DIY Low Thermal EMF Switch/Scanner for Comparisons of Voltage and Res. Standard

[zlymex]

1. Why Switch/Scanner
Comparison of standard(voltage/resistor) is precise, repeatable, low Thermal EMF.
Comparison can be easily made automatic.
Multi-reading results make statistics/averaging at ease and achieve high confident level.
Standards to be compared may be relatively permanently connected thus inconsistency due to contact variation is greatly reduced.
May compare multi-standard(ex. up to 16 or greater) for a long time.
Derived use i.e. measurement of temp-co.


2. Why DIY powerless Switch/Scanner
Very simple to use. No programming, no GPIB.
Powerless, and therefore no direct interference from the mains.
Powerless, and therefore very little heat generated and less Thermal EMF.
Compact, low cost.
No power switch, consume virtually no power when idle.

[zlymex]

3. Features and Principles of the DIY switch
Provide 2*2(DPDT) or 4*2(4PDT) switch, or 2*4, 4*4, 2*8, 4*8, 2*16, 4*16 switch.
MC control(Multi-meter Measurement Complete Signal).
MC power supply, consume about only 0.3mA current.
Use 74HC CMOS and related low power IC.
Use Latching relay to achieve low power consumption.
Manual switch and free running mode provided.
Operates in loop manner only.

MC or VMC signal is usually provided by precision multimeters as a standard feature.
It usually stay logic high when idle or during measurement, and goes to logic low briefly when a measurement is complete.

When measurement by the multimeter is complete, it's the perfect time for switch/scanner to operate.

Newer multimeters use CMOS IC for VM output thus the high level is nearly 5V. Old ones such as my Agilent 3458A (made in 2006) uses TTL IC which gives only 3.65V when drawing 0.5mA current. However, this is enough for the switch to operate properly.

Although is mechanical, the relay will complete it's switch over in less than 5ms, plus settle down of the measured V or R, which normally within the default delay time of a typical multimeter. For 3458A 10V range NPLC=50, default delay is 10ms. This delay may be increased if needed.

[zlymex]

4. Schematic of My first 4*2 switch for two standards(V or R) comparisons


The Latching relay, Omron G5AK-237P





Omron G5AK-237P, DPDT low signal double-winding latching relay.
Data sheet is here http://datasheet.octopart.com/G5A-237P-DC5-Omron-datasheet-109999.pdf


The Drive
Normally the set or reset coil operate at 5V individually.


However, the set and reset coils are identical and can be connect in series or in parallel. When in series, it also operate at 5V but consume half the current.


When paralleled. it will operate at 2.5V but the current will be doubled. This is the way I use.



Power supply



I use HT7136 low dropout CMOS low power regulator. Connect a 200 Ohm resistor and a Schottky diode to VM, and output is 3.5V minimum through the use of a 470uF filter capacitor.
DS of HT7136 is here: http://www.holtek.com/pdf/consumer/71xx_1v170.pdf

The Principle is straight forward, every time a measurement is complete, VM goes low briefly toggle the J-K flip-flop and hence the relay.


Optional trigger is also provided for manual momentarily switch K or by activating the free running astable vibrator.

[zlymex]

5. Implementation and testing
Breadboarding first


Then assemble the device on universal board




Cat. 5 twisted pair, pure copper and screened, good for this purpose.





Test is performed by making measurements of two inputs alternatively


Sampling is done by another DIY interface device:




One end of the device is connect to multimeter GPIB, another end is connect to PC's USB port by a RS232-USB converter(early version) or direct USB connection(later version). This device is designed by llycom and is widely used among Chinese volt-nuts.

By running the dedicated program, one can send any GPIB command to the multimeter.




It also provides a precision temperature sensor(DS18B20).

The final graph is the test result when two inputs shorted. Ideally the dark blue line and purple line should be equally flat to zero but it's not owing to multimeter's noise and offset. However, the average of the two lines are quite the same with less than 5nV difference, well below the noise level of 3458A.

[zlymex]

6. Next version of the 2*4 switch

First 8 photos show the implementation of PCB version by Mytek, last 4 photos show the miniature version.

[zlymex]

7. 17*2 scanner for up to 17 voltage standards comparisons

[zlymex]

8. 16*4 scanner for 4 wire standard resistors comparisons

believe or not, 32 latching relays and it's related circuitry power by multimeter VM and consume as little as 0.2mA (When 3458A choose NPLC=50 and AZ on)

[zlymex]

9. Application examples

By applying very stable 100mA current thr two one-ohm resistors, 3458A reads two 100mV alternatively thus will compare to sub-ppm level.


