On Sat, 03 Jan 2009 21:52:52 GMT, nicola wrote:

On Sat 03 Jan 14:16, Stuart wrote

In article ,
nicola wrote:

(Q1) Under "DC CURRENT" my user guide says, "voltage drop: 200
mV". Is this the disturbance in a circuit when measuring DC
current?

It is the volt drop across the meter at "full scale deflection".

If you measure 2mA on the 2mA range it will cause a 200mV drop.
If you measure 2mA on the 20mA range it will cause 20mV drop.

Oh! Now that isn't what I was expecting.

I read what others have posted about the meter being based arounf
a voltmeter which reads 200 mV at full scale.

I had inferred that the full scale deflection reading was
dependent on the range chosen.

So, for example, the full scale reading on a 20 mA range would be
20 mA. (On the 2mA range it would be 2 mA.) And I then had the
impression that when reading almost 20 mA on the 20 mA range, I
would get the 200 mV drop mentioned in the specs.

Is that understanding wrong?

nikk


No - it is correct.

The meter has a voltage drop of 200 mV at full scale - internally, it
is a 200 mV full scale meter.

If you measure a current of 2 mA on the 2 mA scale, the meter will
have a 200 mV voltage drop.

If you switch to the 20 mA scale, that 2 mA current will result in a
20 mV drop.

If you switch to the 200 mA scale, the 2 mA current will result in a 2
mV drop.

For any scale and current, the meter's voltage drop is:
(current/full_scale) * 200 mV


--
Peter Bennett, VE7CEI
peterbb4 (at) interchange.ubc.ca
GPS and NMEA info: http://vancouver-webpages.com/peter
Vancouver Power Squadron: http://vancouver.powersquadron.ca