Questions about a strain-gage amplifier circuit

[doncarlosalbatros]

I'm trying a build a strain gauge amplifier using this instrumentation amplifier: https://www.analog.com/media/en/technical-documentation/data-sheets/AD8221.pdf
Bridge is 350 Ohm full bridge and with a 5V excitation voltage.
The strain gage will be outputting +-2mV only.

After making some research I finalized the circuit as below:



The wires from gages to the amplifier will be around 15 meters long.

I would be glad to have your opinion about this circuit.
I have some questions in my mind and couldnt find an answer yet,

1-) How can I add some ESD protection and where in the circuit and which type of diode should I use? Any models which wouldnt effect the gage signals?
2-)I added RFI filter because this paper suggests: https://www.analog.com/media/en/technical-documentation/application-notes/AN-671.pdf Would that be enough for input signal noise? Should the wires be twisted?
3-)I want to use a RC LP filter before the data acquisition ADC. But should that filter be right after the inamp output or close to the ADC?
4-)+-5V voltage converter is a bit noisy in simulation and are the caps in this circuit enough for noise?
5-) I might need to make this circuit more versatile like adjustable gain or adjustable reference offset. But the pot I need to use must be very price to have a stable gain. And for the reference they warn not to use voltage divider. What IC I can use to adjust the ref voltage here? One of my fear is if I dont add a variable reference or gain and if they install the gage under a stress then my amplfiier in the schematic might saturate.

If you have any experience and extra suggestions I would be glad to hear. Thanks

 

[KlausST]

Hi,

1) any signal diodes will do. If you need high precision, then use "low leakage diodes". If you need even more precision, then connect two diodes anti parallel to 2.5V bias voltage.
2) cutoff frequency of RF filter may be optimized to your max signal frequency range.
Twisted wires: I recommend twisted wires, in a shielded cable.
3) capacitor close to ADC. R is not critical.
Do you have a +/- input ADC? If not you need to bias your INA output.
4) use an RC filter between DCDC and INA.
5) Gain in microcontroller. Offset in microcontroller. Don't use pots. Select gain that the INA doesn´t saturate.

What ADC are you using?
What resolution, precision and accuracy do you expect? (Values please.)

Klaus