Chapter 7 – Variable Conversion

The chapter considers how to deal with outputs from a measurement sensor that are not in the form of a readily measurable voltage signal. Such outputs include translational displacement change outputs, changes in various electrical parameters such as resistance, inductance, capacitance, and current, and changes in the phase or frequency of an alternating electrical signal. Translational displacement changes are dealt with later in Chapter 19 and so this chapter only considers the variable conversion elements and other techniques that are used to convert nonvoltage electrical parameter outputs into a more convenient form. Electrical bridge circuits are particularly an important type of variable conversion element and are considered in some detail. This discussion covers both DC and AC types of bridge, in both null and deflection forms. The chapter then continues by looking at other ways of dealing with nonvoltage sensor outputs in the form of resistance change, inductance change, capacitance change, or current-magnitude change. Finally, it looks at ways of interpreting the outputs of sensors that are in the form of a change in either the frequency or the phase of an electrical signal.