Compensation with electronic network

Intelligent transmitters have two major components (1) a sensor module which comprises the process connections and sensor assembly, and (2) a two-compartment electronics housing with a terminal block and an electronics module that contains signal conditioning circuits and a microprocessor. Figure 6.9 illustrates how the primary output signal is compensated for errors caused in pressure-sensor temperature. An internal sensor measures the temperature of the pressure sensor. This measurement is fed into the microprocessor where the primary measurement signal is appropriately corrected. This temperature measurement is also transmitted to receivers over the communications network. 

Fig. 11.6. Simple feedback electronics with integration compensation. The first op-amp amplifies the error signal with a variable gain. An RC network provides an integration compensation. A high-voltage op-amp provides an output of 100 V or more, to drive the z piezo.

In the days of linear, continuous electronics non-linearity was a major problem. Such compensation techniques as were available were based on diode networks having reciprocal characteristics, but by their nature these were relatively crude. As a result all non-linear primary sensor mechanisms tended to be ignored. Now, linearisation processes such as look-up tables or polynomials are easily realisable with digital electronics. 

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