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switching from current to potential control

Models 2400, 2401, 2410, 2420, 2425, 2430, 2440, 6430
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DS1000
Posts: 7
Joined: August 22nd, 2011, 3:59 am
Country: Canada

switching from current to potential control

Post by DS1000 » August 22nd, 2011, 4:02 am

Hello,

I have a keithley 2400 source-measure unit that I control through GPIB using VB.net with a National Instruments GPIB card. I have no problems communicating with the device. I supply 0.2 A to a 0.5 Ohm resistor; V=0.1 V using the following command sequence, where K2400 is my device reference from the NI dll:

With K2400
.Write("ABORT;*CLS")
.Write("SOUR:FUNC CURR")
.Write("SOUR:CURR:MODE FIXED")
.Write("SOUR:CURR:RANGE:AUTO ON")
.Write("SENS:VOLT:PROT 4.5")
.Write("SOUR:CURR:LEV 0.2")
.Write("OUTP ON")
End With

This works fine. I then want to switch to constant potential mode and hold at 0.1V (current would be 0.5A). I send this command sequence:

With K2400
.Write("OUTP OFF")
.Write("ABORT;*CLS")
.Write("SOUR:FUNC VOLT")
.Write("SOUR:VOLT:MODE FIXED")
.Write("SOUR:VOLT:RANGE:AUTO ON")
.Write("SENS:CURR:PROT 1")
.Write("SOUR:VOLT:LEV 0.2")
.Write("OUTP ON")
End With

The device goes into compliance. If I press local on the front panel for the 2400, the SMU goes out of compliance and delivers the current needed. If I then resend the command sequence (putting the SMU back in to remote mode), voltage and current control performs as it should. To me it seems as though I need one more command to get this to work properly – possibly a command that is “sent” when switching to local mode? Any suggestions would be greatly appreciated
thank you

Nathan S
Keithley Applications
Keithley Applications
Posts: 254
Joined: February 28th, 2011, 6:17 am
Country: United States
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Re: switching from current to potential control

Post by Nathan S » August 22nd, 2011, 5:33 am

You're going into what we call range compliance on the 2400. This can be seen because if you look at the front panel, the units (A in this case) is blinking, not the Cmpl. The issue with the code is though your compliance value is set to 1A which would be above the source compliance level, your measurement range is still at the 100uA default. The way the 2400 is set up internally, you go into range compliance if you attempt to source more current than the maximum for your measurement range. Add in "SENS:CURR:RANG 1" after you set the 1A compliance level and before where you set the source voltage level to 0.2V. This should fix your issue by setting the measurement range to the 1A range.

DS1000
Posts: 7
Joined: August 22nd, 2011, 3:59 am
Country: Canada

Re: switching from current to potential control

Post by DS1000 » August 22nd, 2011, 6:04 am

Thank you Nathan, that worked perfectly!

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