Switching between 200V and Low Voltage Sensor 1

[garfayliu]

Hi all, I'm new here, so I'd like to thank anyone for their advice given.

I am having a problem trying to design a circuit to switch between connections to my piezoelectric device. Basically I can use it as an actuator and a sensor. Electrically I think a piezoelectric can be thought of as a small capacitor, with one electrode grounded and the other connected to the circuit.

At one point I want to actuate my device my applying 200V to it, at another point I want to be able measure voltages generated by my device (of the order of 500mV).

I am measuring my low voltages with data acquistion board which can only handle +/-10V inputs so obviously I cannot have that connected when I am actuating my device with 200V.

Does anyone have any suggestions/recommendations?

Solid state would be preferable, with switching frequencies ranging from 1Hz-1kHz, current should be low, <200mA but I've designed everything to handle 1A. I have tried using some fast switching relays which are digitally controlled, but they don't work, still looking into why.

 

[BrianR]

High power RF circuits use PIN diode switches for TX/RX switching, but I think you will get good results from a gate made from high voltage MOSFETS which will are very fast switches, followed by transient rated zener diodes across the logger i/p.

 

[Comcokid]

Your design issues are the same as used in depth sounders (i.e. fish finders) and in piezo level/distance measurement. I suggest you search within these areas for ideas. Generally, the receive chain starts with back-to-back diodes to limit the input, and a high gain amplifier stage that can quickly recover from saturation. The piezo element itself tends to ring after excitation which makes the recovery time of the receive input stage less important.