EMI510 - Inductive Transducer

EMI510 - Inductive Transducer Inductive transducers may be either of the self generating or the passive type. The self generating type utilizes the basic electrical generator principle, i.e. a motion between a conductor and magnetic field induces a voltage in the conductor (generator action). This relative motion between the field and the conductor is supplied by changes in the measured. An inductive electromechanical transducer is a device that converts physical motion (position change) into a change in inductance. Transducers of the variable inductance type work upon one of the following principles. Variation of self inductance Variation of mutual inductance Inductive transducers are mainly used for the measurement of displacement. The displacement to be measured is arranged to cause variation in any of three variables Number of turns Geometric configuration Permeability of the magnetic material or magnetic circuits Variable Reluctance Type Transducer A transducer of the variable type consists of a coil wound on a ferromagnetic core. The displacement which is to be measured is applied to a ferromagnetic target. The target does not have any physical contact with the core on which it is mounted. The core and the target are separated by an air gap, as shown in Fig. Differential Output Transducers Normally the change in self inductance, ΔL, for inductive transducers, (working on the principle of change of self inductance) is not sufficient for detection of subsequent stages of the instrumentation system. However, if successive stages of the instrument respond to ΔL or ΔM, rather than L + ΔL, or M + ΔM, the sensitivity and accuracy will be much higher. The transducers can be designed to provide two outputs, one of which represents inductance (self or mutual) and the other the decrease in inductance (self or mutual). The succeeding stages of the instrumentation system measure the difference between these outputs. This is known as differential output. Advantages of Differential Output Sensitivity and accuracy are increased. Output is less affected by external magnetic fi elds. Effective variations due to temperature changes are reduced. Effects of change in supply voltages and frequency are reduced.