Nandini Peisl

My full code is below for clarity. When sending TRAC:DATA? to the 2182A I get the number of elements back I set as TRAC:POIN. But only the first values are different and after that the last different value repeats until the number of points is reached. I am wondering why it is doing this.
Furthermore with my configuration of 0.1 PLC (and 50 Hz) -> minimum 2ms between measurements, 200 measurements, waiting 1 sec before reading the buffer, I am expecting 50 measurements but get 80. 
With PLC at 0.01, 200 measurements, 1 sec before reading the buffer, I get 20 measurements (and repetitions after that), although I am expecting more than with 0.1 PLC.
The measurement seems to be rather slow and the correlation between configuration and retrned measurements is strange. 

Could someone please help me with making my code faster and more reliable? It might be better to only read the buffer when it is full but I haven't found the commands for that. So please help me with that as well.

Thank you very much in advance.


# import libraries
from subprocess import Popen
import time
import numpy as np
import matplotlib.pyplot as plt
from datetime import datetime
import pyvisa
from collections import Counter

# set parameters:
resistance = 48 #Ohm
max_current_ampl = float(5e-3)

min_range = resistance*max_current_ampl
act_range = min_range + min_range*0.05

# initialize the resource manager
rm = pyvisa.ResourceManager()

def nanovoltmeter_com():
    try:
        time.sleep(6)
        nanovolt_start_time = time.time_ns()
        k218 = rm.open_resource('GPIB0::7::INSTR')   # k218 = Keithley 2182A = 'GPIB0::7::INSTR'
        k218.read_termination = '\n'
        k218.write_termination = '\n'
        k218.timeout = 20000    # 7 sec
        print(f"Instrument name: {k218.query('*IDN?')}")    # prints instrument name
        # set range
        nanovolt_opened = time.time_ns()
        k218.write('SENSe:VOLTage:CHANnel1:RANGe:AUTO OFF')
        k218.write(f'SENSe:VOLTage:CHANnel1:RANGe:UPPer {act_range}')
        # set plc
        k218.write('SENSe:VOLTage:NPLCycles 0.1') #can be 0.01 to 50

        time.sleep(2)

        k218.write('TRAC:POIN 200')
        k218.write('TRAC:FEED SENS')
        k218.write('TRAC:FEED:CONT NEXT')
        time.sleep(1)
        data = k218.query('TRAC:DATA?')
        print(data)
     

    except pyvisa.errors.VisaIOError as e:
        print(f"An error occured: {e}")


if __name__ == "__main__":
    nanovoltmeter_com()