I bought me a big old 5A AC ammeter. (8" x 8")
I must admit I bought it thinking it was DC, but hey, I really only want it to match my old galvanometer :)
But I was thinking about the difference between an AC and a DC instrument.
Am I off track when I think that the AC ammeter is just a DC ammeter with a full wave rectifier and perhaps some smoothing electronics applied to the input before it is measured in millivolts across a shunt by the galvanometer inside?
"John Riley"
** Yikes !** It is almost bound to be a " moving iron " meter.
( Is the scale a bit cramped down at the low end ?? )
Such meters read DC amps of either polarity and AC amps accurately over a fairly narrow frequency range - typically up to a few hundred Hz.
....... Phil
Have a look at the beast at
I am only ever likely to try it around 30V DC with an amp or two charging my batteries.
The only AC might be mains 250V at 50Hz
"John Riley"
** It is Cleary a "moving iron" type - = look the term up on Google.The scale says it is calibrated at 50Hz.
...... Phil
To find out, you'd have to open the meter - it could be a "moving vane" type, which has two plates of magnetic material inside a coil, and one of them can rotate, which is connected to the needle. One of those will work on AC or DC, because the magnetic field induced in the vanes will be the same polarity in both, and they will repel each other.
Otherwise, it would have to be a bridge (with a suitable shunt), and they take care of the RMS/Average thing by scaling the meter dial.
Cheers! Rich
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