Meter used before digital meter?

kooombaya

I didn't know where to post this question which is:
What type of meter, which had very good loading characteristics, were used to measure voltages before digital meters were produced?

I tried googling but it's all a jumble. can anyone guide me? thanks.

Edit: is it a voltmeter?

berkeman

Certainly it's a voltmeter, but I seem to recall that it had a special name when it had a high input impedance.

This is a school question, right? I'll try to see if I can figure it out, but if I do, I can only offer hints to help you search... Makes sense?

berkeman

Okay, the Wikipedia article on Voltmeter has your answer in it. Does that help?


EDIT -- BTW, rather than searching the whole web with Google, often a search at Wikipedia will get you a technical answer quicker. Other tricks are to use Google Images (no help for this question), or add the word tutorial after your search terms in Google (also no help in this particular case).

kooombaya

thanks i'll reread the wiki article.

Edit: Am I correct in saying it's the VTVM?

supratim1

or a galvanometer could be converted to voltmeter using a high resistance in series.

kooombaya

So were galvonometers invented before voltemeters? Is that it? Im sooooooooo confused -_-

berkeman

The VTVM used vacuum tubes, but yes it had high input impedance. I like the FET-VOM better, since that was one of the first meters I used. Kind of rolls off the tongue...

kooombaya

:)

:)

I-Caramba!

Oh hi there :) I wish to understand this question as well!

turbo

Have you Googled Simpson meters? They have been in business for about 90 years. When I was working in pulp and paper mills the field electricians would check components with their Flukes, etc, but when the components came back to the shop they would be hooked up to Simpsons.

CWatters

Kooombya - Not quite sure what you are asking but....

Early analogue meters were originally powered by the signal they were trying to measure. When you connected them to a voltage source a current flowed through the meter coil causing it to try and rotate against the return spring. The coil impedance needed to be high enough to prevent the meter loading the circuit but low enough that sufficient current flowed to provide the torque needed to turn the movement. It was a compromise and the coil impedance could never be really large so there was allways some loading effect. You had to get good at working out when that was significant and correcting measurements to take into account.

When I went to collage (1979) you could buy multimeters in Tandy that were battery powered and used a FET amplifier to prevent the meter loading up the circuit. They were still called Multimeters although perhaps more correctly they were FET VOM's

Example..

http://www.radiomuseum.org/r/radio_s..._cat_no_2.html

I still have mine (from about 1980) in it's original box and it still works just fine.

PS: One problem I found was that when working on a radio transmitter the radio signal could be picked up inside the meter somewhere and stop the meter working. Usually easy to spot because the needle would typically try to go backwards to the stop.

I-Caramba!

Could you explain what input impedance is and how it can be found?

CWatters

http://en.wikipedia.org/wiki/Input_impedance

I-Caramba!

I have looked at the already, and I still don't understand.

ehild

Do not forget the potentiometer as measuring instrument to measure voltage. It has the advantage that draws practically zero current.

http://en.wikipedia.org/wiki/Potenti..._instrument%29

ehild

CWatters

The input impedance of a system stage describes what it "looks like" to the preceeding stage. If you like you can call it the load that the previous stage has to drive.

Consider an 8 Ohm Loud speaker. The simplest model of a loud speaker is an 8 Ohm resistor and in that case the input impedance would be 8 Ohms. However real loudspeakers are not quite that simple.