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Reading Applied Voltage in 4 Wire Mode

Models 2400, 2401, 2410, 2420, 2425, 2430, 2440, 6430
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frankzhao47
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Reading Applied Voltage in 4 Wire Mode

Post by frankzhao47 » November 27th, 2013, 10:17 am

Hello everyone,
On the Keithley 2400 in 4-wire sense mode while sourcing voltage and measuring current, is there a way to measure the actual applied voltage (instead of the (commanded) voltage across the Sense leads), short of connecting another multimeter? I've tried playing around with different commands in the default LabVIEW drivers, as well as the instrument settings on the front panel of the SMU. So far, all measured voltages are across the Sense leads.

Thanks a lot!
Best regards,
Frank Zhao

Dale C
Keithley Applications
Keithley Applications
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Re: Reading Applied Voltage in 4 Wire Mode

Post by Dale C » December 3rd, 2013, 1:33 pm

Hi Frank, you are referring to SOURCE READBACK.
:SENSE:FUNCTION 'VOLT'
That should do it.

frankzhao47
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Joined: November 27th, 2013, 9:29 am
Country: United States

Re: Reading Applied Voltage in 4 Wire Mode

Post by frankzhao47 » February 16th, 2014, 11:09 am

Hi Dale,
Thanks for the reply - I really appreciate that. I tried the Sense:Function 'Volt' command, and looked through the manual. It looks like the instrument returns the voltage currently on the Sense voltage leads, not the Input/Output leads.

To clarify, what I want is the following: A voltage is sourced through two 10kOhm resistors in series, in a test circuit. The Sense leads is connected parallel to one of these resistors. The 2400 is configured in 4-Wire Mode, at 5mV commanded voltage, so the output voltage source must be at 10mV. Using the Sense:Function 'Volt' command, the machine is returning 5mV across the Sense leads, never the 10mV across the Source leads. Is there a way to read the applied voltage (10mV in this case) instead?

We are measuring some very nonlinear electrochemical devices where the resistance effectively changes with voltage and time, so it would be nice to know what voltage is applied as well as the actual voltage drop across the device.

Thanks!

Andrea C
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Re: Reading Applied Voltage in 4 Wire Mode

Post by Andrea C » February 19th, 2014, 6:37 am

Hi Frank,

Think of it this way: the measured voltage is used to feedback to the SourceMeter to control the requested source voltage. The sense lines do not provide an independent voltage monitoring channel.

In your description of the two resistors in series, if you do not connect the sense lines and operate the SourceMeter in 2-wire mode, then you would read back the total voltage across the two resistors.

Keep in mind that the maximum difference in potential between the HI and the Sense HI is 5 volts, so take care if you place the sense lines across a portion of a voltage divider.

Andrea

sanjoy
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Re: Reading Applied Voltage in 4 Wire Mode

Post by sanjoy » December 1st, 2018, 4:03 am

I would like to do 4-probe measurement using 2400.for example (similar to previous one), Source terminal applies voltage across 3 1Kohms resistors connected in series and sense terminal should measure the voltage across the middle resistor. Is this possible with single SMU?

Andrea C
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Re: Reading Applied Voltage in 4 Wire Mode

Post by Andrea C » December 3rd, 2018, 5:03 am

Sanjoy,

Not advised.

The sense terminals should not be thought of as completely independent “channel” from the force terminals.
When the 4-wire sense mode is enabled, the voltage is measured on those lines. If you command the SMU to source some voltage, it will use the value at the sense lines to know when it has accomplished the job. Meanwhile, the voltage at the force terminals will be different value if you have I*R potential between force and sense.

The I*R between force and sense must be less than 5V for model 2400.

For your three 1K resistors, you could try forcing current and measure voltage on middle resistor with sense lines. Assume you force 1mA into the total 3K ohms, the force lines will have 3V total, while the middle resistor and sense lines have 1V.
If there is any contact resistance, then force lines will see more than 3K ohms and voltage will rise. Take care about the max 5 volt delta.

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