How to read low level voltage by multifunction DAQ

[Ahedayat]

I want to wire my milivolt pressure transducer to analoge input of NI PXI-6143. The transducer has 4 wires, two for excitation and two for the output signal. I have excited the transducer with the power supply and used the volt meter to read the output. It worked fine. Right now, I want to sample the voltage by using the NI-PXI 6143 card. I connected the +/- signal output of the transducer to one of eight channels of the card and observed that the measured signal is mostly noise and It is almost impossible to get the same voltage as the voltmeter shows. I think sth is wrong in wiring the transducer. I have directly connected the power supply to the DAQ input using the resistor on the - signal channel connected to the ground and it worked fine. I think the wiring is working for high range of voltage. I have also connected the +/- signals of the transducer by a capacitor and then connected them  to the analoge input. It gave me more stable reading but still different than the actual value which is read by voltmeter. I am wondering if anybody can help me to find out how to read the low level voltage input.

regards,

Ahmad

[HeatherBaker]

Hi Ahmad,

The NI-6143 is a 16 bit data acquisition device with a signal input range of +/- 5V.  Absolute accuracy for the card is specified at 3.613mV which is why you are having issues reading correct measurements at lower values.  A data acquisition device with either a lower input range would provide you a significantly better reading.  A card with multiple input ranges can be more flexible in the long term.  There are also data acquisition cards specifically designed for bridge based sensors and may alleviate the need for external excitation.  I recommend contacting a technical sales representative at 888-280-7645 to discuss all of your needs and determine the best option.