USB-6211: Analog Input (Differential Measurements)

[azri.azizan]

Greetings,

I used the USB-6211 Analog Input pin to measure the voltage of the laser. The setup is the same as attached picture. Basically, the light will project into the amplified detector (PDA100A2) and direct to the dedicated power supply. Then, the output is connected to the Analog Input pin of the USB-6211. 

The main question is when I run the test panel or task inside the NI MAX in differential mode, why is the measurements or value keep increasing until one point/value around 10.9 V and then it become constant graph and stay at the 10.9 V value? The correct way of doing this measurements is by using the RSE mode since I just only use single ended input not the differential (Already tested and obtained correct result). I just want to know, what makes the voltage kept increase until one point and it stay at that point forever. 

Thank you in advance.

[santo_13]

Please share the connections made when you used Differential mode, I guess you've made incorrect connections and hence the measurement was drifting and saturated.

[TakeANap]

This kind of behaviour is similar what happens when amplifiers missing bias-resistors. Google "bias resistors".