myRIO - Measuring single ended output using differential input

[PrasanthTP]

Hi all,

I had been using myRIO 1900 to measure output from microphone that ranges from 0 to 5V (biased at 2.5V).

I was using one of the single ended Analog Input ports in MXP connector A or B to read the value.

Due to some reasons, i changed the microphone with an amplifier and when measured using oscilloscope and other DAQ devices, the output range from +5V to - 5V.

As the MXP can't read -ve voltage, i realised that I need to change the connection to MSP Connector C.

It's mentioned in the myRIO dataheet that we can measure differential analog input channles upto +/- 10 V.

Though there are some reference materials available, i don't completely understand how to read single ended output using differential input.

Should I use any op-amp's or just directly wire them?

Can anyone kindly explain me the differences and some reference on how to connect them!

Though i tried to read through this white paper, i felt completely lost 😞

https://www.ni.com/en/shop/data-acquisition/measurement-fundamentals/field-wiring-and-noise-consider...

Single ended output from micorphone and/or amplifier has 2 pins: Vout and GND

Different input has 3 pins: A+, A- and AGND

I had attached the screenshot of the OPAMP data sheet for your reference

[Sam_Sharp · Accepted solution]

I believe you just need to connect your Vout to the +ve differential termination, the GND to the -ve terminal. (Briefly) A single-ended measurement is between the AI channel and AGND whereas a differential measurement is between the +ve and -ve terminal. A single ended measuring device is referenced to GND so that's where you're measuring the voltage from.

[PrasanthTP]

Thanks Sam_Sharp 

Though i made the connection as if what you had mentioned in the post, the values read were very strange.

After seeing your post, i went back to my check my connections and verified my program to realise that i was using U16 data type FIFO to transfer the analog data from FPGA to myRIO. Once I changed it to I16, the program was working seamlessy.