthenium plating peels or blisters off the underlying nickel-iron blade, the raw base metal is exposed. This can cause erratic contact resistance.
Mechanical Shock Damage: Dropping a reed relay can slightly bend or misalign the internal blades. If the magnetic field from the coil can no longer pull them together with enough physical force to flatten out the microscopic contact points, contact resistance will spike.
On 13/08/2026 1:47 am, john larkin wrote:
On Wed, 12 Aug 2026 06:16:03 -0000 (UTC), Sergey Kubushyn
<ksi@koi8.net> wrote:
Bill Sloman <bill.sloman@ieee.org> wrote:
On 12/08/2026 10:15 am, john larkin wrote:
On Tue, 11 Aug 2026 22:50:16 -0000 (UTC), Sergey Kubushyn
<ksi@koi8.net> wrote:
john larkin <jl@htigct.com> wrote:
On Tue, 11 Aug 2026 20:01:48 -0000 (UTC), Sergey Kubushyn
<ksi@koi8.net> wrote:
john larkin <jl@htigct.com> wrote:The standard version is only fair, but the latching version has about >>>>>>> zero thermals.
On Tue, 11 Aug 2026 09:15:06 -0400, legg <legg@nospam.magma.ca> wrote:
On Mon, 10 Aug 2026 14:46:29 -0700, john larkin <jl@htigct.com> wrote:
https://www.electronicdesign.com/sponsored/video/55394933/quickchat-why-reed-relays-still-matter-in-modern-electronic-design
Does anyone here use reed relays? I recall them being nasty, noisy, >>>>>>>>>>> big, expensive, and unreliable.
Doesn't sound like John Larkin.
I thought you'd been using them in fairly large quantities >>>>>>>>>> for a while now - posting about their density and proximity. >>>>>>>>>>
Seem to be doing their job on 20 channel multiplexing boards >>>>>>>>>> in my venerable HP34970As for the last 30 years (they count >>>>>>>>>> and record relay operations FYI). These are on replaceable >>>>>>>>>> modules - almost exclusively supplied/refurbished in Malaysia. >>>>>>>>>>
I'm carefull around power node sensing - always at least 10R >>>>>>>>>> in series with any sensing wires.
RL
We use no reed relays. Never again!
SSRs are our preferred single-pole switches, but real relays are >>>>>>>>> closer to ideal switches.
The Fujitsu FTR-B3GA series is wonderful. We've used over 100K so far.
It's a small, very well-behaved DPDT relay, good to 2 GHz or so, costs
$1 or so in quantity.
There's a latching version, no thermals.
https://www.dropbox.com/scl/fi/gxdx7d6g1pqy9qgz3jr57/DSC06884.JPG?rlkey=qg3pxra2sh7u4hm995je7kt75&raw=1
https://www.dropbox.com/scl/fi/xopma1w8ialt78fkdd5er/DSC06873.JPG?rlkey=tpmgxvmiq60jcnuj8gnmhwont&raw=1
OK, those will have a HORRIBLE thermal-EMF. Might be OK for switching >>>>>>>> something digital or RF but light years from COTO low thermal-EMF relays.
They are from a totally different domain, absolutely non-suitable for low
level signals where a DECENT (not even stellar) precision is needed. >>>>>>>
Thermals come from the contacts and the connecting parts. Latching relays
are no different, just different mechanics.
With a latcher there is no continuous coil power dissipation heating >>>>> everything up. They switch in 2 milliseconds. We have a cute coil
driver circuit that multiplexes nicely.
It takes a thermal gradient, a heat source, to make voltage.
Sadly, the relay operating coils aren't the only components that
dissipate power on a printed circuit board. There's always some kind of >>>> thermal gradient across a board.
Exactly. A sensitive instrument even senses your breathing from several feet
with its pure copper terminals shorted with pure copper.
That's crazy.
There's nothing crazy about it. The micro-climate inside a closed room >reacts to small temperate difference (and your exhaled breath is warmer
than room temperature) by creating convection currents which act to
reduce the temperature differences. I once had to put draft shields >(cylinders of paper) around a sensitive weighing head when I was testing
it in the lab.
