LabjackPython giving unstable analog input readings

Hi all,

I am using a labjack EU9 to read two analog voltages. One is the voltage directly output from a 3.3v regulator (henceforth reference), the other is the voltage from an NTC thermistor voltage divider (via a unity gain OPAMP buffer) - henceforth called signal.

I have a python script using the eu9 library from the UD Driver which just reads the ADC for each analog input, converts it to a voltage and prints it to console every time I press the any key. I also have some test code that is reading the voltage using getAIN().

The problem that I am having is that the signal voltage that I read is extremely noisy. The reference voltage however is very stable and accurate. I believe the problem lies in my python code as when I open LJControlPanel, the signal voltage shown is spot on what my (calibrated) multimeter reads. I have tried physically switching the analog inputs, however the reference voltage is always good and the signal voltage is always bad regardless of which analog input I use.

LJControlPanel Test Screen: (signal voltage matches multimeter to the mV)

http://imgur.com/a/FGINI

The Circuit:

Four connection go to the Labjack, Vcc and ground go to the labjack VS and GND pins. Sig goes to AIN3 and Vref goes to AIN2

https://i.imgur.com/OwbSuiq.jpg

My Code:

import ue9
import sys
import time


def main():

# Create an instance of the labjack
try:
lj_UE9 = ue9.UE9()
except:
print "Failed to find or connect to the labjack."
safe_exit()

print "Connected to labjack device: \n{}".format(lj_UE9.getCalibrationData())

AIN_reference = 3
AIN_thermistor_divider = 2

while True:
batman_is_a_jerk = raw_input("Press any key to take a reading, 'q' to exit.\n")
if batman_is_a_jerk == 'q': break
rawSig = lj_UE9.singleIO(4, AIN_thermistor_divider, BipGain=0x00, Resolution=12, SettlingTime=100000)
time.sleep(0.1)
temp_vSig = lj_UE9.getAIN(AIN_thermistor_divider)
time.sleep(0.1)
rawRef = lj_UE9.singleIO(4, AIN_reference, BipGain=0x00, Resolution=12, SettlingTime=100000)
vRef = lj_UE9.binaryToCalibratedAnalogVoltage(rawRef["AIN%s" % AIN_reference], 0x00, 12)
vSig = lj_UE9.binaryToCalibratedAnalogVoltage(rawSig["AIN%s" % AIN_thermistor_divider], 0x00, 12)

print "ref: {} ({} V)\tsig {} ({} V) -- ({}V)".format(rawRef["AIN%s"%AIN_reference], vRef, rawSig["AIN%s"%AIN_thermistor_divider], vSig, temp_vSig)


lj_UE9.close()




def safe_exit():
print "Exiting..."
sys.exit()

# Entry point when this function is called directly
if __name__ == '__main__':
main()

And output from that code: (note sig should read 1.06V)

Connected to labjack device: 

{'ProAINOffsets': {'0': None, '8': None}, 'DACSlopes': {'1': 837.614071714459, '0': 837.9161202218384}, 'AINSlopes': {'1': 3.9082253351807594e-05, '0': 7.818220183253288e-05, '3': 9.747687727212906e-06, '2': 1.951633021235466e-05, '8': 0.0001576784998178482}, 'TempSlope': 0.012650741264224052, 'ProAINSlopes': {'0': None, '8': None}, 'AINOffsets': {'1': -0.01301439804956317, '0': -0.01243095682002604, '3': -0.013334714574739337, '2': -0.013114978792145848, '8': -5.213795782998204}, 'DACOffsets': {'1': -22.210517883533612, '0': 2.330915938830003}}

Press any key to take a reading, 'q' to exit.

ref: 42400.0 (3.30249440088 V) sig 15120.0 (1.16968393489 V) -- (0.952024684986V)

Press any key to take a reading, 'q' to exit.

ref: 42400.0 (3.30249440088 V) sig 12336.0 (0.952024684986 V) -- (1.0420905815V)

Press any key to take a reading, 'q' to exit.

ref: 42400.0 (3.30249440088 V) sig 12320.0 (0.950773769757 V) -- (1.34981572791V)

Press any key to take a reading, 'q' to exit.

ref: 42416.0 (3.30374531611 V) sig 18720.0 (1.45113986148 V) -- (0.949522854527V)

Press any key to take a reading, 'q' to exit.

ref: 42400.0 (3.30249440088 V) sig 13360.0 (1.03208325966 V) -- (0.950773769757V)

Press any key to take a reading, 'q' to exit.

ref: 42400.0 (3.30249440088 V) sig 19056.0 (1.4774090813 V) -- (1.39985233708V)

Press any key to take a reading, 'q' to exit.

ref: 42400.0 (3.30249440088 V) sig 12256.0 (0.945770108839 V) -- (0.945770108839V)

Press any key to take a reading, 'q' to exit.

ref: 42400.0 (3.30249440088 V) sig 12288.0 (0.948271939298 V) -- (0.948271939298V)

Press any key to take a reading, 'q' to exit.

ref: 42400.0 (3.30249440088 V) sig 12624.0 (0.974541159114 V) -- (0.948271939298V)

Press any key to take a reading, 'q' to exit.

q

Process finished with exit code 0