Measuring several 4-20 mA loops with single ended AI channels.

[jandro]

Because of budget and space constraints I wish to measure five 4-20 mA current loops using the single ended AI inputs of the NI-9381. This card will also allow me to control some DC motors via the AO channels and monitor e-stop state using the DIO inputs. I also need two 16ch TC modules and one 32ch DIO modules filling up the cDAQ-9184 four-module chassis.

My question: Can I use the single ended AI and external shunt resistors for current measurements? Something like:

[johnsold]

You should be able to do that PROVIDED that all the current loop devices are powered from the same voltage source as shown in your drawing.

Be careful about the grounding of all the devices in your system so that you do not get ground loops carrying motor current!

Lynn

[Izzzzz]

Hey Jandro, 

Please note that the 9381 is not supported in a cDAQ-9184. You will need a cRIO chassis to use this module. 

Regards, 

Izzy

[jandro]

Thank you. I did not think about the motor currents, however I only connect to a control board that is optically isolated from the motors.

AA

[jandro]

Izzy,

Well, that's a bummer. I was trying not to get into the cRIO platfom yet. Looks like I either take the pluge or look into a bigger cDAQ chassis to solve the problem. 

Jandro