<snip>
On Thu, 13 Aug 2026 17:26:39 +1000, Bill Sloman <bill.sloman@ieee.org>
wrote:
On 13/08/2026 1:47 am, john larkin wrote:
On Wed, 12 Aug 2026 06:16:03 -0000 (UTC), Sergey Kubushyn
<ksi@koi8.net> wrote:
Bill Sloman <bill.sloman@ieee.org> wrote:
On 12/08/2026 10:15 am, john larkin wrote:
On Tue, 11 Aug 2026 22:50:16 -0000 (UTC), Sergey Kubushyn
<ksi@koi8.net> wrote:
john larkin <jl@htigct.com> wrote:
On Tue, 11 Aug 2026 20:01:48 -0000 (UTC), Sergey Kubushyn
<ksi@koi8.net> wrote:
john larkin <jl@htigct.com> wrote:The standard version is only fair, but the latching version has about >>>>>>>> zero thermals.
On Tue, 11 Aug 2026 09:15:06 -0400, legg <legg@nospam.magma.ca> wrote:
On Mon, 10 Aug 2026 14:46:29 -0700, john larkin <jl@htigct.com> wrote:
https://www.electronicdesign.com/sponsored/video/55394933/quickchat-why-reed-relays-still-matter-in-modern-electronic-design
Does anyone here use reed relays? I recall them being nasty, noisy,
big, expensive, and unreliable.
Doesn't sound like John Larkin.
I thought you'd been using them in fairly large quantities >>>>>>>>>>> for a while now - posting about their density and proximity. >>>>>>>>>>>
Seem to be doing their job on 20 channel multiplexing boards >>>>>>>>>>> in my venerable HP34970As for the last 30 years (they count >>>>>>>>>>> and record relay operations FYI). These are on replaceable >>>>>>>>>>> modules - almost exclusively supplied/refurbished in Malaysia. >>>>>>>>>>>
I'm carefull around power node sensing - always at least 10R >>>>>>>>>>> in series with any sensing wires.
RL
We use no reed relays. Never again!
SSRs are our preferred single-pole switches, but real relays are >>>>>>>>>> closer to ideal switches.
The Fujitsu FTR-B3GA series is wonderful. We've used over 100K so far.
It's a small, very well-behaved DPDT relay, good to 2 GHz or so, costs
$1 or so in quantity.
There's a latching version, no thermals.
https://www.dropbox.com/scl/fi/gxdx7d6g1pqy9qgz3jr57/DSC06884.JPG?rlkey=qg3pxra2sh7u4hm995je7kt75&raw=1
https://www.dropbox.com/scl/fi/xopma1w8ialt78fkdd5er/DSC06873.JPG?rlkey=tpmgxvmiq60jcnuj8gnmhwont&raw=1
OK, those will have a HORRIBLE thermal-EMF. Might be OK for switching >>>>>>>>> something digital or RF but light years from COTO low thermal-EMF relays.
They are from a totally different domain, absolutely non-suitable for low
level signals where a DECENT (not even stellar) precision is needed. >>>>>>>>
Thermals come from the contacts and the connecting parts. Latching relays
are no different, just different mechanics.
With a latcher there is no continuous coil power dissipation heating >>>>>> everything up. They switch in 2 milliseconds. We have a cute coil
driver circuit that multiplexes nicely.
It takes a thermal gradient, a heat source, to make voltage.
Sadly, the relay operating coils aren't the only components that
dissipate power on a printed circuit board. There's always some kind of >>>>> thermal gradient across a board.
Exactly. A sensitive instrument even senses your breathing from several feet
with its pure copper terminals shorted with pure copper.
That's crazy.
There's nothing crazy about it. The micro-climate inside a closed room >>reacts to small temperate difference (and your exhaled breath is warmer >>than room temperature) by creating convection currents which act to
reduce the temperature differences. I once had to put draft shields >>(cylinders of paper) around a sensitive weighing head when I was testing
it in the lab.
<snip>
Do the math.
What's the Seebeck coefficient of a copper-copper junction?
On Wed, 12 Aug 2026 18:45:02 +0000, someone <2a59d59e3809f827ce709d3815e3950eef4a6a93af5557a93a7fdfba71460843@example.com>
wrote:
There are shielded versions available, mainly to achieve high density interference free mounting, but the benefit extends to any nearby hazard or victim component.
https://cototechnology.com/library/datasheet/cotoclassic-9091-9092-series-reed-relay-datasheet.pdf
Note the 0.5msec total operating time that includes bounce.
