cRIO NI9205 current shunt differential measurement

[B_Lind]

Trying to make differential measurement of the voltage drop of a low side current shunt to monitor battery current.

The battery is isolated from the cRIO NI9205 measurement common. Is it necessary to add a 100k resistor to common to ensure that my common mode is within spec's.

What measurement accuracy would you expect if a 0.2% shunt resistor was used ?

[JoshY]

Hi Brooks,

I believe you would need a bias resistor when taking dfferential measurements. Please refer to our Field Wiring Guide for a more detailed explanation as well as diagrams. Also, measurement accuracy is dependent on the input range. A table of this can be found in the 9205 user manual.

[Henrik_Volkers]

Some remarks to the accuracy:

Tempco of the shunt?  The current will heat up the resistor and the value will change ....

The absolute value of your shunt can measured by a calibration...

I hope you use 4 wire technique

If you are not only measuring a DC current the impedance of the shunt is important. ( inductivity and capacity ... yes even a shunt can have a resonant frequency 🙂 )

Usually the datasheet of the shunt will give you an answer.