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Gain 100 microAmp into 200 microAmp

B

Bo-Lennart

Jan 1, 1970
0
Hi....I have a broken AF-test unit with an analog 100 miroAmp meter. And that 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 make50% (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
 
J

JW

Jan 1, 1970
0
Hi....I have a broken AF-test unit with an analog 100 miroAmp meter. And that 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.
Is ther someone that know about a circuit that can gain those 100 microamp to 200 microamp, in a linear way.

Should be able to do that with an op-amp.
http://en.wikipedia.org/wiki/Operational_amplifier
See the third circuit down and read the description.
 
N

N_Cook

Jan 1, 1970
0
Hi....I have a broken AF-test unit with an analog 100 miroAmp meter. And
that 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.
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

++++++

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
 
J

Jamie

Jan 1, 1970
0
Bo-Lennart said:
Hi....I have a broken AF-test unit with an analog 100 miroAmp meter. And that 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.
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

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
 
J

Jamie

Jan 1, 1970
0
Arfa said:
It would actually be helpful if the OP told us just what this meter is
*actually* measuring. Is the unit some kind of AF generator, and the
meter is measuring the output level ? Or is it an AF measuring device,
reading peak or RMS values from some external place ? The meter will
only have a shunt resistor if it is actually being used to measure
current, and I'm struggling a bit to think of an 'AF Test unit' function
that involves measuring current rather than voltage.



On that score, I would agree

Arfa

All general analog coiled meters are calculated via current and a
voltage together regardless of their use. Even the iron vane meters
are treated this way. Etc.

For exact calculations you need to know the coil R and meter's
current so that voltage can be removed from the driving source to give
you the final R required to place that meter of 200ua' to full scale
when the reference is %100

Only the dedicated types, which I am sure he does not have, are
designed to directly accept the name plate energy sources, current or
voltage.

There are some meters like VU types for example, have a (I) requirement
point at 0 db scale, not full scale. The network needs to be calibrated
to fit that requirement and not full scale. It depends on the face scale
design.

I don't know what it is these days but we used to calibrate meters at
around 75% deflection.

Jamie
 
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