USB 6210 analog input won't recognize load cell voltage data correctly

[denarol]

I have a USB 6210 DAQ Board and I am trying to input a continuous load cell voltage with respect to ground (RSE). However, when i connect the load cell to the board (+ output to AI pin, - output to AI ground) it shows a 2V peak to peak, high freq. waveform centered at 0V. This doesn't increase when a load is applied either. I have also tried other load cells, they all exhibit the same characteristics.

When i connect a variable power supply, the USB 6210 reads the voltage data fine. Additionally, i have measured the load cell output using a DMM and the output is acceptable, so the load cells are working and outputting the correct voltages.

Does anyone have any idea why the USB 6210 board will not read the voltage data correctly, when the DMM is? Why will a variable power supply input data correctly but the sensors exhibit a noisy, high freq waveform?

I am using LabVIEW 2009, DAQmx 8.9.5 and all tests have been run using the DAQmx test panels.

[Ali M]

Hello denarol,

Usually a bridge-based data acquisition device is recommended e.g. NI 9237 instead of an AI card, since the ratiometric sensor returns a mV/V value, which is the ratio of output voltage to input voltage, i.e. excitation. Additionally, these connections require at least 4 wires: Ex+, Ex-, AI+, AI-. For the AI card, see the following link on how to accomplish the set up for your application: Using a Bridge-Based Sensor with an Analog Input

Best regards,

Ali M

Applications Engineer

National Instruments

[denarol]

My load cell is connected the same way, the excitation voltage is just externally powered instead of from a board. I am just confused because the input is acting as a floating ground or like its ungrounded even though the sensor is connected to the AIGND pin.

Should i be using some additional components (shunt resistors) in the circuit?

Is this lack of additional components why my DMM reads the data fine, but the card wont?

[P.Sanders]

Have you tried connecting your signal to a differential pair of your DAQ card? The link says connect AI+/AI- of your signal to analog input channels. Use a differential pair instead of AI+ and AIGND. Differential pairs are usually A0 and AI8, AI1 and AI9 and so on. Ciao 🙂