# Markings on analog moving coil meters...

Discussion in 'General Electronics Discussion' started by Externet, Jan 17, 2019.

1. ### Externet

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154
Aug 24, 2009
Hi.
V. A, VU meters usually have markings on the bottom of the scale. I suppose tell full scale current, internal resistance... Were to look for the meaning ? Is there a standard for markings ?
Several types:

2. ### Bluejets

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782
Oct 5, 2014
Ohms per volt is the meter impedance as seen by the test circuitry.
Other markings usually scale size and probably model numbers or manufacturer details.

3. ### Harald KappModeratorModerator

9,659
2,019
Nov 17, 2011
Also:
instrument class, e.g. KL. 2.5 meaning accuracy is 2.5 % of scale
Orientation of use, type of measurement etc. I found this page in German. Here's a table from the page with my translation:

davenn, (*steve*) and Externet like this.
4. ### Externet

732
154
Aug 24, 2009
That's it ! Thanks.

5. ### Colin Mitchell

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Aug 31, 2014
A meter that consists of a coil and pointer is called a MOVEMENT. And it has a certain sensitivity. Generally the sensitivity is 30uA or 10uA.
For a movement with a sensitivity of 30uA, it will take 30 microamps to defect the pointer full scale.
At this stage you cannot use the term OHMS PER VOLT. It is simply a MOVEMENT.
If you add a resistor in series with the coil, the movement will be turned into a VOLTMETER.
If a resistor is placed across the coil, it will be turned into an AMMETER.
When you create a VOLTMETER with a 30uA movement, and say you want a full scale reading of 10 volts, you want the 10 volts to create a current through the coil and series resistor of 30 microamps. At the moment we will neglect the resistance of the coil.
To get a current-flow of 30 microamps, we need a resistor of:
Now, without any calculator, we look at it this way: If the resistor is 10 ohms, the current will be 1 amp. If the resistor is 10k, the current will be 1mA. But we want one-third of a milliamp and so the resistor needs to be 30k.
A VU meter is generally connected to an amplifier circuit and the designer of the circuit will choose a movement or even a voltmeter or milliamp meter and connect it to the circuit and add resistors in either series or parallel until he gets the desired reading.
That's why a VU meter does not have a standard value. It's a movement that's adapted to the circuitry.