Piezoelectric preload force monitor

Hi all,

I am trying to read the "values" of two piezo load cells being preloaded simultaneously. The goal is to get them both preloaded with the same force.

I tried with classic circuit with resistor and analog input A0, but this may not be so simple. I read few articles about charge amplifier and would try with that, but if anyone has some more experiance or ideas what would be the best approach It would be really helpful. Thanks in advance.

circuit, datasheet(s), code?

Circuit and code I tried is "Arduino Knock". What I plan to wire and use the signal output from amplifier.

Op amp: TLV2771
Datasheet: https://www.ti.com/lit/gpn/tlv2771

circuit, all the datasheets, code?

Really, without knowing anything about these loadcells there's no way to proceeed.

Please read the sticky how to post threads, and provide all the information.

I'm going to print this out, hang it on the wall, stand back 5 meters and throw a dart at it, my answer will depend on what the dart hits. :slight_smile:

Hi guys, here is all information I have. For now I would like to somehow see the preload voltage rising to see the difference, once I have that I can read with Arduino and start with the code, but is should be just simple read analog and show on LCD.

  • Loadcell datasheet Download

  • Opamp datasheet Download

  • I can use Arduino Uno, Nano, Micro, but I am currently testing on Uno

  • Wiring I tried and piezo unloaded, loaded (force applied) analog input value is floating between range 0-90.

  • Wiring I plan to try and use opamp output with bias voltage

Do you realize piezo transducers only read dynamic loads? i.e. changing. Unless someone rewrote the law of physics, piezo transducers do not measure static loads.

Do you realize that such circuit exists? You preload and monitor the voltage so all piezos are preloaded with same force and when voltage drops back to before preload, job complete.

From the scant product pages these appear to be resistor-loaded piezo sensors, which need a high
impedance in the sensing circuitry - the specifications are given in V/N, suggesting this, as well as
the exictation voltage and current being listed.

You need a voltage amplifier with high input impedance, not that charge-mode amplifier, as the
data listed doesn't give charge sensitivity rating.

In fact a standard load-cell amplifier is probably intended as the readout device, though note
the high voltages quoted aren't compatible with 5V load-cell amps, but assume a +/-15V supply
(ie industry standard opamp circuitry). At 5V I'd suspect the dynamic range is limited, but the
sensitivity should be unchanged.

BTW I was worried by the SI values in this datasheet, as "500mV/lb +/-15%" is translated to
"112410 mV/kN" showing 3 spurious digits of precision - yes the numbers are at least right,
but it shows a worrying lack of basic numeracy for engineering/science to not understand
spurious precision. And why not say 112V/kN or 112mV/N?

I did do a sanity check on the other SI conversions and they seem to have got the values right
at least.

MarkT, thank you for very well explained datasheet. So I should use voltage amplifier and power supply voltage +15V/-15V. With the high impedance opamp, what should happen on op amp output? Raise voltage and then drop?

Rb is going to throw the scaling out completely. You want a high impedance input.

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