We investigated temperature monitor circuit for the high power beam dump of PRM reflection.
We found two things about 18V power cable that was connecting the rack and the circuit.
(1) If you are not careful when inserting the 18V power cable (hereinafter referred to as the cable), the pins inside the cable plug may be bent.
(2) There was a potential difference of 18V between the ground pin of the cable and the chassis of the cable plug when the cable was connected to the rack.
Regarding (1), I think it is a problem that users must pay attention to. I attach an enlarged photograph of the plug of the cable that is actually connected to the temperature monitoring circuit. You can see that the metal plate that composes the ground pin of the plug is bent outward (photo, red circle).
When I tried to use the circuit in this state, +18V was not supplied to the power supply.
By fixing the pins and inserting the plug of the cable and the socket on the circuit side so that it is not slanted, the pins can be inserted without bending, and power can be supplied to the circuit. "Be careful not to be slanted and fit" is important.
(2) is a mysterious problem. I solved the problem of (1) and the circuit started to move, but when I tried to put this circuit box on the floor, sparks scattered. Then, when measuring the potential difference between the box of the circuit box and the SUS plate on the floor, it was 18V.
This was strange, so I looked into the circuit and found no problems. Next, I measured the potential between the chassis of the plug of the cable and the ground pin of the plug with the circuit and the cable disconnected, and it was 18V. I think that the potential difference should be 0, so I found it strange.
Next, I removed the cable from the rack and checked the continuity between the chassis and ground in the stand-alone state, and found that insulation was achieved.
I brought another cable for trial, connected it to the rack, and measured the potential difference between the chassis of the plug and the ground pin of the plug. Even though it was not 0, (I think it was about 100 mV). It was much smaller than 18V. When this cable was connected to the circuit box, the circuit worked, and even on the floor, there was no spark like before.
This is the reason of problem (2).