Unusual circuit with retro-feel (specialist PCB cleaning machine)

Описание: Vic got in touch about an unusual PCB that is used to provide operator feedback on roller pressure in a PCB cleaning machine. It seems quite an old design with hand-made PCBs for the specialist application.

The manufacturer does have a setup guide for tuning the meter, but it's one of those "We know how it works, but it's hard to describe." things.
My guess is that the front panel calibration pot would be set to a mid position, then the machine would be run for a while with the rollers lifted up and running free to allow the machine to stabilise on a no-load current. The calibration pot on the PCB would then be tweaked so the needle points at "2" on the dial (it's just a number - it doesn't relate to actual current).

I don't recommend turning both calibration pots to their extremes as it may result in high meter current.

With modern cheap LED current meters it might be viable to replace the meter with a standard digital display and then get used to the typical numbers for optimum roller pressure. I'd tend to write the sweet-spot pressure current next to the display. Ultimately, a seasoned operator has a feel for the machine, so they'd tend to just click with the numbers as a handy load reference indicator.


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