Tektronix Technical Forums are maintained by community involvement. Feel free to post questions or respond to questions by other members. Should you require a time-sensitive answer, please contact your local Tektronix support center here.

2-wire and 4-wire Voltage measurements

Post Reply
Luigi_B
Posts: 9
Joined: October 26th, 2011, 6:36 pm
Country: United States

2-wire and 4-wire Voltage measurements

Post by Luigi_B » November 2nd, 2011, 10:33 am

Hello,

I am currently using a Keithley 2602A Source meter. I am running some efficiency sweep using Labview on a DC-DC converter. I have Channel A as the source and Channel B as the Load. I have both channels Measuring voltage and current: Channel A is in 4-wire and Channel B is in 2-wire. Channel A measurements are accurate(I confirmed this with some other digital multimeters), but Channel B voltages are not that accurate. Could it be that Channel B has to be in 4-wire? Would that affect the Channel B having it to be a load?

Thank you

-Luis

Nathan S
Keithley Applications
Keithley Applications
Posts: 254
Joined: February 28th, 2011, 6:17 am
Country: United States
Contact:

Re: 2-wire and 4-wire Voltage measurements

Post by Nathan S » November 2nd, 2011, 10:44 am

When you mention having Channel B be a load, do you mean that it is sinking current? If so, how much and what are your voltage readings compared to what you expect? I would expect that Remote Sense (4 wire) would help here as you would then remove the error term from the voltage dropped across your leads if in fact you have some significant current flowing in them.

Luigi_B
Posts: 9
Joined: October 26th, 2011, 6:36 pm
Country: United States

Re: 2-wire and 4-wire Voltage measurements

Post by Luigi_B » November 2nd, 2011, 11:02 am

Yes, I meant sinking current (which in my case, I just have negative currents through channel B), the currents were from 10mA to 500mA. As it was increasing from 10mA, I was expecting 1.2V at ChB but it reading 1.8V. I agree, I could be the voltage drop across the leads. I was not sure if having the ChB in 4-wire could affect its sinking current mode.

Nathan S
Keithley Applications
Keithley Applications
Posts: 254
Joined: February 28th, 2011, 6:17 am
Country: United States
Contact:

Re: 2-wire and 4-wire Voltage measurements

Post by Nathan S » November 2nd, 2011, 11:23 am

For sinking applications like using it as a load (in your case), it would be useful to Sink Mode as a benefit to accuracy (as well as remote sense). You can do this via the front panel by pressing Config -> SRC -> V-Source -> Sink Mode -> Enable and hit enter. Then exit back to the main screen. Alternatively, the remote command is:

smuX.source.sink = smuX.ENABLE

where the X above is A or B for the channel you are using. In your case, B. Now, if you wish to use it then in a source quadrant, you must then disable sink mode to ensure you have correct accuracy there. But yes, I would suggest both Sink Mode enabled and remote sense (4W) for your load SMU.

Luigi_B
Posts: 9
Joined: October 26th, 2011, 6:36 pm
Country: United States

Re: 2-wire and 4-wire Voltage measurements

Post by Luigi_B » November 2nd, 2011, 12:02 pm

Thank you very much for the useful information.

I set my Channel B to 4-wire (also added the sense leads to the back from ChB) and I set ChB to Sink Mode. The measurements are a lot better now.

I just have one more concern: Having Channel B in Sink mode, I want to control the sinking current, therefore I put my channel in Current source mode to control the current. I am suppose to see "SrcB_" in the Main Display but I don't see the bar in current source only in voltage source (which is reasonable because that is where I went to set the channel in Sink mode.) Is that Channel still in sink mode although I don't see the underscore bar under Current Source mode? Can someone clarify please.

Thank you.

Nathan S
Keithley Applications
Keithley Applications
Posts: 254
Joined: February 28th, 2011, 6:17 am
Country: United States
Contact:

Re: 2-wire and 4-wire Voltage measurements

Post by Nathan S » November 2nd, 2011, 12:59 pm

You should still be in sink mode. You can check this by if connected remotely, send:

print(smuX.source.sink)

This will return a 0 or 1 showing whether Sink Mode is Off or On respectively.

Post Reply

Return to “Low Voltage Measurements”

Who is online

Users browsing this forum: No registered users and 2 guests