I have set up an FSR using the circuit defined here: Using an FSR | Force Sensitive Resistor (FSR) | Adafruit Learning System. The fsr does appear to work as expected in that as I add pressure, then vintage across the pull down resistor increases.
However I have been trying to calibrate the sensor by placing various weights in the sensor and recording voltage. What I have noticed is that if I put a fixed weight directly in the center, the voltage will continuously increase. I have seen this using various FSR sensors.
Is this something that has been observed by others and is expected or are there ways to ensure a more stable voltage readout.