On 4 dec, 20:55, Terry Reedy <tjre...@udel.edu> wrote:
> On 12/4/2012 7:14 AM, Jean Dubois wrote:
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> > The following test program which tries to communicate with a Keithley
> > 2200 programmable power supply using usbtmc in Python does not work as
> > expected. I have connected a 10 ohm resistor to its terminals and I
> > apply 0.025A, 0.050A, 0.075A en 0.1A,
> > I then measure the current and the voltage en write them in a file
> > De data produced looks like this:
> > 0.00544643 0.254061; first current value is wrong, voltage value is
> > correct
> > 0.0250807 0.509289; second current value is wrong, but it corresponds
> > to the first, second voltage is correct
> > 0.0501099 0.763945; 3rd current value is wrong, but it corresponds to
> > the second, 3rd voltage is right
> > 0.075099 1.01792; 4th current value is wrong, it corresponds to the
> > 3rd, 4th voltage is right
> > 4th correct current value is missing
>
> > But is should be (numerical inaccuracy taking into account) (these data
> > were produced by a similar octave-program):
> > 0.0248947 0.254047
> > 0.0499105 0.509258
> > 0.0749044 0.764001
> > 0.0998926 1.01828
>
> > Here is the python-program:
> > #!/usr/bin/python
> > import time
> > import os
> > import sys
> > measurementcurr=''
> > measurementvolt=''
> > timesleepdefault=1
> > filename ='mydata.txt'
> > usbkeith = open('/dev/usbtmc1','r+')
> > usbkeith.flush()
> > usbkeith.write("*IDN?\n")
> > #strip blank line:
> > identification=usbkeith.readline().strip()
> > print 'Found device: ',identification
> > usbkeith.write("SYST:REM" + "\n")
> > usbkeith.write(":SENS:VOLT:PROT 1.5\n")
> > keithdata = open(filename,'w')
> > #start first measurement
> > usbkeith.write(":SOUR:CURR 0.025\n")
> > usbkeith.write(":OUTP:STAT ON\n")
> > time.sleep(timesleepdefault)
> > usbkeith.write(":MEAS:CURR?\n")
> > time.sleep(timesleepdefault)
> > measurementcurr=usbkeith.readline()
> > print 'Measured current 1: ',measurementcurr
> > usbkeith.write("MEAS:VOLT?\n")
> > time.sleep(timesleepdefault)
> > measurementvolt=usbkeith.readline()
> > print 'Measured voltage 1: ',measurementvolt
> > keithdata.write(measurementcurr.strip()+' '+measurementvolt)
>
> [3 near repetitions snipped]
>
> This sort of repetitious code without even line breaks is painful for me
> to read. Python has looping statements for a reason. Replace all four
> nearly identical blocks with the following. (If you are not familiar
> with built-in enumerate, you should be. Read its entry in the library
> manual.)
>
> for number, current_in in enumerate(
> ('0.025', '0.050'. '0.075', '0.100'), 1)
> usbkeith.write(":SOUR:CURR %s\n" % current_in)
> ...
> print 'Measured current %d: ' % number, measurementcurr
> ...
> print 'Measured voltage %d: ' % number, measurementvolt
>
> Now you can make changes in only one place and easily add more test values.
>
> > print "Goodbye, data logged in file:"
> > print filename
> > usbkeith.close()
> > keithdata.close()
>
> > can anyone here what is going wrong and how to get it right?
>
> No, but if both the python and octave programs used loops, it would be
> easier to see if both are doing the same things before, within, and
> after the loop.
>
> --
> Terry Jan Reedy
I followed your suggestion an now the code looks like this:
#!/usr/bin/python
import time
import os
import sys
measurementcurr=''
measurementvolt=''
timesleepdefault=2
filename ='mydata.txt'
usbkeith = open('/dev/usbtmc1','r+')
usbkeith.flush()
usbkeith.write("*IDN?\n")
#strip blank line:
identification=usbkeith.readline().strip()
print 'Found device: ',identification
usbkeith.write("SYST:REM" + "\n")
usbkeith.write(":SENS:VOLT:PROT 1.5\n")
keithdata = open(filename,'w')
usbkeith.write(":OUTP:STAT ON\n")
for number, current_in in enumerate(('0.025', '0.050', '0.075',
'0.100'), 1):
usbkeith.write(":SOUR:CURR %s\n" % current_in)
time.sleep(timesleepdefault)
usbkeith.write(":MEAS:CURR?\n")
measurementcurr=usbkeith.readline()
print 'Measured current %d: ' % number, measurementcurr
usbkeith.write(":MEAS:VOLT?\n")
measurementvolt=usbkeith.readline()
print 'Measured voltage %d: ' % number, measurementvolt
keithdata.write(measurementcurr.strip()+' '+measurementvolt)
usbkeith.write(":OUTP:STAT OFF\n")
print "Goodbye, data logged in file:"
print filename
usbkeith.close()
keithdata.close()
Still there is a "buffer-problem" as you can see in the output below:
0.00639725 0.0104065; these values are completely wrong
0.0248976 0.262959; these should have been be the first values
0.0500431 0.516602: these should been the second values
0.0749168 0.772616; these are the 3rd values
4th values are missing
any idea why this does what it does in Python?
jean
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