Transducers/Sensors Transducer/sensor converts a non- electrical quantity, measurand, into a related electrical output signal Ideally there is a linear relationship between the measurand and the output Sensors often need a source of energisation, a power supply

Transducers/Sensors What’s the measurement made for? –Information, to quantify the measurand –Record, to provide a historical profile –Control, use the information to control some process Sensor measurements are subject to errors –Noise –cross sensitivity, output changes because it’s sensitive to other environmental variables –Characteristic errors, deviation from the predicted response –Dynamic errors, non-ideal frequency or time response

Transducers/Sensors Important Characteristics –Accuracy, usually expressed in %, variation from the stated linear (or other relationship) between measurand and output –Resolution, smallest change in the measurand that can be detected in the output –Range, range of value of the measurand that the sensor can accurately sense

Transducers/Sensors For any form of measurand there are always several sensors that can be used, which one depends on the application Similarly, many sensors can be used to sense different measurands E.g: Temperature: thermocouple, resistance thermometer, thermistor, semiconductor sensor, infra-red thermometer…… E.g: Strain gauge: strain, pressure, height, displacement, velocity, acceleration

Transducers/Sensors Sensors generate analogue outputs such as voltage or frequency Sensors generate digital outputs such as pulses or digital data

Transducers/Sensors: Examples Linear displacement: –Resistance –Capacitance –Electromagnetism LVDT (linear variable displacement transformer) –Ultrasonic –Optical –…………

Transducers/Sensors: Examples Temperature: –Thermocouple –Platinum resistance –Thermistor –Semiconductor junction –Semiconductor thermometer

Transducers/Sensors: Exercise Use the rest of the lecture time for a web search on the transducer type given: 1. Range of types available & typical devices (diagrams, photos?) 2. Accuracy, range, resolution 3. Measurand/output law (linear?, shown as a graph?, other?) 4. Cross-sensitivity? Other important electrical characteristics 5. ???