Displacement sensors can measure different types of mechanical movement such as linear, angular, and rotary. A Rotary Variable Differential Transformer or RVDT has the same underlying working principle as an LVDT with modified design to measure rotary movement. An RVDT also uses a non-contact technology to ensure a longer life cycle and reliable measurement which is repeatable even when subject to the harshest working conditions.
What is an RVDT?
An RVDT is an electromechanical transformer that produces a linear output proportional to the angular displacement of the object being measured. The object’s angular movement is detected by the sensor and changed into electrical signals. RVDTs and LVDTs have similar working principles, but an RVDT has a cam core instead of an iron core. The sensor’s core will turn around the two coils using the rod or shaft.
Construction and function of an RVDT
The device consists of two coils or windings and a magnetic cam core connected to the shaft. A standard RVDT has an input voltage range of 3V RMS within the frequency range of 400Hz to 20kHz. Depending on how the shaft moves, the sensor can produce three conditions:
- Core at a null position
- Core moves clockwise
- Core rotates counter clockwise
When the core is at zero or null position, the differential output of the sensor is also zero. With clockwise rotation, the output of the sensor is positive, while counter clockwise rotations will result in negative differential output.
How to choose the right RVDT
A rotary variable differential transformer has many significant advantages over other sensor technologies. In selecting an RVDT, the following characteristics need to be considered.
- The accuracy of an RVDT is not perfect which does not make it suitable for high-precision applications.
- Working environment. RVDTs are robust and reliable and can work well in harsh conditions. This is a significant advantage of RVDTs over other types of sensors.
- Auxiliary power source. An RVDT relies on an AC power source to produce an output. If the application does not have a power source, an RVDT is not a suitable option.
- Compatibility with digital output. Many applications today prefer sensors that are compatible with digital output. The manufacturer can fit an RVDT to have this capability.
Apart from these parameters, the following are the advantages of using an RVDT:
- High measurement consistency
- Longer lifecycle
- Highly repeatable measurements
- Compact and strong assembly
- Infinite resolution
- Excellent linearity
- Wide dimension range
- Simple electronic parts
An RVDT produces a linear output which could be a limiting factor for its application; otherwise, it is an excellent choice for most industrial applications.
Applications of RVDTs
RVDTs are applied in control systems across several industries. Some specific examples are:
- Automotive brakes with cable systems
- Fuel control for engines
- Hydraulics and fuel valves
- Environmental control systems
These are only a few of the most common uses of an RVDT, but the non-contact design of this sensor makes it a preferred technology for many other applications such as in the mining and manufacturing sectors.