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measuring current

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hpibmx:
Hi :)

I'd like to measure both mA and A for my motherboards consumptions,
so is there anyway wire both analog ammeter without burning them? I need them both as i need to monitor the startup ma and the standby consumption.  :-BROKE

thank you in advance.

Kleinstein:
Combining the 2 meters is not that easy. Depending on the details of the meters it could be done by adding anti-parallel schottky diode to the mA meter to clamp the voltage / signal and than have them in series. However the voltage loss / burden voltage may still be too high for the computer to work. The probably better choice would be unsing only the shunt from the A meter and than add a custom amplification for the low range. This may than need a different meter for the low range (may use the old one by removing the shunt).

Doctorandus_P:
It is more common to use just one meter, and then add some circuitry to switch between different ranges. quite similar to the old analog Multimeters, that use a single pointer with many current, voltage, and resistance ranges.

TimFox:
Another method is to build an analog logarithmic amplifier to measure the voltage across a shunt resistor.
This is not easy to build, but it is straightforward to calibrate the indicated voltage output as a function of input voltage/current.
The ancient (ca. 1970)  -hp- 7562A and 7563A logarithmic units can be found at surplus sites:  the 7562A includes a true-RMS converter, and is capable of AC or DC input.  The 7563A is DC only.
The 7563A has a dynamic range of 110 dB (3.2 x 105 V/V), and a rise time of 2 ms (input < 1 mV) decreasing to 40 us (input > 10 mV) and 2 us (input > 1 V).
It has a single input range, but you need to select positive or negative input voltage.

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