Identifying coto relay from teradyne board - Page 1
Forum section: electronics / general

author: sahko123
author_rank: Frequent Contributor
timestamp: April 13, 2022, 03:45:07 pm
content: I recently pulled a load of relays from a teradyne board along with some 0.05% resistors of various value. I can't find the exact data sheet for the 581-145-00 coto relays shown below. The data sheets I find seem to be for different relays entirely.Does anyone have the data sheet or more info on these relays?

author: Gyro
author_rank: Super Contributor
timestamp: April 13, 2022, 04:20:18 pm
content: It looks like a Mercury wetted reed relay - it has a vertical orientation mark.

author: sahko123
author_rank: Frequent Contributor
timestamp: April 19, 2022, 09:38:53 am
content: Why are they mercury wetted? Are there similar coto relays with datasheets?

author: wraper
author_rank: Unknown
timestamp: April 19, 2022, 09:43:47 am
content: Quote from: sahko123 on April 19, 2022, 09:38:53 amWay more reliable, no arching. Makes a reliable contact straight away, no bounce. No need for wetting current.

author: sahko123
author_rank: Frequent Contributor
timestamp: April 19, 2022, 09:55:43 am
content: Ah right so the mercury is essentially used as a "resistor" across the contacts? Whats generally the purpose for these relays. I was assuming that they'd be low leakage types but it seems its actually the opposite.

author: wraper
author_rank: Unknown
timestamp: April 19, 2022, 10:04:57 am
content: Quote from: sahko123 on April 19, 2022, 09:55:43 amNo, There is no leakage. Contacts are wetted by mercury, therefore closed contacts are covered in liquid metal.https://www.celduc-relais.com/en/reed-switches/Quote

author: sahko123
author_rank: Frequent Contributor
timestamp: April 19, 2022, 10:09:48 am
content: Ah so its more of a soft switch mechanism rather than being filled. So are they just designed to last long? What are they normally used in?

author: MK
author_rank: Regular Contributor
timestamp: April 19, 2022, 12:45:18 pm
content: It is two-fold, the lack of bounce is important for some measurements, the long life is a bonus for others

author: Gyro
author_rank: Super Contributor
timestamp: April 19, 2022, 01:00:13 pm
content: Three fold... having no minimum switching current or voltage requirement.P.S. "soft switch" isn't really the correct term - Tektronix used them for very fast rise time pulse generators (in the 4ps range). It's the lack of bounce that is important.A forum search for 'mercury wetted relay' will reveal lots of posts.

author: TimFox
author_rank: Super Contributor
timestamp: April 19, 2022, 01:52:51 pm
content: The vertical orientation is very important: I use DPDT mercury relays for low-level audio and, when inverting the box on the test bench, the mercury flows from the small reservoir and bridges all the contacts. This reverses without damage when the relay is back to the correct orientation.

author: sahko123
author_rank: Frequent Contributor
timestamp: April 19, 2022, 03:10:02 pm
content: Ah so the no bounce would produce a damn near vertical rise time privy to parasitic capacitance and inductance of course. Or is there more to it than that to make a super sharp rise time?

author: TimFox
author_rank: Super Contributor
timestamp: April 19, 2022, 03:29:29 pm
content: A good mercury-relay pulse generator uses careful construction with transmission lines to make a good pulse rise-time into a matched load.They are commonly used in nuclear spectroscopy using "multi-channel analyzers" that produce a histogram of pulse heights from scintillators or solid-state detectors, to calibrate the ADCs.Adding a shorted transmission line stub will produce a finite-length pulse.

author: 1audio
author_rank: Frequent Contributor
timestamp: April 19, 2022, 04:48:13 pm
content: Studying the docs for this:https://w140.com/tekwiki/wiki/109will give you a good insight into building a relay pulse generator. Its not simple but possible. 250 pS and 300V is pretty impressive. Manual:https://xdevs.com/doc/Tektronix/TEK%20109%20Instruction.pdf

author: Bill158
author_rank: Regular Contributor
timestamp: April 19, 2022, 11:07:32 pm
content: I worked 25 years for an ATE (Automatic Test Equipment) tester manufacturer. We built ATE for testing descrete semiconductors such as diodes, transistors, FETs, and most 2,3 and 4 leaded devices of that type. Our equipment was capable of testing a 2n2222 for 13 parameters in about 100 ms. So we could test 10 devices per second, save all results if dataloging was set and issue the necessary Binning information to a handler, wafer prober or just an operator for hand testing.We used mercury wetted reeds (relays) in this equipment for one simple reason. They last for hundreds of millions or even billions of cycles. Dry reeds fail way too soon in this type of operation! So each test type requires changing the connections of programmable power supplies, measurements such as voltmeter, amp meter, peak detectors to each lead of say a transistor or FET. We covered all test types required and specified in data sheets. BVCEO, VDSP, HfeDC, HfeAC and on and on. We had probably at least 600 or more mercury wetted reeds and relays in each system. Some reeds were enclosed in a package similar to what you have shown but sometimes 4 in each package. Others were inside open coils because of leakage concerns. We could measure down into the sub-pico amp range. Our electrometer went from 100 pA full scale to 100 mA full scale in decade ranges. The resolution was 4 3/4 digits (16 bit ADC). We could use a 6.5 digit DVM if requested and even 8.5 digits (HP/A/K 3458A DVM) as options. You are showing a Teredyne packaged single mercury wetted relay in your picture. Teredyne was one of our competitors. The relay was probably made for Teredyne using their specs by COTO. We used various mercury wetted reed manufacturers but mainly Gunther when I was there. Using open coils with mercury reeds through them we sorted the IR (insulation resistance) to grades of 10 e13 ohms resistance and higher. Clean glass which enclosed the reeds was necessary to get this resistance. It took a lot of effort to clean the boards with open frame reeds. We used FREON until it was outlawed and then DI (de ionized) water cleaning afterwards. The voltage rating when the reed was open would have to be as high as 2000 volts in some cases. Very difficult to achieve and the relays and reeds would have to be sorted accordingly during incoming inspection. You ask what these would be used for? Just one example.Bill

author: Bud
author_rank: Super Contributor
timestamp: April 19, 2022, 11:29:30 pm
content: Back in old good times they were used in Ham rado tube transmitters for CW (Morse code) manipulation.