Hi....I have a broken AF-test unit with an analog 100 miroAmp meter. And th at meter is broken. I have a 200 microAmp-meter that can suit my needs. I j ust replace the scale from the broken meter to the 200 micro-meter. But if I feed the instrument with a signal that should make 100% FSD, it just make 50% (of course)of FSD. Is ther someone that know about a circuit that can gain those 100 microamp to 200 microamp, in a linear way.
Would be very greateful Bo-Lennart Karlsson Falun, SWEDEN
meter is broken. I have a 200 microAmp-meter that can suit my needs. I just replace the scale from the broken meter to the 200 micro-meter. But if I feed the instrument with a signal that should make 100% FSD, it just make 50% (of course)of FSD.
200 microamp, in a linear way.Should be able to do that with an op-amp.
Would be very greateful Bo-Lennart Karlsson Falun, SWEDEN
++++++Isn't it always that way around. Is there a dropper somewhere that you could , as suck it and see initially, put a preset over to adjust . Unlikely as they would have used a 200uA movement originally but you never know, the calibration R may have enough play with any luck.
In a sense I'm looking forward to the day that I try to rewind an unobtanium meter movement for something worth repairing, like a valve tester. I've previously swapped a phosphor-bronze hairspring which is a daunting part of such a job
meter is broken. I have a 200 microAmp-meter that can suit my needs. I just replace the scale from the broken meter to the 200 micro-meter. But if I feed the instrument with a signal that should make 100% FSD, it just make 50% (of course)of FSD.
200 microamp, in a linear way.You will need to get the schematic for that area of the meter circuit so that a resistor can be recalculated for it.
It's more than likely the original meter was shunted with an R to do both a current scale and act as a damper for the needle movement.
The driving circuit most likely has more than enough to accommodate that 200ua meter after recalculations.
Jamie
A link to at least a partial schematic would be a big help. I need a meter for my HP 331 distortion analyzer, but all I can find are untested, used movements at five times what I paid for the analyzer so I am looking at building a digital display with a log converter.
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