It would be rare for the manufacturer to use different metals across mating contacts, especially for relays intended for instrumentation applications. The two metals actually used are to make a single contact. That would be something like an iron alloy for the reed itself and then a low-contact-resistance material like Rhodium plated at the contact point. Since the two contacts are identical, the thermocouple voltages cancel. But things can happen the disrupt that symmetry and EMF cancellation: (from AI)
Fritting and Micro-Arcing (Electrical Stress): If you switch a signal that has slightly too much voltage or current, a tiny electrical spark or a microscopic "fritting" event occurs right as the blades touch. This creates a localized burst of heat on just one side of the contact face. This microscopic temperature imbalance breaks the symmetry, generating a brief thermal voltage spike across the contacts.
Peltier Heating (DC Current Bias): If you continuously pass a relatively high DC current through the closed contacts, the Peltier effect will naturally pump heat from one blade tip to the other. This creates a permanent temperature difference between the two halves of the contact interface, forcing the contact point to act as an active thermocouple.
And those application-specific problems can appear regardless of the manufacturer's advertised low contact EMF.
EMF problems that people are mostly seeing are the thermocouples at the junctions of component leads/posts and the copper traces on the PCBs. This is again symmetrical, but proximal and asymmetrical heat sources, even the relay coil heat itself, can disrupt the cancellation.
It's hard to believe you can have low signal failures with the reeds advertised for instrumentation applications. There are all kinds of things that destroy the performance, and it's mostly bad manufacturing or mishandling: (from AI)
Micro-Cracks in the Glass Seal: If the glass-to-metal seal gets a microscopic crack during manufacturing, shipping, or soldering, the inert gas will leak out and oxygen will leak in. Once air is inside, the blades will begin to oxidize, causing the classic low-voltage connection failure.
Organic Outgassing Contamination: If the manufacturing facility is not 100% sterile, trace amounts of organic compounds or cleaning solvents can get trapped inside the glass capsule before it is sealed. Over millions of cycles, the physical impact of the blades can cause these trapped organic molecules to break down into a thin polymer film right on the contact point, blocking low-voltage signals.
Right. Real relays can have redundant contacts with some wiping
actions. A micro-inch of contamination can insulate reeds.
Plating Flaws: If the sputtered rhodium or ruthenium plating peels or blisters off the underlying nickel-iron blade, the raw base metal is exposed. This can cause erratic contact resistance.
Mechanical Shock Damage: Dropping a reed relay can slightly bend or misalign the internal blades. If the magnetic field from the coil can no longer pull them together with enough physical force to flatten out the microscopic contact points, contact resistance will spike.
The Coto part is about $4.50 for SPST.
Some reeds switch fast, but twang for milliseconds.
john larkin <jl@htigct.com> wrote:
On Thu, 13 Aug 2026 17:26:39 +1000, Bill Sloman <bill.sloman@ieee.org>
wrote:
On 13/08/2026 1:47 am, john larkin wrote:
On Wed, 12 Aug 2026 06:16:03 -0000 (UTC), Sergey Kubushyn
<ksi@koi8.net> wrote:
Bill Sloman <bill.sloman@ieee.org> wrote:
On 12/08/2026 10:15 am, john larkin wrote:
On Tue, 11 Aug 2026 22:50:16 -0000 (UTC), Sergey Kubushyn
<ksi@koi8.net> wrote:
john larkin <jl@htigct.com> wrote:
On Tue, 11 Aug 2026 20:01:48 -0000 (UTC), Sergey Kubushyn
<ksi@koi8.net> wrote:
john larkin <jl@htigct.com> wrote:The standard version is only fair, but the latching version has about >>>>>>>>> zero thermals.
On Tue, 11 Aug 2026 09:15:06 -0400, legg <legg@nospam.magma.ca> wrote:
On Mon, 10 Aug 2026 14:46:29 -0700, john larkin <jl@htigct.com> wrote:
https://www.electronicdesign.com/sponsored/video/55394933/quickchat-why-reed-relays-still-matter-in-modern-electronic-design
Does anyone here use reed relays? I recall them being nasty, noisy,
big, expensive, and unreliable.
