Wind Systems

Towers, turbines, gearboxes; processes for shaping and finishing component parts.

3D Scanners

A white paper to assist in the evaluation of 3D scanning hardware solutions.

Negotiate Your Salary

Learn the best principles to negotiate the salary you deserve!

Machine Design

How-to, in-depth technical articles for machine design engineers

more free magazines

The Rotational Variable Differential Transformer (RVDT) is used to measure rotational angles and operates under the same principles as the LVDT sensor. Whereas the LVDT uses a cylindrical iron core, the RVDT uses a rotary ferromagnetic core. A schematic is shown below.

Typical RVDT Sensor
Common Specifications

Common specifications for commercially available RVDT's are listed below:

  Input: Power input is a 3 to 15 V (rms) sine wave with a frequency between 60 to 20,000 Hz.
  Angle: Capable of continuous rotational measurement. However, most RVDTs have effective angle limits of up to ±60°.
  Nonlinearity: Higher accuracy in the smaller angle range: 0.25% @ ±30°, 0.50% @ ±40°, 1.50% @ ±60°.
Pros and Cons

  • Pros:
  - Relative low cost due to its popularity.
  - Solid and robust, capable of working in a wide variety of environments.
  - No friction resistance, since the iron core does not contact the transformer coils, resulting in an very long service life.
  - High signal to noise ratio and low output impedance.
  - Negligible hysteresis.
  - Infinitesimal theoretical resolution. In reality, angle resolution is limited by the resolution of the amplifiers and voltage meters used to process the output signal.
  - No permanent damage to the RVDT if measurements exceed the designed range.
  • Cons:
  - The core must be in contact (directly or indirectly) with the measured surface which is not always possible or desirable.