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The letters R.V.D.T stand for Rotary Variable Differential Transformer.
Principle of operation
The RVDT is a variation on the LVDT sensor and works on almost the same electrical principle, except that the core rotates within the circular winding assembly instead of moving longitudinally. The sensor design consists of an assembly of one primary and two secondary coils wound on a circular bobbin. A separate core is mounted on a shaft that rotates within the coils. The primary winding is energised with a constant amplitude A.C. voltage and this produces an alternating magnetic field in the centre of the winding assembly, which induces a voltage signal in the secondary windings dependant on the angular position of the core. Rotating the core within the coils causes the secondary signal to change. As the two secondary windings are positioned and connected in push-pull mode, when the core is at the centre of the winding assembly, a zero signal is derived (null voltage). Rotation of the core from the centre in either direction causes the signal to increase. The precision wound coils create an output signal with a linear relationship to the rotational movement of the core.
The advantage of using a RVDT is that the rotating core makes no electrical contact with the winding assembly so is ideal for applications where minimal mechanical friction is required. Additionally, RVDT sensors can be constructed from materials designed to withstand temperatures up to 180°C (356°F).
As the RVDT sensor is an inductive device, the primary coil is energised from an AC signal source (oscillator circuit), which then creates the induced voltages in the secondary coils. An additional circuit then converts (demodulates) the secondary voltages to a usable measurement signal. RVDT sensor models are also available with integral signal conditioning circuits (electronics).
The usable measurement range of a RVDT sensor is limited to approximately ± 50° (100°) and is most accurate over ± 30°. The accuracy decreases as the measurement range increases, after which you reach a point where the output becomes very non-linear. RVDT sensors are available in various housing diameters, typically servo size 08, 09 and 11, with have a number of mounting options including servo and body flange.
Active Sensors have a team of engineers with specific RVDT design and manufacturing capabilities and would welcome the opportunity to discuss your application in more detail. If you have a technical question regarding the suitability of RVDT sensors for your measurement system, please contact us.