This instrument is Linear Voltage Differential Transformer. It is an inductive transducer. Also known as LVDT. For measuring displacement of any object we use them. It uses the basic transformer principle of mutual inductance to measure linear movement. LVDT is a passive transducer having coils and an alternating magnetic field which produces an analog output voltage. It measures the distance along the linear axis.
The above figure shows a transformer with one primary and two secondary coils. The magnetic flux produced by primary winding is coupled to secondary windings through the core. There is a movable soft iron ferromagnetic core placed in the centre of two secondary coils. The two secondaries are wound 180o out of phase. The two induced emf in the secondaries cancel out each other as Es1 = Es2. The output voltage of the secondary is zero. Since core is at the center and the voltage distribution is equal.
At null or centre position of core large flux is induce in one of the secondary windings. As a result of which imbalance occurs and it becomes out of phase. The voltage induced in the secondary winding near to the core is more compared to the voltage induced in secondary winding away from the core. This imbalance produces some output voltage. The differential output is of LVDT is
Eo= Es1 – Es2
LVDTs have low hysteresis loss. They do not have any frictional loss. The LVDT have high value of output and hence do not need any amplification. They have high range of measurement of displacements.
Application of LVDT
In industries we find application of LVDT as pressure transducer. They also used as null position sensors in servo systems.
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