Gain 100 microAmp into 200 microAmp

[Bo-Lennart]

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

 

[JW]

On Fri, 29 Mar 2013 05:57:19 -0700 (PDT) Bo-Lennart
<bo-lennart.karlsson@telia.com> wrote in Message id:
<a3e10e2c-5f40-4415-b50a-1e3f2fb0c2e7@googlegroups.com>:

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_Cook]

Bo-Lennart <bo-lennart.karlsson@telia.com> wrote in message
news:a3e10e2c-5f40-4415-b50a-1e3f2fb0c2e7@googlegroups.com...
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

 

[Arfa Daily]

"Bo-Lennart" <bo-lennart.karlsson@telia.com> wrote in message
news:a3e10e2c-5f40-4415-b50a-1e3f2fb0c2e7@googlegroups.com...

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

I would have thought that it was pretty unlikely that it was actually
measuring 'current' as such. Much more likely that it is measuring output
voltage with a series resistor to determine its effective FS voltage. It may
well actually have a calibration pot somewhere on the board. Can you follow
the wires back to the board and see what the meter's "+" terminal actually
connects to ? if it is a series R or an R / VR combination, then you might
only need to reduce the value of the series resistor. If you measure the
resistance of the meter's coil, simple ohms law will determine the value
required

Arfa

 

[Jamie]

Bo-Lennart wrote:

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

 

[Arfa Daily]

"Jamie" <jamie_ka1lpa_not_valid_after_ka1lpa_@charter.net> wrote in message
news:7Ao5t.302144$KR.90262@newsfe27.iad...

Bo-Lennart wrote:

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.

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.

The driving circuit most likely has more than enough to accommodate that
200ua meter after recalculations.

On that score, I would agree

Arfa

Jamie

 

[Michael A. Terrell]

Arfa Daily wrote:

"Jamie" <jamie_ka1lpa_not_valid_after_ka1lpa_@charter.net> wrote in message
news:7Ao5t.302144$KR.90262@newsfe27.iad...
Bo-Lennart wrote:

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.

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.


The driving circuit most likely has more than enough to accommodate that
200ua meter after recalculations.

On that score, I would agree

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.


--

Politicians should only get paid if the budget is balanced, and there is
enough left over to pay them.

Sometimes Friday is just the fifth Monday of the week.

 

[Jamie]

Arfa Daily wrote:

"Jamie" <jamie_ka1lpa_not_valid_after_ka1lpa_@charter.net> wrote in
message news:7Ao5t.302144$KR.90262@newsfe27.iad...

Bo-Lennart wrote:

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.


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.


The driving circuit most likely has more than enough to accommodate
that 200ua meter after recalculations.


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

 

[Arfa Daily]

"Jamie" <jamie_ka1lpa_not_valid_after_ka1lpa_@charter.net> wrote in message
news:XnE5t.244145$Nq4.58225@newsfe21.iad...

Arfa Daily wrote:


"Jamie" <jamie_ka1lpa_not_valid_after_ka1lpa_@charter.net> wrote in
message news:7Ao5t.302144$KR.90262@newsfe27.iad...

Bo-Lennart wrote:

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.


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.


The driving circuit most likely has more than enough to accommodate
that 200ua meter after recalculations.


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

Oh, I don't dispute any of that. Of course, I accept that all moving coil
meters are current driven devices, no matter whether they ultimately display
in volts or amps. All that I was saying is that you only normally find a
shunt resistor, when the meter is in series with the load, and thus
genuinely reading some external circuit current. Unless the maximum current
that will be encountered happens to exactly match the FSD current of the
movement, then some of the actual current being measured will have to be
diverted away from the movement - 'shunted' if you like. However, when the
movement is hung across a voltage source, then it is measuring the voltage,
and a series resistor needs to be calculated, using the resistance and FSD
current of the movement, to limit the maximum current to the FSD current of
the movement, when the maximum voltage is being encountered.

From that, and from knowing that meters on test equipment such as AF
generators and AF mV meters are generally measuring a voltage level, rather
than any 'genuine' external circuit current, I came to the conclusion that
there was very likely to be a series resistor and / or pot to calibrate the
meter, rather than any kind of shunt resistor across the meter.

Arfa

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