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Blocking cap recmds for 42941A in-ckt testing of PZT cells

Question asked by ftsolutions on Jul 21, 2008
I am testing PZT actuators which are mounted and wirebonded into an electro-mechanical device, and am using the 42941A probe to perform impedance measurements in-situ.  The pin probe head has been working pretty well for this.  I have determined that I need to perform tests with externally applied DC bias voltage to the circuit and/or have the circuit powered, and am looking for information on the best way to implement DC blocking to the probe to avoid damage and to minimize added error.   The DC voltage will exceed the capability of the probe and the nominal capacitance of the PZT cells are in the<500pF range.  I am presently considering using the BNC adapter to connect to a PCB coax connector, and to mount caps on the PCB along with the terminals for the DC power supply connection, and attach short probes from the PCB.  Since my PZT's frequency range of interest is from 60Hz-2MHz, these caps are going to have to be pretty big, unfortunately.   Any recommendations or suggestions are welcomed.  Thank you.