Compare two 10V.
Blue line: 3458A measurement of a 10V standard (Warming up curve)
Red line: difference of two 10V standard plus 10V.


Standard resistors comparison chart and photo.



For those who can view 38hot.com properly, I have other scanner related topics:
Mechanical switch http://bbs.38hot.net/thread-1006-1-1.html
Overview of metrology scanners http://bbs.38hot.net/thread-1016-1-1.html
Data Proof 160A Scanner, Principle and modification http://bbs.38hot.net/thread-1082-1-1.html
DIY 16ch Powerless Scanner for Voltage http://bbs.38hot.net/thread-3658-1-1.html
DIY 16ch*4wire Powerless Scanner for Standard Resistor Comparisons  http://bbs.38hot.net/thread-4041-1-1.html
Precise measurement of alpha/beta temp-co of SR104 standard resistor http://bbs.38hot.net/thread-1352-1-1.html
DIY 100mA constant current source for comparison of 1 ohm standard resistor http://bbs.38hot.net/thread-17593-1-1.html
Tests on 7V and 10V voltage standards http://bbs.38hot.net/thread-645-1-1.html


<The End>

[quarks]

Great work, thanks a lot for sharing

Here is one of my scanner cards for Keithley 7001 with very nice COTO relays (see att. pic.)

on Reply #2 unfortunately I cannot see your pictures
edit: now it is the same on other replys also

on Reply #3 Where did you get the spade lugs?

on Reply #7 SR104-1, 742A + VHP101 look flat as expected, but what is the jump 11y/2W?

[zlymex]

Thanks quarks, that's is a very good switch board. My approach is to generate less heat to compensate not-so-good relays.

Reply #2 I see the photos fine, both reply #2 and others.

Reply #3 those spade lugs was a custom made group-buy in China, pure copper, later I changed to lugs with gold flashed.

Great work, thanks a lot for sharing

Here is one of my scanner cards for Keithley 7001 with very nice COTO relays (see att. pic.)

on Reply #2 unfortunately I cannot see your pictures
edit: now it is the same on other replys also

on Reply #3 Where did you get the spade lugs?

on Reply #7 SR104-1, 742A + VHP101 look flat as expected, but what is the jump 11y/2W?

[quarks]

Hello zlymex,

here is what I see (see att. pic.)


Those spade lugs look very good. Is it possible to buy some?
They would be a great addition to my
https://www.eevblog.com/forum/buysellwanted/diy-low-emf-cable-and-connectors/msg190302/#msg190302

[zlymex]

Hello zlymex,

here is what I see (see att. pic.)

Those spade lugs look very good. Is it possible to buy some?
They would be a great addition to my
https://www.eevblog.com/forum/buysellwanted/diy-low-emf-cable-and-connectors/msg190302/#msg190302

I see your reply pictures fine, but I don't know why my pics won't show up on your side.

Those spade lugs was bought 5 years ago and I was a group buy participant. Usually the seller will be long gone.

lly/2w is the DIY two-wire  standard resistor by llycom sent to me for test. I cannot recall what's inside as I did not open it for photo. I guess it's a single VHP101-10k.
Because it's two wire, there is a value jump when I disattach and reattach the lugs from the binding post during test.

btw, My VHP101 DIY consist of 4 matched resistor elements.

[quarks]

now I know it is IE, because with Operea I can see your pictures (still wonder what the cause is)

btw, My VHP101 DIY consist of 4 matched resistor elements.

Very nice!!!
Have you used 4x 10k values (2 in series and than same in parallel) or did you use 4x 40k in parallel?

[zlymex]

now I know it is IE, because with Oprea I can see your pictures (still wonder what the cause is)

btw, My VHP101 DIY consist of 4 matched resistor elements.

Very nice!!!
Have you used 10k values (2 in series and than 2 parallel) or did you use 4x 40k in parallel?

Here is the large photo with resistor values on it, 9k999.
Mine is 4 wire(actually it's 6 wire), but llycom's 2 wire.

[zlymex]

Talking about matched resistors, I selected the 4 from a batch of 40.

2 resistors may match alpha temp-co, it usually takes 4 to match beta as well.

[quarks]

Here is the large photo with resistor values on it, 9k999.

thanks again

Your board looks like ceramic. Can you share some details?
When I did some home work for a "as good as possible" DIY resistor reference, I bought some ceramic solder stands (see att. pic.).
I hope with this stands, it will be possible to also build high resistance values (I plan 1GOhm). Have you tried high resistance values also?

[zlymex]

thanks again

Your board looks like ceramic. Can you share some details?
When I did some home work for a "as good as possible" DIY resistor reference, I bought some ceramic solder stands (see att. pic.).
I hope with this stands, it will be possible to also build high resistance values (I plan 1GOhm). Have you tried high resistance values also?

