What is “RVDT”?
Rotary Variable Differential Transformer used for measuring angular displacement

01. Basic Structure

The key to the long life is simple & metallic structure

Magnetic flux transmission between the Stator Core and the Rotor Core enables contactless measurement of angular displacement.

RVDTs need less number of piece parts and are mainly composed of metallic parts. This structure is the key to long life (MTBF) and perfectly suitable for aircraft applications which require high reliability and environmental resistance.

Roles of Primary Winding & Secondary Winding

RVDTs have five lead wires, two for input and three for output.

02. Failure Detection

Magnetic flux generated in Primary Coil circulates around the Stator Core and the Rotor Core. The change of the magnetic flux passes through two-phase Secondary Winding is depending on the angular displacement of the Rotor Core.

Electrical Zero Position

The Rotor position, which equally divides the magnetic flux in the Secondary Winding and generates same the voltage of both Va and Vb, is defined as Electrical Zero Position.

Rotor Rotation

Rotor rotation changes the magnetic flux flow, and then Va / Vb voltage increases and decreases. Va / Vb voltage symmetrically increases and decreases each other.

Works for “Failure Detection”

Va / Vb voltage increases and decreases in proportion to the Rotor rotation. Summation voltage (Va+ Vb) shows steady voltage which does not depend on Rotor rotation. This characteristic can be used for Failure Detection in a variety of systems loaded onto aircrafts.

Aircrafts have various kinds of systems which use reciprocating movement in a limited angle, such as throttle levers, handles and pedals in Cockpit, and also flaps and spoilers outside of aircraft. For angle detection in these systems, RVDTs performs to the best of their potential.

Commercial Aircraft Applications

Business Jet Applications

Tips for Engineers: Ratiometric Calculation

RVDTs are generally used for Ratiometric calculation based on the Va / Vb voltage. With this ratiometric calculation, the sensing function becomes stable by mitigating effects from ambient temperature and excitation voltage.

Ratiometric value is the output characteristic changing proportionately according to the Rotor rotation. Using this characteristic, angle position of RVDT shaft can be detected as electrical angle.

03. Production

Produce various kinds of RVDTs

Tamagawa has a production line at 2nd plant located in Iida City (Nagano Prefecture in Japan). All processes of assembly and ATP (Acceptance Test Procedure) can be completed at this facility.

Tamagawa’s own production engineering automates the winding process in accordance with RVDT designs. This automated winding technology is one of Tamagawa's key technologies.