I have done some more work today on the current amplifier and found that I did not have the input turned up to a high enough voltage to obtain the full 1A output, so I have now repeated the test and monitored the heat output from the amplifier.


Heat output at 1A

This is still just within the nominal operating temperature specified for the op-amp, but it was still climbing slowly when turned off. When switched back down to a 0.5A output, the temperature does start to drop away quite rapidly.


With this completed, I decided to do a few quick tests with a 20 turn coil and a CM55 current clamp as shown below.


{gallery} CM55 current clamp tests

0.5A 50Hz test

10A reading expected on clamp meter

1A 50Hz test

20A reading expected on clamp meter

1A 5kHz test

Clamp meter taken beyond frequency specification

The first two tests show the clamp meter with the expected readings for a 50Hz input into the 20 turn coil. The frequency was then raised in the third picture and you can see that the current reading drops right off. For a Rogowski style clamp, the CM55 actually has quite a poor bandwidth.


My next stage with the current amplifier will be to try and figure out a way of measuring the input and output of the coils with the equipment I have, to see if there is any frequency drop off across the coil.


I have collected some impedance data for each of the coils I have wound using an LCR meter.


Coil impedance measurement data

Impedance at 50Hz Impedance at 40kHz

The data shows the increasing impedance of the coil as the frequency is increased. This may give issues with being able to reach the full output current using the existing amplifier design.