Hi Greg,

On 16-Oct-03, Greg Mayman wrote to George White:

 GW>> Cost! :-(. A supressed zero voltmeter is cheap and easy to wire,
 GW>> just a wire from somewhere just after the ignition switched
 GW>> point. An

 GM> Yes, I think that is the main reason.

 GW>> ammeter has the extra cost (probably more then the cost of the
 GW>> meter) of a high capacity shunt in the main feed to/from the
 GW>> battery (which

 GM> Usually!

 GM> But I have several articles from electronic magazines dating back
 GM> to 1981 for ammeters that work by measuring the voltage drop along
 GM> the existing battery negative cable.

However this is not usually practical in a production environment.
There are too many variables in the installation for it to work
without individual vehicle calibration, a No-No for volume production!

 GM> This does not require heavy connecting wires or additional shunts,

True... But for production to get acceptable accuracy, due to the
vagarities of connection resistance, a shunt is a necessity :-(.

 GM> and also allows the meter to display the starter motor current!

Not something that's really of interest, all it tells you normally is
how thick the engine oil is (== how cold the engine is).

 GM> The original article used a grounded-base dual transistor
 GM> amplifier feeding a centre-zero moving-coil meter with diode
 GM> shunts across it to compress the high current ends of the scale.
 GM> Very elegant!

Hmmm.... Grounded base? I'd need to see the circuits to work that one
out! However I can think of several ways of doing it, just none of
them suitable for volume production.

George

--- Terminate 5.00/Pro