AC and meter movements

 

How does one use AC to actuate a D'Arsonval (Weston) meter movement? Is a
single rectifier sufficient? Bridge?

Movement of interest says "FS = 45.8 uA DC".

Extra points for links to drive circuits.

Thanks.

 


"Mike Cook"


** The simplest possible AC converter circuit use two germanium diodes, one
wired across and one in series with the meter.  This is what most anlogue
multimeters use for the AC volts ranges.

However, the sky is the limit if you go for active circuits using FETs,
op-amps and even special AC to DC converter ICs that compute the "true rms"
value of all manner of AC waveforms.



....   Phil

 


Thanks Phil for the simple answer.

This is for measuring output of a simple variac, so yes, the germaniums seem
to be the answer.

Regards,
M

 

wrote:


Small schottkies will behave about the same. If you use a big series
resistor, as you will in this case, any diode will work.

John

 


- meter movement: 968 ohms; 45.8µA DC full-scale
- for 140V AC full scale, V = 0.443344, in V mode: series R = 3046120.5 ohms
- for 15A AC full scale, V = 0.443344, in A mode: shunt R =29.5 milliohms

I didn't take into account the diode drops. Should I? Where?

This is a variac in "boost" mode (hence the max value of 140V).

Thanks.