So, I got this circuit, my sensor is a piezoceramic disk and I use small round ball of steel to impact the piezo.
The problem is when i connect the OpAmp the signal is offset and this offset increase with multiple impact.
I just dont know why this happen and how to solve that.
Jonathan,
This is classic capacitor clamp behaviour.
Note the that maximum negative voltage is the same for both impacts. That's the clamp in action.
You need a DC bleed (bias) resistor otherwise the input can float to any voltage.
Connect the resistor to a positive voltage to prevent clamping the negative peaks.
Hi,
I try to put resistor 100M 10M 1M for bleed but the offset is still there, when i shoot 1 ball or many at the same time the result is the same, but on 1 impact the signal look like a capacitor discharge. I measure the Piezo capacitance it is 2.6nF. On the picture I use 1M bleed resistor.
I want to feed the signal the a ADC, I don't want the negative voltage , I only need the positive peak to measure the force of the impact.
Jonathan,
Do you need a peak detector to hold the peak voltage for the ADC or is the ADC read fast enough to capture the peak in real time?
This circuit will not shift DC bias with strikes.
Jonathan,
With peak detector and reset. Reset could be replaced with bleed resistor.
