D
[email protected]
- Jan 1, 1970
- 0
I got a call from a company who was having problems getting an AC
current regulator working. They just needed some basic ideas. I often
get such calls and I try to help as long as it doesn't take up too
much of my time.
As near as I can tell, they are using the current to test and calibrate
current transformers. They needed to route 10 amps of pure 60Hz sine
wave AC current through a single heavy wire, as part of a calibration
circuit for one of their products. They said the total resistance of
the loop was about 0.025 ohms. Their first approach used a small
variac and a toroid transformer, to produce the needed current.
However, it was not well regulated. The variac approach worked fine,
as long as the line voltage remained at 120vac. But since they wanted
to keep the 10 amps to an accuracy of +-0.5%, any line voltage change
would certainly change the current. They considered attaching the
Variac to the output of a ferro-resonant constant 120vac supply or use
a motorized Variac but they really wanted something much more compact.
They were also concerned about distortion of the 60Hz waveform coming
from wall outlet, especially at the waveform peaks. I suggested that
perhaps a cleaner 60Hz signal could be synthetically generated and used
as a reference. The signal would be fed to an audio amp, which would
drive the winding of a low voltage transformer, perhaps 24vac. A
custom wound secondary of the transformer could then generate the
needed high current. By using another current transformer in line with
the test loop, in conjunction with an op amp circuit, the AC current in
the loop of wire could be kept constant. Can anyone think of another
way this could be done?
David A. Johnson, P.E. --- Consulting Engineer
http://www.djandassoc.com
http://www.imagineeringezine.com Home of the Imagineering on-line
magazine.
Also, http://www.discovercircuits.com A collection of over 11,000
schematics.
current regulator working. They just needed some basic ideas. I often
get such calls and I try to help as long as it doesn't take up too
much of my time.
As near as I can tell, they are using the current to test and calibrate
current transformers. They needed to route 10 amps of pure 60Hz sine
wave AC current through a single heavy wire, as part of a calibration
circuit for one of their products. They said the total resistance of
the loop was about 0.025 ohms. Their first approach used a small
variac and a toroid transformer, to produce the needed current.
However, it was not well regulated. The variac approach worked fine,
as long as the line voltage remained at 120vac. But since they wanted
to keep the 10 amps to an accuracy of +-0.5%, any line voltage change
would certainly change the current. They considered attaching the
Variac to the output of a ferro-resonant constant 120vac supply or use
a motorized Variac but they really wanted something much more compact.
They were also concerned about distortion of the 60Hz waveform coming
from wall outlet, especially at the waveform peaks. I suggested that
perhaps a cleaner 60Hz signal could be synthetically generated and used
as a reference. The signal would be fed to an audio amp, which would
drive the winding of a low voltage transformer, perhaps 24vac. A
custom wound secondary of the transformer could then generate the
needed high current. By using another current transformer in line with
the test loop, in conjunction with an op amp circuit, the AC current in
the loop of wire could be kept constant. Can anyone think of another
way this could be done?
David A. Johnson, P.E. --- Consulting Engineer
http://www.djandassoc.com
http://www.imagineeringezine.com Home of the Imagineering on-line
magazine.
Also, http://www.discovercircuits.com A collection of over 11,000
schematics.