SSL db Meter ma test ?

[tubemonkey35]

I found a place with some meters, but none have markings other than they are db meters. I should be able to test to find a 1ma one with my voltmeter correct?

 

[Mark Burnley]

Hi,

Check my "Mystery Meters" link at the bottom of my post here
to work out the meter sensitivity:

:thumb:

Mark

 

[tubemonkey35]

thanks

 

[PRR]

> some meters, but none have markings other than they are db meters. I should be able to test to find a 1ma one with my voltmeter correct?

By measuring what?

I can do it with my ohm-meter, but I know what comes out of it.

You actually don't need another meter: the meter IS a meter (duh).

Mark posted some good techniques. What I'd really do is take a 1.5V battery and some resistors like 30K, 15K and 1.5K. Put the 15K, the 1.5V, and the mystery meter in series. That flows 1.5V/15K= 0.1mA or 100uA through the meter. If it goes backward, switch some wires. If it goes just to full-scale, it is a 100uA meter. If it pins, try 30K (50uA). If it only goes to 1/10th, try the 1.5K resistor (1mA).

True, with this cheap technique there is error from weak battery, 10% resistors, and the small resistance of the meter. Unless the battery is dead, the answer will be close-enough. Unless the meter has been badly abused (and unreliable), the full scale sensitivity will BE some nice round number like 100uA; they don't make 91uA meters. If you really need to know exactly, of course you use a sensitive amp-meter as Mark describes.

Most meters with pretentions of being "VU-ish" are 200uA (will read half-scale with 1.5V 15K). If your plan calls for a 1mA, and has a resistor in series with the meter, try a resistor 5 times bigger. This will work in the SSL limiter: you can use any meter 50uA to 10mA by scaling the meter resistor.

 

[tubemonkey35]

thanks PRR

 

[Mark Burnley]

Hi Tubemonkey35,

See if this diagram makes it clearer:

...as PRR points out the DMM is not essential- but it helps you to "see" what's going on. Meters are made with standard-ish sensitivities, 50uA, 100uA, 500uA and 1mA being common. Use a 7k5 resistor for a 200uA range (a common meter sensitivity for a VU meter)

:thumb:

Mark

 

[tubemonkey35]

cool! Thanks to all.

 

[dukasound]

Most meters with pretentions of being "VU-ish" are 200uA (will read half-scale with 1.5V 15K). If your plan calls for a 1mA, and has a resistor in series with the meter, try a resistor 5 times bigger. This will work in the SSL limiter: you can use any meter 50uA to 10mA by scaling the meter resistor.

Thanks PRR for explanations (like allways).
I think mine VU is 250uA. Is it mean I must use about (4 x 2K) 8K in SSL circuit?
Duka

 

[gyraf]

yes