Hi folks,
Just wondering if im being an idiot with my DMM. I was gifted a HP 3457A by my mentor when he retired. Its not been calibrated since about 2006.
I have been repairing a WEIR 4000T Linear PSU, and i had the DMM connected to its output terminals, while also having my Scope connected measuring output Ripple.
While the DMM was connected, i was detecting some odd switching noise on the PSU output on the scope, I thought it may have been noise coupled on the DMM leads as its a HiZ input, however disconnecting the DMM leads at the DMM (still connected at the PSU end) the switching noise disappeared. This leads me to believe its coupled in by the DMM.
Surely a DMM of this quality shouldnt be passing switching noise onto its measurement terminals? Am i missing something?