Ceramic solder stands is a very good idea as I bought some as well.
I use Teflon board in hope it's better insulation. However IMO, ceramic is good enough for 10k even for sub-ppm level requirement.
For higher resistor value such as 1GOhm, still good if precision not exceed 0.01% and keep the surface dry and clean.
I tried even higher values like 10GOhm and 100GOhm, guarding must be applied even the insulation is Teflon.
What resistor element you plan to use for 1GOhm?
I once use 100 Dale RN55D 10MOhm for 1G.

[quarks]

I use Teflon board in hope it's better insulation.

thanks, that makes it much easier to drill the holes

However IMO, ceramic is good enough for 10k even for sub-ppm level requirement.
For higher resistor value such as 1GOhm, still good if precision not exceed 0.01% and keep the surface dry and clean.

good to know

I tried even higher values like 10GOhm and 100GOhm, guarding must be applied even the insulation is Teflon.
What resistor element you plan to use for 1GOhm?
I once use 100 Dale RN55D 10MOhm for 1G.

Yes, guarding is a must for high resistance values (att. are some details from Keithley Low Level Meas. Handbook)

Until now I have bought OHMITE MOX 500MOhm (but only 1%), several Caddock USF 0.01% (but only 10MOhm, which will be extremly expensiv when I need 100 pieces) and I have a sufficient large batch of promissing Caddock MG745 40MOhm 0.1% on order.

[zlymex]

until now I have bought OHMITE MOX 500MOhm (but only 1%), several Caddock USF 0.01% (but only 10MOhm, which will be extremly expensiv when I need 100 pieces) and I have a sufficient large batch of promissing Caddock MG745 40MOhm 0.1% on order.

That's great
While I cannot find Caddock USF(or cannot afford), I bought 100+ used Caddock TF020R-3 20MOhm instead.

Another expensive option for 1G or 10G maybe Supper MOX(MOX910)

Your blue Omite is Mini-Mox, I also bought 20+ similar Slim-Mox 104 500MOhm for 1G and 10G.

[quarks]

Super MOX 910 looks also good

do you know by chance what is used in the Fluke 8508A-7000K calibration kit (see att. pic.)?

[Vgkid]

Well done.
This will be a rather interesting thread to follow.

[quarks]

OT: I indeed normally do not use IE with my private PCs.
But with my business PCs I am forced to use it, so sometimes I open eevblog with IE

[Mickle T.]

This idea has been widely used in the Prema DMMs. I used a similar scheme to control the sealed relay (RPS-25) in the selfcal module of the 8.5-dig. DVM.

[Andreas]

Hello Lymex,

thanks for sharing also from my side.

There are many good ideas in the cirquits.
Especially using the DMM trigger as power supply was a fact that
I could not see from the link on volt nuts to 38hot.com.

8. 16*4 scanner for 4 wire standard resistors comparisons

believe or not, 32 latching relays and it's related circuitry power by multimeter VM and consume as little as 0.2mA (When 3458A choose NPLC=50 and AZ on)

I guess it is only for resistors and not for reference voltages.
Or do you have a possibility to get into some "reset" state for the relays after "power on".

The bad news is that Mouser is saying that the OMROM G5AK-237P is "discontinued"    ...

But the good news is that I found an alternative relay, the Panasonic TX-S series  ::

I am using Panasonic/Matsushita TQ2 series (the TN2 series would work also) running for about 1-2 weeks from a 9V block including microprocessor.

With best regards

Andreas

[splin]

The bad news is that Mouser is saying that the OMROM G5AK-237P is "discontinued"    ...

But the good news is that I found an alternative relay, the Panasonic TX-S series  ::

I am using Panasonic/Matsushita TQ2 series (the TN2 series would work also) running for about 1-2 weeks from a 9V block including microprocessor.

With best regards

Andreas

Panasonic specify a minimum switching load of 10uA, 10mV which might be a problem for comparing references - but probably not for a few thousand or 10s of thousands cycles! They recommend the SX series for low signal levels but even those specify a minimum of 10uA, 1mV.

I know that they ran into this problem at a company I used to work for - minimum loads aren't always quoted for relays but some contact materials rely on the current disruption to clean the contacts.

I wonder if the contacts get noisy over time or just suffer increasing contact resistance?

Are reed relays better in these regards being hermetically sealed?

The thermal EMF spec is for the TXQ is 5uV and .3uV for the TX-S but those are for the non-latching parts. Are you using latching versions and if so have you measured the thermal EMFs (or tried - I guess it's quite tricky to do)?

Thanks,  Splin