Doesn't sound like John Larkin.
I thought you'd been using them in fairly large quantities >>>>>>>>>>>> for a while now - posting about their density and proximity. >>>>>>>>>>>>
Seem to be doing their job on 20 channel multiplexing boards >>>>>>>>>>>> in my venerable HP34970As for the last 30 years (they count >>>>>>>>>>>> and record relay operations FYI). These are on replaceable >>>>>>>>>>>> modules - almost exclusively supplied/refurbished in Malaysia. >>>>>>>>>>>>
I'm carefull around power node sensing - always at least 10R >>>>>>>>>>>> in series with any sensing wires.
RL
We use no reed relays. Never again!
SSRs are our preferred single-pole switches, but real relays are >>>>>>>>>>> closer to ideal switches.
The Fujitsu FTR-B3GA series is wonderful. We've used over 100K so far.
It's a small, very well-behaved DPDT relay, good to 2 GHz or so, costs
$1 or so in quantity.
There's a latching version, no thermals.
https://www.dropbox.com/scl/fi/gxdx7d6g1pqy9qgz3jr57/DSC06884.JPG?rlkey=qg3pxra2sh7u4hm995je7kt75&raw=1
https://www.dropbox.com/scl/fi/xopma1w8ialt78fkdd5er/DSC06873.JPG?rlkey=tpmgxvmiq60jcnuj8gnmhwont&raw=1
OK, those will have a HORRIBLE thermal-EMF. Might be OK for switching
something digital or RF but light years from COTO low thermal-EMF relays.
They are from a totally different domain, absolutely non-suitable for low
level signals where a DECENT (not even stellar) precision is needed. >>>>>>>>>
Thermals come from the contacts and the connecting parts. Latching relays
are no different, just different mechanics.
With a latcher there is no continuous coil power dissipation heating >>>>>>> everything up. They switch in 2 milliseconds. We have a cute coil >>>>>>> driver circuit that multiplexes nicely.
It takes a thermal gradient, a heat source, to make voltage.
Sadly, the relay operating coils aren't the only components that
dissipate power on a printed circuit board. There's always some kind of >>>>>> thermal gradient across a board.
Exactly. A sensitive instrument even senses your breathing from several feet
with its pure copper terminals shorted with pure copper.
That's crazy.
There's nothing crazy about it. The micro-climate inside a closed room
reacts to small temperate difference (and your exhaled breath is warmer >>> than room temperature) by creating convection currents which act to
reduce the temperature differences. I once had to put draft shields
(cylinders of paper) around a sensitive weighing head when I was testing >>> it in the lab.
<snip>
Do the math.
What's the Seebeck coefficient of a copper-copper junction?
Unfortunately it is not the MATH that deflects the meter's needle. Nobody's perfect, you know... Your copper is not 100% copper, not monocrystalline, there are oxides/sulfides and other impurities on both contacting surfaces and there is something BEHIND those binding posts somehow connected to them...
When you measure resistance (or whatever) with even venerable 3458A that
took all known measures to compensate for all ill effects, you don't just hook the DUT to it and read what it shows. That is if you want accuracy better than that from a $20 multimeter from Amazon or eBay. You choose a range MANUALLY, use a manual trigger after letting everything to get into thermal equilibrium for at least several minutes, throw away the first measurement and take the second. You almost always need to cover the input terminals and DUT terminals or somehow thermally insulate them. The probes' wiring is also critical -- there is leakage that can steal precious ppms by shunting your DUT, triboelectric effects, EMI noise and much more.
Sure enough you don't have to bother with all that crazy trickery if 0.1% accuracy is more than sufficient for you. The math will work just fine.
Just try it yourself. Connect, say, a decent standard resistor to 3458A, put it to auto-trigger and let it run for, say, half-hour observing it from far away or remotely over GPIB. Then come closer, say within 5 feet, and see the last 2-3 digits change.
