Brymen BM869s DC min crest

[oxoocoffee]

Hello,

I got my new 968s unit and last Friday to wanted to take measurement on my Nvidia Nano 40 pin 5V to ground.

Setup:
So I have camera that is about 65Feet away from my Nano. This camera is connected using usb-over-ehternet. So I need to provide 5V external power to module on opposite side or nano to provide external power. So along the the Ethernet cable I have 18awg cable connected to 40 pin on nano to supply 5V. I am considering also switching to 12 V and use buck converter at the other end to connect to 5 V. Please note this is temporary solution since I am considering CAN FD or PoE for remote thermal camera.

Issue:
Then I connect my 869S to measure voltage on 5V pin to ground I select DC and crest min to log minimum voltage over time. The issue I am seeking that such voltage drops to around 5.06V (where no load placed on such 5V pins, voltage is around 5.2V). After several hours ~15 or more I see -4.65V on my multimeter. Not sure how to explain this. Is this some problem with multimeter running for a long time? Does any one noticed this?
Or is there some other explanation.

Thank you for all comments

[radiolistener]

it's just random interference on wires which you're using to attach DMM to the circuit.

BM869/BM867 has wide bandwidth in CREST mode. Just tested, it's 3 dB bandwidth is about 1055 Hz. So it very sensitive to a noise and pulse interference. Your wires just works like antenna and receiving electromagnetic pulses from other equipment in your environment. This affects the measurements results. Also it may be just a noise of DMM ADC.

When you use usual DC measurement mode, the DMM filters all these pulses and show you average value. But when you use CREST mode, you will see all noises.

[oxoocoffee]

Thank you for your help and explanation.
I think a better option for what I wanted to accomplish is pressed REC mode in DC and check Min/Max to read RMS peaks.

I did read multimeter documentation and I am a bit puzzled when you use Crest min/max vs Rec min/max?

Could some one explain each case and when to use each?

On another hand, what I did experienced  in Crest mode is still strange to me that polarity was almost reversed just by induction? That much? I like to lear more about that.