Transducers

Dr. Zulfatman, M.Eng.Dept. of Electrical Engineering

Faculty of EngineeringUniversity of Muhammadiyah Malang

Lecture 2

Renungan Hari Ini

Hadiah terpenting dan terindah dari orangtua pada anak-anaknya adalah tantangan. (Psikolog Stanford University, Carol Dweck dalam Buku The New Psychology of Success)

Transducer versus Sensor

Transducer is a device that transfers energy from one system to another in the same or in the different form, for example, a microphone (input device) converts sound waves into electrical signals for the amplifier to amplify (a process), and a loudspeaker (output device) converts these electrical signals back into sound wavesSensor is a device that detects a change in a physical stimulus and turns it into a signal which can be measured or recorded, for example heat or force and covert that into an electrical signal.A sensible distinction is to use sensor for the sensing element itself and transducer for the sensing element plus any associated circuitry.

All transducers would thus contain a sensor and most (though not all) sensors would also be transducers.

Types of TransducerBased on Quantity to be Measured:■ Temperature Transducers (e.g. thermocouple)■ Pressure Transducers (e.g. diaphragm)■ Displacement Transducers (e.g. LVDT)■ Flow Transducers

Based on the Principle of Operation:■ Photovoltaic (e.g. solar cell)■ Piezoelectric■ Chemical■ Mutual Induction■ Electromagnetic■ Hall effect■ Photoconductors

Types of TransducerBased on the need for external power source:■ Active Transducers, e.g. thermocouple

No need external power source for their operation.■ Passive Transducers, e.g. photocell (LDR)

Require an external power source to produce output signal in the form of resistance, capacitance or any others electrical parameters, which than has to be converted to an equivalent current or voltage.

Commonly Used Electrical Transducers

Potentiometers, they convert the change in displacement into change in the resistance, which can be measured easily.

Rotary Potentiometer Linear Potentiometer for short-stroke displacement measurement

Commonly Used Electrical Transducers

Wheatstone Bridge, a simple circuit for measuring an unknown resistance by connecting it so as to form a quadrilateral with three known resistances and applying a voltage between a pair of opposite corners. Its operation is similar to the original potentiometer.

Commonly Used Electrical Transducers

Strain Gauge, a passive transducer that converts a mechanical elongation or displacement produced due to a force into its corresponding change in resistance R, inductance L, or capacitance C. A strain gauge is basically used to measure the strain in a work piece. When strain gauges are strained or stretched there is change in their resistance

Commonly Used Electrical Transducers

Resistive Transducer, change in the resistance of these sensors when certain physical quantity is applied to it. It is most commonly used in resistance thermometers for measurement of temperature.

The main principle of operation of an RTD and Thermistor is that when the temperature of an object increases or decreases, the resistance also increases or decreases proportionally. The sensing element used in a RTD is a metal and in a thermistor is ceramic.

Commonly Used Electrical Transducers

Capacitive transducer, comprises of two parallel metal plates that are separated by the material such as air, which is called as the dielectric material. In the typical capacitor the distance between the two plates is fixed, but in variable capacitance transducers the distance between the two plates is variable.

Capacitance decreases when the moving tube is moving out.

Commonly Used Electrical Transducers

Inductive transducer, The inductive transducers work on the principle of the magnetic induction of magnetic material. In the inductive transducers the magnetic materials are used in the flux path and there are one or more air gaps. The change in the air gap also results in change in the inductance of the circuit.

Commonly Used Electrical Transducers

Piezoelectric transducer, are a type of electroacoustic transducer that convert the electrical charges produced by some forms of solid materials into energy. When force is applied to these transducers, they produce voltage that can be measured easily. They are used for measurement of pressure, acceleration and force.

They are commonly used in residential products like motion and object detectors, pest deterrents and home security alarms.

Commonly Used Electrical Transducers

Piezoelectric Applications

Other examples:■ Air bag sensor■ Seat bell buzzers■ Sonar■ Fuel atomizer

Commonly Used Electrical Transducers

Linear Variable Differential Transformer (LVDT), LVDT is the transformer consisting of the primary and the secondary coil. It converts the displacement into the change in resistance.

Commonly Used Electrical Transducers

LVDT Applications

Commonly Used Electrical Transducers

Ultrasonic Transducer, These transducers use the ultrasonic or ultrasound waves to measure parameters like fluid level, flow rate etc.

Commonly Used Electrical Transducers

Ultrasonic Transducer Applications

Most Common Transducers in Industries

■ Linear Position Transducers■ Pressure Transducers■ Flow Measurement Transducers■ Ultrasonic Transducers■ Piezoelectric Transducers