Fundamentals of Sensing and Signal Conditioning

Summary

The first element in a classic electronic measuring system is the sensor. This chapter categorizes sensors depending on the electrical quantity at their output: voltage, current, charge, resistance and reactance. This categorization is not the only applicable one, but it allows us to treat signal conditioning at the same time as sensors. The electrical representation of a sensor might be a Thevenin‐type equivalent circuit including a series impedance. The internal impedance of the sensor is represented by Z_c and determines the voltage drop between e(m) and V_s when a load is attached, if the current I_s is negligible. A variety of techniques exists for the conditioning of electrical signals coming from charge‐based sensors. A useful idea is that if a capacitor is storing a certain charge, there is a resulting voltage on its terminals and vice versa. This can be exploited at the sensor itself via a very high impedance amplifier.