|
A question was posted to the Syn-Aud-Con
listserv about how a voltage divider could be constructed to measure
the AC line voltage from a wall outlet using a TEF
analyzer. Jim Brown responded:
All you need is a simple voltage divider that doesn't load the
transformer beyond it's rating. Look at the current rating of the
transformer. Make the total series resistance draw about one tenth
of the rating of the transformer. This reduces non linearity within
the transformer due to core saturation.
Set the divider ratio (R2 divided by R1 + R2) equal to 0.5v divided
by 6.3 volts (or whatever the output voltage of the transformer
is). R1 is the input resistor, R2 is the output resistor. You should
end up with R2 being about 1/10 of R1 for the voltage ratio noted.
A very good text in basic electronics like this is the Radio Amateur's
Handbook, published by the American
Radio Relay League (ARRL). There is a new edition every year
but, as the old-timer who taught me radio 40 years ago told me when
I asked why his handbook was 20 years old, "Ohm's Law doesn't
change."
This classic text is well written, easy to understand, and uses
just enough math to let you learn the basic equations for calculating
the impedance of coils and capacitors. It also has great practical
information on antennas and coaxial feedlines such as those you
would use for wireless mic systems.
Now that you have your test set built, calibrate the TEF to it
by plugging the proper constant in at the TEF calibration menu.
You could find the constant by multiplying the step- down ratio
of the transformer (6.3/120) by the voltage divider ratio (.08),
yielding a constant of 0.0042 volts equal 1 volt. But both of these
depend on the tolerances of the components used (i.e., the resistors
and the transformer).
A better way is measure the same steady state line voltage with
a meter of known accuracy and with the TEF machine using a constant
of 1. Then divide the two numbers and use that value for the constant.
Your accuracy will now be as good as the meter you used to measure
the line voltage."
 |
|
You
may also want to read these related stories:
|
|
|