---
******************************************************************
* KSI@home KOI8 Net < > The impossible we do immediately. *
* Las Vegas NV, USA < > Miracles require 24-hour notice. * ******************************************************************
On Thu, 13 Aug 2026 17:26:39 +1000, Bill Sloman <bill.sloman@ieee.org>
wrote:
On 13/08/2026 1:47 am, john larkin wrote:
On Wed, 12 Aug 2026 06:16:03 -0000 (UTC), Sergey Kubushyn
<ksi@koi8.net> wrote:
Bill Sloman <bill.sloman@ieee.org> wrote:
On 12/08/2026 10:15 am, john larkin wrote:
On Tue, 11 Aug 2026 22:50:16 -0000 (UTC), Sergey Kubushyn
<ksi@koi8.net> wrote:
john larkin <jl@htigct.com> wrote:
On Tue, 11 Aug 2026 20:01:48 -0000 (UTC), Sergey Kubushyn
<ksi@koi8.net> wrote:
john larkin <jl@htigct.com> wrote:The standard version is only fair, but the latching version has about >>>>>>>> zero thermals.
On Tue, 11 Aug 2026 09:15:06 -0400, legg <legg@nospam.magma.ca> wrote:
On Mon, 10 Aug 2026 14:46:29 -0700, john larkin <jl@htigct.com> wrote:
https://www.electronicdesign.com/sponsored/video/55394933/quickchat-why-reed-relays-still-matter-in-modern-electronic-design
Does anyone here use reed relays? I recall them being nasty, noisy,
big, expensive, and unreliable.
Doesn't sound like John Larkin.
I thought you'd been using them in fairly large quantities >>>>>>>>>>> for a while now - posting about their density and proximity. >>>>>>>>>>>
Seem to be doing their job on 20 channel multiplexing boards >>>>>>>>>>> in my venerable HP34970As for the last 30 years (they count >>>>>>>>>>> and record relay operations FYI). These are on replaceable >>>>>>>>>>> modules - almost exclusively supplied/refurbished in Malaysia. >>>>>>>>>>>
I'm carefull around power node sensing - always at least 10R >>>>>>>>>>> in series with any sensing wires.
RL
We use no reed relays. Never again!
SSRs are our preferred single-pole switches, but real relays are >>>>>>>>>> closer to ideal switches.
The Fujitsu FTR-B3GA series is wonderful. We've used over 100K so far.
It's a small, very well-behaved DPDT relay, good to 2 GHz or so, costs
$1 or so in quantity.
There's a latching version, no thermals.
https://www.dropbox.com/scl/fi/gxdx7d6g1pqy9qgz3jr57/DSC06884.JPG?rlkey=qg3pxra2sh7u4hm995je7kt75&raw=1
https://www.dropbox.com/scl/fi/xopma1w8ialt78fkdd5er/DSC06873.JPG?rlkey=tpmgxvmiq60jcnuj8gnmhwont&raw=1
OK, those will have a HORRIBLE thermal-EMF. Might be OK for switching >>>>>>>>> something digital or RF but light years from COTO low thermal-EMF relays.
They are from a totally different domain, absolutely non-suitable for low
level signals where a DECENT (not even stellar) precision is needed. >>>>>>>>
Thermals come from the contacts and the connecting parts. Latching relays
are no different, just different mechanics.
With a latcher there is no continuous coil power dissipation heating >>>>>> everything up. They switch in 2 milliseconds. We have a cute coil
driver circuit that multiplexes nicely.
It takes a thermal gradient, a heat source, to make voltage.
Sadly, the relay operating coils aren't the only components that
dissipate power on a printed circuit board. There's always some kind of >>>>> thermal gradient across a board.
Exactly. A sensitive instrument even senses your breathing from several feet
with its pure copper terminals shorted with pure copper.
That's crazy.
There's nothing crazy about it. The micro-climate inside a closed room
reacts to small temperate difference (and your exhaled breath is warmer
than room temperature) by creating convection currents which act to
reduce the temperature differences. I once had to put draft shields
(cylinders of paper) around a sensitive weighing head when I was testing
it in the lab.
<snip>
Do the math.
What's the Seebeck coefficient of a copper-copper junction?
On Thu, 13 Aug 2026 21:52:29 +1000, Bill Sloman <bill.sloman@ieee.org>
wrote:
On 13/08/2026 4:45 am, someone wrote:
What was the failure? Open contacts?
