Re: HP Power Sensor wanted


Hi Chris,
The article you remember is there somewhere, I looked at it earlier this year, but cannot find it now. I think it was an Italian author, but I could be wrong.
The original circuit is simple enough, but when you read the HP guidance along the lines  "Don't reposition any of the wires, they were put where they are for a reason when we set it up" it is clear that maintaining isolation between the 10V chopper drive and the microvolt detector output is critical to a successful result. I did not find data for the chopper FETs that HP used but surely better are available 40 years on, ie RF types with very low capacitance. I was thinking I might  try an optically driven SPDT FET switch which might also have good isolation.

Ken  G3YKI

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