Rvdt Hall Effect and Tranducer

Question 5

(a) Rotary variable differential transformer (RVDT)

Construction

RDVT has basic architecture design as LVDT where the ferrite core is replaced by cardiode shaped core. As in picture above, the rotary ferromagnetic core is mounted on a solid plunger which has a rotating motion. This motion will create imbalance in the circuitry and the result signal from the imbalance will be use to measure the angular displacement of the shaft.

Operation

RDVT function as measuring tool for rotational/angular angles or displacement. Examples applications are in quarter turn valve, mail sorters, and fractional shaft measurements or in actuator position sensing in the aircraft.

Advantages of RVDT

1. Low cost as due to the popularity of application.

2. Solid and Robust construction makes it to work in different environments.

3. No frictional resistance, so high accuracy over long time duration.

4. Negligible hysteresis.

5. No permanent damage to RDVT if measurement out of range.

Disadvantages of RVDT

1. Contact between plunger and measuring surface is always not possible.

2. RVDT provide linear output for about +-40 degree which limits its usability.

(b) Hall effect transducers

Construction

when no magnetic field is applied to the current carrying thin semiconductor material (hall element) the hall voltage (Vh) is zero. When an external magnetic field is applied to the current carrying hall element perpendicular to the current flow a Lorentz force acts on the current due to which a voltage called hall voltage(Vh) is generated perpendicular to both the current and the magnetic field. This voltage is very small (in uV) and needs amplification.

Operation

When current is passed through the conductor and the same conductor is placed in magnetic field perpendicular to the current flow then a voltage called the hall voltage is generated perpendicular to both the current and magnetic field. This is known as Hall Effect. Some of the applications of Hall Effect sensors are current sensing, Power sensing, Proximity detection and Speed detection

The advantages of Hall Effect sensors

* Non contact operation