MCC 128 odd behaviour?

[NicR]

I have an MCC 128 attached to an AT 50 B10 split core current transformer. I'm running the logging demo & getting some odd results.

I have a mains cable (UK) running through the CT which sould be reading 0 as both the live & the nutral are threaded through but I'm getting a ±7 VAC signal instead!

Sketch of set up,

 

The CT should be giving a voltage between 0-10V depending n the current through the threaded cable (& in this case it should be 0 as the nutral is included) but instead I get..

 

Any idea whats going on here?

Edited May 26, 2023 by NicR
typos

[Fausto]

Hello @NicR.

What does the MCC 128 measure when the cable is removed from the CT?  If it reads 0 Vots, then disconnect the CT from the MCC 128 and connect it to an oscilloscope.  What does the oscilloscope show with and without the cable?

Regards,

Fausto

[NicR]

Found the problem as soon as I posted, the DAQ channel & the CT need the same ground reference. Connected both -ve terminals to pin 39 on the Pi GPIO & its all working fine.

[Fausto]

Thanks for the update.