MC USB-202 Input Voltage wavers at ~0.25 V

[DLewis]

I am working with a USB-202. It is attached to a flow meter which outputs a 0-5V flow rate signal that is being read in LabView in order to plot flow rate over time. For the most part everything works as expected, however when the DAC receives a steady input voltage of ~0.25 volts from the flow meter, the LabView program reads it as varying from ~0.2-0.3 V. The voltage at the DAC input pins is a steady ~0.24-0.26V when measured with a multimeter. This range of voltage is consistent with the expected precision of the flow meter. I am using ULx sub VI's to create and read channels from the DAC. Let me know if I can provide more detail. 

[DAQman]

The measurement should be closer to 0.25 because the worst-case noise performance is +/-24mV. My USB-202 returns 0.2516 when I apply 0.2500 volts using a voltage calibrator—some things to remember. Measuring the sensor using a voltmeter is not the same. This is because the voltmeter uses a different type of A/D converter that performs much averaging. Also, when you say the reading is between 0.2 and 0.3, it implies one decimal place. If this is how you display the data, you're getting rounding errors. And last, if you have signals connected to the other channels, they could influence the measurement depending on what they are. 

 

 

[DLewis]

Thank you for your response! To clarify, my LabView program is reading the input voltage with 3 decimal places of accuracy, but the signal deviates by ~5%. The multimeter's measured signal is more in line with the expected precision of the flow meter (+/- 1%) which makes me think there is an issue with my program.  I tried disconnecting other inputs and outputs with no success. I am using two AI's two AO's and 2 DIO's (as outputs).