analog signal change(module 9381) in labview when activating switch on relay module (NI9481) on seperate circuit

[hlp105]

We are getting analog voltage changes in Labview on several different inputs (not found with multimeter). It happens when we activate the NI 9481 relay module with a 24V DC signal to power a solenoid. Don't understand why this is happens or why it shows on three different inputs in LabVIEW but not when testing the points with a meter.

[Dennis_Knutson]

This has nothing to do with NI's signal conditioning hardware.

I don't understand what you are saying. The 24 volts is being measured? Something else? With what besides the meter? LabVIEW is software so it can only report what some hardware is measuring.

[Henrik_Volkers]

Some more information is needed!

How does your setup looks like? Cabling?

How do you measure your voltage?    (Can you capture some voltages in high sampling mode while switching?)

I assume an EMC issue.... however my crystal ball unforseeable drops from my desk 😄

[hlp105]

The 24V is only sent from power supply through relay to solenoid. The inputs are all 4-20 mA signals converted to 1-5V by a 250 ohm resistor across the ckt. The inputs come from a LVDT, extensometer, and a load cell. We had to convert the signals to make them readable by the 9381 module that we already had.

[Henrik_Volkers]

That picture is of little help, since the devices will report what they measure, wether it is the voltage of interest or not 😉

To find the root cause of that effect, you 'just' have to follow the current. However current and to note _fast changing current_  can go funny, not always so obvious ways.

That's why I asked for details of the setup, and every wire counts 😉

(and ground is a con......   see sig)

And a as fast as possible sampled voltage channel while a switch is actvated (say 20ms) would help too.