I am trying to measure the output voltage from the pressure sensor and scale it to units of mmHg and read in the result in NI MAX. The sensor outputs 0.2584 mV/psi/Volt excitation, so if my math is correct, using a 5V excitation means 1.292 mV/psi. I want the result in units of mmHg, meaning an output of 0.024983 mV/mmHg. I am working in physiological ranges (<150 mmHg) and this is a very small output, is it even possible to get an accurate reading with the NI 9205's +/- 200mV range?
In NI MAX, I have created a task that provides 5V excitation to the sensor from the NI 9263. A different task records the input from the NI 9205, but even with custom scaling I am unable to get an accurate reading.
What is your Signal Input Range set to when using Volts as your Scaled Unit?
I ask because if the range is too large, you won't be using the full range of the ADC in your DAQ device and your results will not be as accurate. You can find more information on this in the link below
How to Increase Precision on Analog Input DAQ Device
As long as the absolute accuracy of the device under the current operating conditions is sufficient for the resolution of the sensor, the information in the above article should hold. For information on how to calculate the absolute accuracy, refer to the datasheet (linked below).
NI 9205 Datasheet
Thanks for the reply. I'm now trying without the pressure sensor just to see if I can just get an accurate reading with the NI 9205. Using the +/- 200 mV range, I am trying to acquire a 100 mV DC signal from the NI 9263. This is what I get using the above parameters from the 9205:
What could be causing so much fluctuation? From the datasheet, the absolute accuracy at that range is 175 μV but there seems to be aabout ~50 mV offset.