[TCML] Meters (was Variac)
skip at ladybughell.com
Fri Oct 24 12:14:41 MDT 2008
Here is a brief AC meter tutorial.
AC Volt meters:
They measure voltage and do not know or care about current. Meters
can be readily found with a 150 or 250 Volt scales as appropriate for
Similarly to the Voltmeters, these know nothing and care nothing
about the voltage up to a certain HV point. These measure
current. These can be readily found that can measure up to about 20
amps without any shunts or current transformers. Beyond about 20
Amps, you would normally use a current transformer with a standard AC
Ammeter. These current transformers are described in a ratio
relating the rated input and output current. For example, a
transformer might be described as 100:5. In this case, with 100 amps
input, you get 5 Amps output. This would usually be directly
connected to a meter rated for 5 Amps full scale. It would have a
face showing 100 amps full scale. It would also be possible to add a
low ohm resistor in series with the meter and transformer that could
be connected to an oscilloscope for waveform viewing. This would be
useful to optimise your power factor which will minimize the current draw.
Just for the fun of it, I have installed a pair of 100:5 current
transformers and 5 Amp meters with 100 Amp scales on my house AC in
my circuit breaker panel. It is interesting some times.
Meters and current transformers of these types are readily often
available on Ebay.
I have a few 100:5 current transformers that I am not using if anyone
is interested. I can also provide any custom current transformers
for smaller currents that could be made to work with almost any DC
meter that you may have laying around.
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