You mean current transformer? A clamp is one of my vices:
[A play on word there ]
The easiest is another transformer!
You have two problems:
- You need a high impedance controlled current source (so that the internal burden resistor can do its stuff of turning the current into a voltage - if you need to verify the action of the burden) - or you need a controlled voltage.
- That current or voltage source needs to be floating - i.e. not have a ground reference.
Having appropriate test gear and a well-stocked “parts” box, I’d use a low voltage isolating transformer and a fixed resistor and rheostat in series - the rheostat to provide some measure of control of current, and the fixed resistor to limit the current to whatever the burden expects - 50 mA in the case of the emonTx.
Notice I say “rheostat” rather than “potentiometer”. The difference is a rheostat is designed to draw current from the moving contact, a pot isn’t.
If it’s important to you to control the current between zero (rather than a small value) and the maximum, then you could use a heavy wirewound potentiometer to shunt the current away from the burden, rather than in series with it (still using the fixed resistor to limit the current).
I just use the test rig from the test report on the c.t., using as many primary turns through the c.t. as I need to give the current I want to represent.