Well, since you blessed them the Omron relays are in the design now instead of the reeds :-)
To my surprise Eagle already had a model for the G6K-2P-Y.
-- Regards, Joerg http://www.analogconsultants.com/
I'm not kowtowing to your obvious brilliance? Produce some brilliance and I'll kowtow to it. Produce nonsense and I'll tell you it's nonsense.
If you find dry reed relays to be unreliable, you aren't being careful enough to protect the contacts from excessive currents or voltages. That you don't understand this is a bit odd. That you don't want to understand this is rather less surprising.
I've done quite enough work with reed relays - admittedly a long time ago - that I do happen to know what I'm talking about. You may have mis-used more of them but you seem to have drawn the wrong conclusion
- reed relays are unreliable - from your occasional mistakes. The right conclusion would have been that even John Larkin can get it wrong, but you've got an aversion to recognising that.
Your loss.
The last ones I designed in were range-changing mercury wetted reeds on the Cambridge Instruments EBMF 10.5. They worked exceptionally well. The machine cost a million dollars or so, and Cambridge Instruments might have sold 12 in a good year - they never did better than a good six months when I was there.
If the reeds are bending, the area in contact is going to be changed by the differential movement. The mercury film between the contacts has to move around to accommodate this and it's viscosity damps the movement and turns the translational energy into heat.
But Pickering still lists them - series 88 and 89
and even Newark will supply a Coto part - albeit it at an extravagant price, and only in extravagant volume
They were never cheap, high-volume, parts but "super-expensive" is wrong. Newark isn't the place to buy that kind of product.
Sorry about that. I should have noticed. I can't say I like the warning about storage in a contaminated atmosphere degrading the contacts. The nice thing about reed relays is that the contacts are hermetically sealed behind a vacuum-tight glass-to-metal seal.
-- Bill Sloman, Nijmegen
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, sObviously. You didn't learn anything like as much as you should have done to get your undergraduate degree, and you wouldn't have been able to get away with that as a post-graduate student.
True. But they do teach a lot of stuff that circuit designers find useful. You can learn it without going through the relevant undergraduate courses - I did - but then you have to make your way through the relevant text-books without the help of a lecturer or two to keep your mind on the job.
Sure. RSI show-cases a lot of what physicists do wrong when it comes electronic design and development, which is basically that they don't bother searching the literature and re-invent stuff without getting it entirely right.
As a graduate student I did search the instrument literature, but this was seen as odd behaviour.
And designing something that's only got to work for long enough to generate a paper's worth of results in the hands of highly motivated graduate student isn't a good background for designing stuff for production - even small-scale production.
Sounds good. At Cambridge I had access to the University libraries by virtue of joining the Cambridge Philosophical Society, which is why a lot of people join the Cambridge Philosophical Society, but that was before down-loading was entirely practical.
-- Bill Sloman, Nijmegen
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I suspect that reeds are more reliable *if* they work at higher currents and voltages. The troubles I've had with them were mostly low-level analog switching where there were no significant currents or voltages available at all. The symptoms are stuck contacts (metallurgical bonding?) and high impedance closures.
Did you work with thousands of them? I have, and I won't again.
You may have
Loss? The DPDT telecom relays are smaller, cheaper, surface mount, multi-sourced, need less coil power, have lower thermal EMFs, and are far more reliable.
So if those reeds had a 0.1% failure rate, you might not have seen it.
Where is that warning? The Fujitsu, Omron, and NEC parts are all epoxy sealed. We solder/reflow/wash without problems. If we had gigohm-level leakage, we'd know it.
-- John Larkin Highland Technology, Inc jlarkin at highlandtechnology dot com http://www.highlandtechnology.com Precision electronic instrumentation Picosecond-resolution Digital Delay and Pulse generators Custom laser drivers and controllers Photonics and fiberoptic TTL data links VME thermocouple, LVDT, synchro acquisition and simulation
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fSounds crazy. When we had trouble with mode hopping at Fisons Applied Sensor Technology - because it changed the direction of the laser beam, and thus the angle of incidence of the beam on the surface being interrogated, which we were monitoring to about one second of arc - we just went over to a single mode laser diode and stabilised it's temperature well enough that it always stayed in the same mode.
So where do they get published? The British Journal of Scientific Instruments - now Measurement Science and Technology - got some of R.V. Jones papers, and Blackett's as well. Today the journal isn't quite so mind-numbingly academic as RSI, and the refereeing is marginally better, but they still publish the usual proportion of trivial rubbish.
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n s n mYou need noble-metal plating on the contact area for low current - "dry" - operation. Rhodium, rhenium or iridium, usually on top of a thicker layer of gold. Power relays use very different contact materials and need a minimum "wetting" current.
If you didn't know enough to specify the right contact materials for the current level you were working at, it isn't altogether surprising that the relays that you bought didn't work reliably in your application
If at first you don't succeed, give up, rather than finding out what you did wrong ...
Only in a "non-contaminating atmosphere" if the data sheet is anything to go by.
There were four per scan board, and two scan boards per machine (X and Y) machine, and Cambridge Instruments might have sold a hundred systems before they took over the Philips EBMF - which had been designed from the ground up in the late 1980's rather than evolved from a 1970's electron microscope ...
