RVDT – Rotary Variable Differential Transformer Explained

In the previous article, we have discussed an overview of LVDT or Linear Variable Differential Transformer. This article discusses an overview of RVDT, and the RVDT full form is Rotary Variable Differential Transformer. The designing of RVDT is same like an LVDT, apart from the design of core. Because, when it turns then the mutual inductance among the two windings of the transformer namely the primary coil and the secondary coils will change linearly by the angular displacement. RVDT’s uses brushless, non-contacting equipment for ensuring long-life, consistent, repeatable and position detecting by unlimited resolution. Such performance guarantees precise position sensing under the most intense working conditions.

What is RVDT (Rotary Variable Differential Transformer)?

The RVDT stands for Rotary Variable Differential Transformer. It is one kind of electromechanical transducer used to give the linear o/p which is proportional to the i/p angular displacement. The main function of RVDT is to detect the angular displacement and converts it into an electrical signal. The both the RVDT and LVDT workings are similar, but LVDT employs the flexible iron core for displacement measurement whereas in RVDT employs a cam type core. This core will turn among the two windings of the transformer using the shaft. Please refer the link to know more about LVDT: Construction, working principle, advantages, disadvantages, and its applications.

Rotary Variable Differential Transformer
Rotary Variable Differential Transformer

RVDT Construction and Its Working

RVDT transducer has two windings similar to a normal transformer such as primary winding and two secondary windings shown in the following RVDT diagram. The two windings of the transformer wounded, where the two secondary windings have an equivalent number of windings. These are located on both sides of the primary winding of the transformer. A cam formed a magnetic core which is made with a soft iron is coupled to a shaft. Thus, this core can be twisted among the windings. The construction of both the RVDT and LVDT are similar but the main difference is the shape of the core in transformer windings. This core will turn between the two windings of the transformer due to the shaft.

RVDT Construction
RVDT Construction

The typical RVDTs are linear over a +40 or -40 degrees, Sensitivity is about 2mV to 3mV per degree of rotation and the input voltage range is 3V RMS at frequency ranges from 400Hz to 20kHz. Based on the movement of the shaft in the transformer, the three conditions will be produced such as

  • When the Core is at Null Position
  • When the Core Rotates in Clockwise Direction
  • When the Core Rotates in Anticlockwise Direction

When the Core is at Null Position

In the first condition, when the shaft is placed at the null position then the induced e.m.f in the secondary windings are similar although reverse in phase. Thus, the differential o/p potential will be zero, and the condition will be E1 = E2, where E0 = E1-E2 =0

When the Core Rotates in Clockwise Direction

In the second condition, when the shaft rotates in the direction of clockwise; more section of the core will enter across the primary winding. Therefore, the induced e.m.f across the primary winding is higher than secondary winding. Hence, the differential o/p potential is positive, and the condition will be E1 > E2, where E0 = E1-E2 = positive.

When the Core Rotates in Anticlockwise Direction

In the third condition, when the shaft rotates in the direction of anticlockwise, more section of the core will be entered across the secondary winding. Thus, the induced e.m.f across the secondary coil is higher than the primary coil. Hence, the differential o/p potential is negative that means 1800 phase shift, and the condition will be E1 < E2, where E0 = E1-E2 = negative.

How to Choose RVDT?

The RVDTs have many advantages over other types of sensors. But, there are some parameters to be considered in selecting the RVDT which include the following.

Accuracy

In some situations, RVDT accuracy is imperfect due to this reason it is not appropriate for some of the application. Whenever the appliance needs high-accuracy sensors then the cost of the appliance will also be enhanced.

Work Environment

RVDTs are very strong and they can work in any environment. Other types of sensors are not appropriate for the conditions like a tremendous change in temperature, the presence of pollutants, or high sounds of vibration.

Backup Power Source

An RVDT needs an input of alternating current for generating the preferred analysis output. If there is no backup power source, then an electromechanical sensor will not be a good choice.

Change of Signal

Nowadays, for some applications choose a sensor which can be used for changing the data into the readable digital output on PC.

RVDT Advantages and Disadvantages

The advantages of RVDT include the following.

  • The consistency of RVDT is high
  • The exactness of RVDT is high
  • The lifespan is long
  • The performance is repeatable
  • The construction is compact and strong
  • Durability
  • Low cost
  • Easy to handle electronic components
  • Resolution is infinite
  • Linearity is Excellent
  • A wide range of dimension ranges

The disadvantages of RVDT mainly include the following

  • The contact among the measuring exterior as well as the nozzle is not possible for all time.
  • The output of the RVDT is linear (about +40 or -40 degrees), so it restricts the usability.

RVDT Applications

The applications of RVDT include the following.

  • Fuel Valves as well as Hydraulic
  • Modern machine tools
  • Controls Cockpit
  • Controls Fuel
  • Brake with cable systems
  • Engines bleed air-systems
  • Robotics
  • Aircraft and Avionics
  • Process Control industry
  • Weapon and Torpedo Systems
  • Engine fuel control
  • Nose wheel steering systems
  • Fly by wire systems
  • Push reverser
  • Actuators for controlling Flight as well as Engine
  • Ecological control systems

Thus, this is all about RVDT (Rotary Variable Differential Transformer), construction, working, advantages, disadvantages and its applications. These are most commonly used sensors nowadays, and it doesn’t experience any functional problems because of its contactless structure. These have a fixed status for consistency even in the hard environmental conditions. So, it is an ideal sensor for constructing heavy equipment in industries like oil, gas, and aerospace. Here is a question for you, what is the RVDT working theory? You may also read more about the differences between lvdt and rvdt.

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