Jawaharlal Nehru Technological University Hyderabad B.Tech II TRANSDUCERS ENGINEERING Previous Question Paper (August/September - 2022 - R18)

A generalized measurement system consists of several functional blocks that process the input signal to provide a usable output. The block diagram follows the sequence: Primary Sensing Element → Variable Conversion Element → Variable Manipulation Element → Data Transmission Element → Data Presentation Element.

1. Primary Sensing Element: Detects the physical quantity (measurand) and converts it into a usable electrical or mechanical signal.

2. Variable Conversion Element: Converts the output of the primary sensing element into a more suitable variable, typically an electrical signal, without changing the information content.

3. Variable Manipulation Element: Manipulates the signal (e.g., amplification, filtering, or attenuation) to make it compatible with the next stage.

4. Data Transmission Element: Transmits the signal from one location to another, often over long distances, using cables, wireless links, or telemetry.

5. Data Presentation Element: The final stage that provides the information in a readable format, such as a digital display, recorder, or computer interface.

The Linear Variable Differential Transformer (LVDT) is an electromechanical transducer that converts linear displacement into a proportional electrical voltage.

Construction: It consists of a primary winding and two identical secondary windings (S1 and S2) wound on a hollow cylindrical former. A high-permeability, movable soft iron core is placed inside the former, connected to the object whose displacement is to be measured.

Principle of Operation: An AC excitation voltage is applied to the primary winding. The magnetic flux produced links with the secondary windings. The output voltage is the difference between the voltages induced in the two secondary windings (V_out = V_s1 - V_s2).

Characteristics:

• At the null position (center), the core links equal flux to both secondaries, resulting in zero output voltage.
• When the core moves, the flux linkage becomes unequal, producing an output voltage proportional to the displacement.
• The output is linear over a specific range of displacement.
• It offers high sensitivity, infinite resolution, and low friction due to the absence of physical contact between the core and coils.
• It provides high output voltage for small displacements and excellent repeatability.