Quote:
Originally Posted by JThiessen
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Why two meters, as opposed to measuring individually with one meter? I ask, because I tried measuring the current with my Fluke (I just stuck the probes into the wires). The numbers it showed didn't make sense to me at the time (remember, I was on a 10 day drinking binge....  ). |
Because the method for meter hookup is different for voltage and current.
In voltage mode, the meter is hooked in
parallel with (or "across") the component to measure. Meters in this mode have a high internal resistance to avoid it having an effect on the circuit being measured. This also means if you hook it in series with the measured component, you are introducing a very high resistance (in the mega ohms) into the circuit and things won't work right (you'd have a voltage divider with the vast majority of the supply voltage being dropped on the meter).
In current mode, the meter is hooked in
series (or inline) with the component being measured. Meters in this mode have a very very low resistance (shunt), just enough to cause a voltage drop in the milli-volts when current flows through it. If you place the meter in
parallel with the component being measured, you are effectively shorting it out and/or blowing the protection fuse in the meter.
So yeah, you kinda need two meters if you want to see voltage and current numbers at the same time.