They'd have had an even chance of seeing a 0.1% failure rate, and a
100% chance of hearing about it if one failed. It was a million-dollar machine, and the customers did recover their investment - the acceptance test of the first one sold was to produce a couple of wafer's worth of GaAs RF mosfets and somebody worked out that the retail value of the parts produced to get acceptance was rather more than the price of the machine. y=3Dm...
sTry reading the data sheet.
It's half-way down page 8 of the pdf, page 60 on the page, under "precautions".
Stuff diffuses through epoxy - admittedly hydrogen and helium do diffuse through glass but at leas they don't screw up the contacts.
It's about contact resistance when the contacts are closed, not leakage when the contacts are open.
-- Bill Sloman, Nijmegen
What ever happened to MEMS relays? They were hot stuff for a while. All sorts of people promised me samples that never arrived.
Here's one: $210 each, stock 0.
It can switch half a mA at half a volt.
-- John Larkin Highland Technology Inc www.highlandtechnology.com jlarkin at highlandtechnology dot com Precision electronic instrumentation Picosecond-resolution Digital Delay and Pulse generators Custom timing and laser controllers Photonics and fiberoptic TTL data links VME analog, thermocouple, LVDT, synchro, tachometer Multichannel arbitrary waveform generators
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And that in a nutshell is exactly why they never took off. The physical dimensions makes for very limited carrying current and very limited contact operating voltage.
Possibly useful for switching some video and similar LV switching, especially where high isolation is required.
?-)
Just noticed this quote from your link, John. It says that mercury wetted relays are for "applications where the mercury eliminates contact bounce." It's your own link, yet it contrasts at least somewhat with your earlier comment just above the link.
Jon
I've been perusing the Omron G6K relay series datasheet. I like it, but I worry about RF characteristics. I worked out the open contact capacitance to be about 160fF. It may be half that, depending on how they got the HF isolation plot; They don't say.
I haven't found anything concerning coupling or capacitance between the two poles in these relays. Would you have some measured figures to share?
(I ordered a few to find out...)
Thanks, Jeroen Belleman
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And yet for some reason, they are used exclusively in high end DMM switching circuits (Keithley 2000 series, Agilent 344XX series, and even the Agilent 3458A). Not sure why, but they must be good for some applications.
Minor correction: I should not have stated exclusively, as there are a few latching types used as well.
Video routers I've worked with were mostly reed relay, and used an Amphenol coaxial transfer relay to swap the normal & preview outputs. That let you set up a special configuration, then switch back to normal operation. Early video routers weren't tied to the video sync, and were useless for color studios. They went away, when good analog switches became available.
Just threw a G6JU (which I use for LHe and sub-1K stuff) into Agilent E5061 with the 16092A fixture. It showed ~0.95pF for an open contact and ~15nH for a closed contact. The closed contact resistance was maybe 10 mohms (less than resolvable) at low frequencies, increasing to 2 ohms at 500MHz.
Regards, Mikko
No contradiction. The mercury eliminates contact bounce but doesn't eliminate twang. The reeds still vibrate after closure, making low-level electrical noise in the magnetic field, but the contact gap remains closed by the mercury.
All em relays will twang to some extent. In my experience, reeds do it a lot.
There's no good reason to use reeds when much smaller, cheaper, surface-mount, more reliable, lower coil power, standardized parts are available.
-- John Larkin Highland Technology Inc www.highlandtechnology.com jlarkin at highlandtechnology dot com Precision electronic instrumentation Picosecond-resolution Digital Delay and Pulse generators Custom timing and laser controllers Photonics and fiberoptic TTL data links VME analog, thermocouple, LVDT, synchro, tachometer Multichannel arbitrary waveform generators
Maybe for t-ohm leakage? Their long dimension helps there, assuming you keep the coil contacts away from the signal.
Seems like the thermals would be a problem in a DVM. We use the Fujitsu latching relays in thermocouple applications.
-- John Larkin Highland Technology Inc www.highlandtechnology.com jlarkin at highlandtechnology dot com Precision electronic instrumentation Picosecond-resolution Digital Delay and Pulse generators Custom timing and laser controllers Photonics and fiberoptic TTL data links VME analog, thermocouple, LVDT, synchro, tachometer Multichannel arbitrary waveform generators
Thanks Mikko,
From the specified 60dB of isolation at 10MHz I'd expect some
320fF between open contacts. The figures don't match. How did you mount it?Jeroen Belleman
Here is a picture of the insides of my Keithley 6517A electrometer.
The red tubes are coto reed relays, special types with ultra-high insulation resistance and screening. There are also some conventional NEC relays, seem to be the style you like.
Also note the sticking up thing with the meandering track. It has 1T written on it...
-- John Devereux
Back in the dark ages (1980...) I worked in the office where they had just installed an EAX2 switch. Thousands of reed relays to do the switching of telephone calls, in boards with about 20-40 relays on each. They had special test gear to take the bad boards, and tell them which relays had gone bad. Automated testing told them which boards had gone bad. It was a small switch, just two 'exchanges,' and they typically had 10-20 bad boards to test a day...
Those guys just LOVED reed relays... NOT!
Charlie
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