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Problem with voltage measurement using keithley 2000

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willyc
Posts: 4
Joined: December 12th, 2013, 3:10 pm
Country: United States

Problem with voltage measurement using keithley 2000

Post by willyc » January 27th, 2014, 12:55 pm

Hello,

First of all, I'm testing load regulation using keithley 2000 meter to measure input voltage and keithley 2420 sourcemeter for load current. My load setup is from 0A to 3A, 0.5A steps and Vin is 12V. Please see code below. My problem was, when I measure input voltage at 0A load, I'm measuring 12V which is fine but when the program increments the load to 500mA, I'm was measuring 11.2V for input voltage. And then after that, the rest of the load steps, I'm measuring 12V for input voltage, which were fine. I got stuck with this problem. I appreciate any help. Thanks in advance.

Willy

def config_keithley_isrc(): # configure setup for the keithley 2420
keithley_isrc.write("SOUR:FUNC CURR")
time.sleep(delay1)
keithley_isrc.write("SENS:VOLT:PROT 21")
time.sleep(delay1)
keithley.isrc.write("OUTP:SMOD HIMP")
time.sleep(delay1)
keithley_isrc.write("FORM:ELEM CURR")
time.sleep(delay1)
keithley_isrc.write("OUTP ON")
time.sleep(delay1)
return

def config_keithley_vin():
keithley_vin_dmm.write("CONF:VOLT:DC")
time.sleep(delay1)
keithley_vin_dmm.write("FORM:ELEM READ")
time.sleep(delay1)
return

def measure_vin(): # configure to measure the input voltage
keithley_vin_dmm.write("READ?")
time.sleep(delay1)
input_voltage = keithley_vin_dmm.read_values()
time.sleep(delay1)
vin.append(input_voltage)
time.sleep(delay1)
return

def measure_iout(): # configure to measure current from the keithley 2420
keithley_isrc.write("MEAS:CURR:DC?")
time.sleep(delay1)
iout_keithley_load.append(keithley_isrc.read_values())
time.sleep(delay1)
return

Dale C
Keithley Applications
Keithley Applications
Posts: 2841
Joined: June 10th, 2010, 6:22 am
Country: United States
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Re: Problem with voltage measurement using keithley 2000

Post by Dale C » January 29th, 2014, 10:59 am

So the trouble is only at 500mA output current?
What is the voltage compliance set to? The code you provided shows it is at 21V which should be fine.
But what is the voltage measurement range set to? I would suggest it be set to 21V range.
Maybe you are in "range" compliance.
Can you perform this sequence on the front panel and not use software to see if the 500mA still gives the 11.2V on the Model 2000?
Maybe that will give us a clue.

willyc
Posts: 4
Joined: December 12th, 2013, 3:10 pm
Country: United States

Re: Problem with voltage measurement using keithley 2000

Post by willyc » January 30th, 2014, 9:43 am

Hi Dale,

It was fine when I use the front panel (tested manually). Just to let you know that I'm testing a Buck Regulator circuit with the keithley 2420 connected to the output as load and I'm sinking current. So, in my program, I'm converting the current to a negative value. I think you're right, it's a software problem. Maybe there's a setup or command missing in my program. Thank you for helping me on this one. I appreciate it.

Willy

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