JAWAHARLAL NEHRU TECHNOLOGICAL UNIVERSITY HYDERABAD B.Tech IV SENSORS AND TRANSDUCERS Previous Question Paper (July - 2021 - R16)

Measurement errors are defined as the difference between the measured value and the true value of a quantity. These errors are broadly categorized into three types based on their origin and nature.

1. Gross Errors: These are primarily caused by human mistakes in reading, recording, or calculating data. Examples include incorrect instrument adjustment, misreading a scale, or improper application of an instrument. These errors cannot be treated mathematically but can be minimized by taking multiple readings, ensuring careful observation, and using automated measurement systems.

2. Systematic Errors: These errors occur due to shortcomings in the instrument or the measurement environment and consistently affect the measurement in one direction. They are further classified as:

• Instrumental Errors: Caused by inherent defects in the instrument, such as friction in bearings, weak springs, or improper calibration.
• Environmental Errors: Result from external conditions like temperature, pressure, humidity, or magnetic fields affecting the sensor performance.
• Observational Errors: Caused by parallax during reading or incorrect mounting of the instrument.

Systematic errors can be corrected by proper calibration, applying correction factors, or redesigning the measurement setup.

3. Random Errors: These are unpredictable variations that remain after systematic and gross errors have been accounted for. They arise from unknown, small, and rapidly changing disturbances in the measurement system or environment, such as electronic noise or slight fluctuations in power supply. Because they are random, they cannot be eliminated but can be analyzed using statistical methods. By taking a large number of readings, the mean value can be calculated, and the precision can be determined using standard deviation and probability distribution functions to estimate the most probable value.

A transducer is an electronic device that converts energy from one form into another. Typically, it converts a non-electrical physical quantity (such as temperature, pressure, displacement, or light) into an electrical signal (such as voltage, current, or resistance change), or vice versa. The process involves two main components: a sensing element that detects the physical change and a transduction element that converts the detected change into an electrical output.

Transducers are broadly classified based on the following criteria:

1. Based on the Power Source:
   • Active Transducers: These do not require an external power source to operate. They generate their own electrical output through the energy conversion process, such as piezoelectric crystals, thermocouples, and photovoltaic cells.
   • Passive Transducers: These require an external power supply to produce an output signal. They function by changing their electrical parameters like resistance, capacitance, or inductance, such as LVDT, strain gauges, and thermistors.
2. Based on the Transduction Principle:
   • Resistive: The physical quantity changes the resistance of the element (e.g., Potentiometer, RTD).
   • Capacitive: The physical quantity changes the capacitance (e.g., Capacitive pressure sensor).
   • Inductive: The physical quantity changes the self or mutual inductance (e.g., LVDT).
   • Photoelectric: The physical quantity changes light intensity into electrical energy (e.g., LDR, Photodiode).
3. Based on the Nature of Output:
   • Analog Transducers: These provide a continuous output signal that is a function of the input, such as a strain gauge outputting a varying voltage.
   • Digital Transducers: These convert the input into a discrete or digital format, such as shaft encoders or digital pressure sensors.
4. Based on the Direction of Energy Flow:
   • Primary Transducers: These are the first elements that detect the physical quantity and convert it into a mechanical or other non-electrical form.
   • Secondary Transducers: These take the output of the primary transducer and convert it into an electrical signal.