Hello,
I am working on a PCB with relays that require a 24VDC coil voltage and op-amps that require +-12VDC supply voltage. I am using two AC/DC power supplies from Automation Direct (PSB24-060S-P (24V) and PSE12-215 (+-12V)). My original thought was to connect the negative terminal of the 24V supply and the COM terminal of the +-12V supply to the common ground plane located on my board (which is also attached to a DAQ ground). The problem is that I am unable to connect the 24V ground and +-12V COM because there is potential, measured via DMM, between these two points. If I attempt to connect the +-12V COM terminal to the 24V negative terminal the LED on the +-12V quickly goes out...I assume that I am creating a short and the +-12V is powering down.
Additionally, it appears that the +-12V supply is not sharing any common voltage with respect to the 24V supply. With respect to 24V supply negative terminal, the +-12V supply positive rail is 21.0V above, the COM terminal is 9.0V above and the negative terminal is -3.0V above (3V below).
Originally, I would have guessed that the 24V negative terminal and +-12V COM terminal would have shared a common point (guess not since the outputs are each isolated from input
) and +12V, -12V (wr to 24V negative terminal) for the other +12V terminals.
Edit: A requirement of the PCB is that the 24V supply be separate from the +-12V supply since it will be powering the PCB relays and may cause some switching noise which may cause noise if connected to +-12V power suppy (op-amp power supply terminals). If I do not intend to do any relay switching while measuring the output of the op-amps with my DAQ do the power supplies necessarily need to be isolated? If they are isolated can I ever refctify the grounding issue?
Has anyone ran into this issue before and found a good solution to 'force' the 24V negative terminal and +-12V COM to same potential or can recommend a system/power supply combination that would resolve the grounding issue?
Thank you so much in advance and I look forward to learning from you all.
Cheers,
L