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Keithley-3706 with 3721 switching card- 4wire measurements

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MartinaCA
Posts: 3
Joined: January 16th, 2018, 2:05 am
Country: Italy

Keithley-3706 with 3721 switching card- 4wire measurements

Post by MartinaCA » January 16th, 2018, 7:37 am

Hi,
Recently I have received Keithley 3706 with 3721 switching card. I want to perform two-wire and four-wire resistance measurements. For two wire resistance measurements it works fine. I don't understand how to perform the four-wire resistance measurements.

From the User's manual I know that for 4-wire resistance connections on a 40-channel switching module, channels 1 through 20
(which are used as the INPUT terminals) are paired to channels 21 through 40 (which are used as the
SENSE terminals). I opened the 3721 switching card: channel 1-20 are connected with a wire to channel 21-40. I disconnect channel 01 with 21 to use these channels as 4-wire probing.
I set, from front panel, function "4wireResistance" to Channel "1001". I close Channel "1001" ( also paired channel 1021 is automatically closed).
My DUT is a 1 kOhm resistor. The output measurement is around 0.2 Ohm. It seems an internal resistance ( as short circuit).
I don't understand the problem.
Thanks in Advance for replies.
Regards,

Martina

Andrea C
Keithley Applications
Keithley Applications
Posts: 1280
Joined: October 15th, 2010, 10:35 am
Country: United States
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Re: Keithley-3706 with 3721 switching card- 4wire measurements

Post by Andrea C » January 17th, 2018, 7:45 am

Can you clarify about the connections?
When you say you opened the switching card, what does that mean?
The 3721 has two DB50 connectors. Do you use the 3721-ST accessory? Or do you have custom cable to the DB50?

For the channel paring for the 4-wire ohms, make sure the HI of each channel and the LO of each channel are pared together:
3721_4Wire_Ohms.PNG
3721_4Wire_Ohms.PNG (45.64 KiB) Viewed 9212 times

MartinaCA
Posts: 3
Joined: January 16th, 2018, 2:05 am
Country: Italy

Re: Keithley-3706 with 3721 switching card- 4wire measurements

Post by MartinaCA » January 17th, 2018, 12:36 pm

Thank you very much for the reply. I’m sorry for the inaccuracies, but I’m not familiar with this type of instrument.

I use, as you say, the 3721-ST screw terminal. I attached the photo, which shows the connections between the paired channels (1001-20 with 1021-40).
I opened it and I removed the connection (wires HI and LO) between channel 1001 and channel 1021. I connected new long wires ( black and red wires, at right on the photo) to channel 1021 to use it with channel 1001 for the 4-wire resistance measurements.
IMG_3721ST-min.jpg
IMG_3721ST-min.jpg (1.03 MiB) Viewed 9197 times
Thank you,

Martina

Andrea C
Keithley Applications
Keithley Applications
Posts: 1280
Joined: October 15th, 2010, 10:35 am
Country: United States
Contact:

Re: Keithley-3706 with 3721 switching card- 4wire measurements

Post by Andrea C » January 22nd, 2018, 5:06 am

It seems everything you do is fine.
The channel pairing for four wire connections at channel 1 on the 3721-ST are with the highlighted channels:
3721-ST_4wire_channel_pairing.PNG
3721-ST_4wire_channel_pairing.PNG (76.37 KiB) Viewed 9089 times
The HI of each (channel 1 and 21) should be connected to one side of DUT; the LO of each connected to other side.

On front panel of 3706A, press Open All.
Press Config and Chan. Scroll to DMM Config and set for 4wireohm.
Press Close. This should close channel 1001 and 1021.
Press Trig button to acquire and display a 4wireohms reading.
Verify which channels are closed: press Display button until it shows "Closed Channels". Confirm 1001 and 1021.

If still no good, maybe independently verify 2 wire ohms on each channel separately.
Or do four wire ohms on channel 1002 and 1022.

MartinaCA
Posts: 3
Joined: January 16th, 2018, 2:05 am
Country: Italy

Re: Keithley-3706 with 3721 switching card- 4wire measurements

Post by MartinaCA » January 24th, 2018, 10:46 am

Thank you for your reply. I tried to do different tests with channel 1001/1021 (no more connected, as I told you before). I used a 330 Ohm resistor as a DUT.

1. I set 2-wire ohm function to channel 1021 (closed channel 1021). It works. I measured 329.8 ohm
2. I set 2-wire ohm function to channel 1001 (closed channel 1001). It doesn’t work. I measured 0.44 ohm. If I do a short circuit with LO and HI wires of channel 1001 and set 2-wire ohm function I measured 0.37 ohm.
3. I set 4-wire ohm function to channel 1001 (closed channel 1001 and 1021). It doesn’t work. I measured 0.288 ohm
4. I set 4-wire ohm function to channel 1021 Error state “Configuration error function mismatch in configuration specified”

I tried with channel 1004/24, without eliminating the connection wires ( so I have two channels, which have four wires inside the screw terminal, but only 2 wires out of the screw terminal and I used my 330 ohm resistor as DUT ).

1. I set 2-wire ohm function to channel 1024 (closed channel 1024). I measured 329 ohm
2. I set 2-wire ohm function to channel 1004 (closed channel 1004). I measured 0.44 ohm, the same value of channel 1001.

I think that channels from 1001 to 1020 don’t work properly.

Thanks in advance.
Regards,

Martina

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