Volt Amp Ohm Meter


This is a hand-built test instrument which will measure Electrical resistance in Ohms, DC & AC voltage and DC & AC current.
It will also function as an electrical continuity tester (audio - buzzer).
It uses a commercial, purpose built, moving coil meter as a readout.
These were; I understand, sold by Electrical Supplier's, with the intent that a versatile measuring 'set' could be constructed.
The purchaser would have to calculate values of the various voltage multipliers, current shunts, resistance range multipliers etc when a multi-range/function is needed.
Sometimes popular radio/hobby magazines would publish a suitable design.
I obtained my example in a lot of surplus equipment I had accquired.
The meter appears to have been unused.
These "meters" were sometimes issued to trainee technicians as a project, with the idea that they must design and construct a useful functioning instrument.
This would reinforce their knowledge of DC theory, Ohms Law etc, and also develop their practical construction skills.

Information given on the meter face is:

Full scale deflection (FSD) 1 mA.
Meter coil resistance 100 ohm
Manufacturer Paton P/L Electrical Sydney (Aust)
Battery 1.5 volt (for resistance measurement)
My construction dates from c2003, I have since mislaid the mathematical working, but this is well covered in many standard textbooks.
I used E12 1 watt metal film resistors for range multipliers,
and eureka resistance wire for the low ohmage current shunts. (salvaged for a replacement immersion heater element, and terminated with an electrical strip connector)
Although built for nostalgic reasons, the instrument does as it should and although inferior to a modern DMM can be useful, none the less.