Transducer• Transducer – A transducer is a device that converts one type of energy to another. – a device that converts a primary form of energy into a corresponding signal with a different energy form • Primary Energy Forms: mechanical, thermal, electromagnetic, optical, chemical, etc. – take form of a sensor or an actuator.• Sensor (e.g., thermometer) – a device that detects/measures a signal or stimulus – acquires information from the “real world”• Actuator (e.g., heater) – a device that generates a signal or stimulus
Found in Day to Day Life– Many people think of a transducer as being some sort of technical device, but they can be found in many places in day to day life.– A microphone, for example, converts sound waves that strike its diaphragm into an analogous electrical signal that can be transmitted over wires.– Most transducers have an inverse that allows for the energy to be returned to its original form. Audio cassettes, for example, are created by using a transducer to turn the electrical signal from the microphone pick-up — which went through a transducer to convert the sound waves into an electrical signal — into magnetic fluctuations on the tape head.
• Other transducers turn one type of energy into another form, not to measure something in the external environment or to communicate information, but rather to make use of that energy in a more productive manner.• A light bulb, for example, converts electrical energy into visible light. Electric motors are another common form of electromechanical transducer, converting electrical energy into kinetic energy to perform a mechanical task.• The inverse of an electric motor — a generator — also is a transducer, turning kinetic energy into electrical energy that can then be used by other devices.
Efficiency of transducers• As in all energy conversions, some energy is lost when transducers operate. The efficiency of a transducer is found by comparing the total energy put into it to the total energy coming out of the system. Some transducers are very efficient, and others are extraordinarily inefficient.• A radio antenna is one example of an efficient transducer. The antenna acts as a transducer to turn radio frequency power into an electromagnetic field. When the antenna is operating well, this process can be more than 80% efficient.• Most electrical motors, by contrast, are less than 50% efficient. A common light bulb, because of the amount of energy that is lost as heat, is less than 10% efficient .
What are Electrical Transducers?• The transducers that convert the mechanical input signals of the physical quantity into electrical output signals are called as electrical transducers.• The input given to the electrical transducers can be in the form of the displacement, strain, velocity, temperature, flow etc and the output obtained from them can be in the form of current, voltage and change in resistance, inductance and capacitance.• The output can be measured easily and it is calibrated against the input, thus enabling the measurement of the value of the input.
Example of Electrical Transducers• Potentiometers: They convert the change in displacement into change in the resistance, which can be measured easily.• Bridge circuits: These convert the physical quantity to be measured into the voltage.• Wheatstone bridge: It converts the displacement produced by the physical quantity to the current in the circuit.• Variable Capacitance Transducers: These comprise of the two parallel plates between which there is dielectric material like air. The change in distance between the two plates produced by the displacement results in change in capacitance, which can be easily measured
• Variable Resistance Transducers : There is change in the resistance of these sensors when certain physical quantity is applied to it. It is most commonly used in resistance thermometers or thermistors for measurement of temperature.• Magnetic sensors: The input given to these sensors is in the form of displacement and the output obtained is in the form of change in inductance or reluctance and production of the eddy currents.• Piezoelectric transducers: 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
• Strain gauges: When strain gauges are strained or stretched there is change in their resistance. They consist of the long wire and are able to detect very small displacements produced by the applied force or pressure.• Photo electric transducers: When the light is applied to these transducers they produce voltage.• 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.• Ultrasonic Transducers: These transducers use the ultrasonic or ultrasound waves to measure parameters like fluid level, flow rate etc.
Circuits of some Electrical Transducer• Thermistor Circuit A Thermistor is a temperature dependent resistor. When temperature changes,the resistance of the thermistor changes in a predictable way. when you refer to this thermistor ,you would say it has 5kW at room temperature. Resistance of thermistor at T (oC) R (ohm) Resistance of themistor at 0 16330 different temp. is as shown 25 5000 in the table. 50 1801
Operational Amplifiers properties • open-loop gain: ideally infinite: practical values 20k-200k –high open-loop gain virtual short between + and - inputs • input impedance: ideally infinite: CMOS opamps are close to ideal • output impedance: ideally zero: practical values 20-100 • zero output offset: ideally zero: practical value <1mV • gain-bandwidth product (GB): practical values ~MHz –frequency where open-loop gain drops to 1 V/V• Commercial opamps provide many different properties – low noise – low input current – low power – high bandwidth – low/high supply voltage – special purpose: comparator, instrumentation amplifier
Basic Opamp Configuration• Voltage Comparator - digitize input• Voltage Follower – buffer• Non-Inverting Amp • Inverting Amp