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Re-calibrating bench PSU

Started by bitrex July 17, 2020
On Fri, 17 Jul 2020 23:11:22 -0400, bitrex <user@example.net> wrote:

>tweak it at the low >end, turn the voltage up to max and it'll read high there, tweak it down >a bit, turn it back down to the low end and adjust it again there, and >just kinda do the best you can
I can't read your schematic, but normally, there should be two pots for calibration. One for gain and one for offset. You adjust the offset at a low voltage, and then turn the voltage to high. If it reads high, you reduce the gain and then go back to low and readjust the offset. Keep going back and forth until you are happy. -- RoRo
On 7/18/2020 8:22 AM, Robert Roland wrote:
> On Fri, 17 Jul 2020 23:11:22 -0400, bitrex <user@example.net> wrote: > >> tweak it at the low >> end, turn the voltage up to max and it'll read high there, tweak it down >> a bit, turn it back down to the low end and adjust it again there, and >> just kinda do the best you can > > I can't read your schematic, but normally, there should be two pots > for calibration. One for gain and one for offset. > > You adjust the offset at a low voltage, and then turn the voltage to > high. If it reads high, you reduce the gain and then go back to low > and readjust the offset. Keep going back and forth until you are > happy. >
'Fraid there are only two adjustment pots on the sense amp board total, for both current and voltage signal input to the uP ADC. Looks like the output voltage and voltage across the current sense shunt are both fed to a LM358 gain/buffers and then the trimpots are the series component of a voltage divider hung off the output of the '358 buffers, prior to going into the ADC. The trimpot in the current sense line was bad. Replaced that and it's looking better, I can tweak it to adjust the current display value. Problem is now it won't go high enough, 10 volts across 50 ohms reads 100 mA and I can use the trimpot to push that up to 120 mA and down to 0, but not up to 200mA where it needs to be. There's a button on the PCB that zeros out the current display so now I guess I have to figure out where the trimpot and other controls need to be set so I can hopefully zero it appropriately and push that up to the correct value