Seems the main problem is the excessive research required to select the
most appropriate relay for the application, and to verify the attributes >>> of the received batch before use. You can hold back a representative
sample for long-term testing in anticipation of a future recall.
Presumably you are reacting to John Larkin's original post.
He won't know why he thinks his reed relays failed. He probably managed
to try to make them break contact while in series with an inductor,
which can weld the contacts together.
The users told me so. Thus was a big liquid helium temperature and
level measurement system at the JeffersonLabs/CEBAF electron
accelerator. The reeds tended to fail open.
The usual failure mode is that the contact resistance gets too high.
Each make and break roughens up the contact area and eventually the
conducting area present when the contacts are closed is too small.
They typically offer 10 million operations
10 million is a pretty small number.
Mercury wetted relays don't have that problem, and last about ten times
longer than dry-reed relays, but their contact resistance also rises
with repeated cycling.
Reeds are absurd. Some people seem to have obsessions with them.
On Wed, 12 Aug 2026 18:45:02 +0000, someone <2a59d59e3809f827ce709d3815e3950eef4a6a93af5557a93a7fdfba71460843@example.com>
wrote:
There are shielded versions available, mainly to achieve high density interference free mounting, but the benefit extends to any nearby hazard or victim component.
https://cototechnology.com/library/datasheet/cotoclassic-9091-9092-series-reed-relay-datasheet.pdf
Note the 0.5msec total operating time that includes bounce.
It would be rare for the manufacturer to use different metals across mating contacts, especially for relays intended for instrumentation applications. The two metals actually used are to make a single contact. That would be something like an iron alloy for the reed itself and then a low-contact-resistance material like Rhodium plated at the contact point. Since the two contacts are identical, the thermocouple voltages cancel. But things can happen the disrupt that symmetry and EMF cancellation: (from AI)
Fritting and Micro-Arcing (Electrical Stress): If you switch a signal that has slightly too much voltage or current, a tiny electrical spark or a microscopic "fritting" event occurs right as the blades touch. This creates a localized burst of heat on just one side of the contact face. This microscopic temperature imbalance breaks the symmetry, generating a brief thermal voltage spike across the contacts.
Peltier Heating (DC Current Bias): If you continuously pass a relatively high DC current through the closed contacts, the Peltier effect will naturally pump heat from one blade tip to the other. This creates a permanent temperature difference between the two halves of the contact interface, forcing the contact point to act as an active thermocouple.
And those application-specific problems can appear regardless of the manufacturer's advertised low contact EMF.
EMF problems that people are mostly seeing are the thermocouples at the junctions of component leads/posts and the copper traces on the PCBs. This is again symmetrical, but proximal and asymmetrical heat sources, even the relay coil heat itself, can disrupt the cancellation.
It's hard to believe you can have low signal failures with the reeds advertised for instrumentation applications. There are all kinds of things that destroy the performance, and it's mostly bad manufacturing or mishandling: (from AI)
Micro-Cracks in the Glass Seal: If the glass-to-metal seal gets a microscopic crack during manufacturing, shipping, or soldering, the inert gas will leak out and oxygen will leak in. Once air is inside, the blades will begin to oxidize, causing the classic low-voltage connection failure.
Organic Outgassing Contamination: If the manufacturing facility is not 100% sterile, trace amounts of organic compounds or cleaning solvents can get trapped inside the glass capsule before it is sealed. Over millions of cycles, the physical impact of the blades can cause these trapped organic molecules to break down into a thin polymer film right on the contact point, blocking low-voltage signals.
Right. Real relays can have redundant contacts with some wiping
actions. A micro-inch of contamination can insulate reeds.
Plating Flaws: If the sputtered rhodium or ruthenium plating peels or blisters off the underlying nickel-iron blade, the raw base metal is exposed. This can cause erratic contact resistance.
Mechanical Shock Damage: Dropping a reed relay can slightly bend or misalign the internal blades. If the magnetic field from the coil can no longer pull them together with enough physical force to flatten out the microscopic contact points, contact resistance will spike.
The Coto part is about $4.50 for SPST.
Some reeds switch fast, but twang for milliseconds.
How does the solder bridging that junction come into play?
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