INTRODUCTION TOMEASUREMENT SYSTEMS & DEVICES

Module-3

MODULE OBJECTIVES Upon successful completion of this module, students should

be able to:

Define a measurement system and identify its main elements Explain the role of sensors/transducers in a measurement

system Define the terms sensitivity and linearity of a

sensor/transducer Identify different sensors used in temperature measurements Determine the sensor characteristics through experiments Understand and perform calibration of temperature sensor/transducer.

INTRODUCTION TO MEASUREMENT SYSTEMS

We use the term ‘measurements’ everyday in our lives Noting the time on our watch/clock Recording the temperature Tracing the speed of a car Estimating electricity consumption, and so on

INSTRUMENTSAn instrument is a device used to

measure a physical variable. A ruler, for example, provides measurement of length

temperature, distance, pressure, force, humidity

PROCESS A process is a sequence of operations

carried out to achieve a desired result.

For example, fixing a flat tire is a process. Similarly, maintaining the temperature of a

room within the desired limit is a process.

Manual

Automatic

MEASUREMENT SYSTEM ELEMENTS Any Measurement system consists of

three basic parts: transducer/sensor signal processor and recorder

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SENSOR A sensor is a device that senses a

physical variable, such as temperature, force, or pressure etc

TRANSDUCER A transducer is a device that converts a

physical quantity into a measurable quantity, usually an electrical signal

MEASUREMENT SYSTEM EXAMPLE Temperature measurement system

DEFINITION Transducer – Thermocouple is the

transducer that converts the input temperature to a small voltage (in millivolt).

Signal processor –The signal processor increases the level of the voltage and converts it to a digital format.

Recorder- LED display displays the temperature in digits.

TASK-1 : GO TO QUIA & ANSWER THE QUESTION

LINEARITY Some transducers output a signal that is

proportional to the input physicalquantity. These transducers are called linear devices.

Other transducers that don’t have a proportional relationship between the output signal and the input are non-linear devices.

SENSITIVITY Sensitivity is the ratio of change in the

output signal to the change in the amount of the physical parameter being measured.

Sensitivity = Change in Output / Change in Input

CALIBRATION Calibration is the comparison of

measurement with a standard

CALIBRATION Calibration is done by: Measuring the transducer output for

known physical quantities Determining the best mathematical

relation between the input and the output

TEMPERATURE MEASUREMENT Temperature is the degree of hotness or

coldness measured on a definite scale. The various units for measuring

temperature are celsius, kelvin and fahrenheit.

The SI unit of temperature measurement is the ‘kelvin’.

TEMPERATURE MEASUREMENT Temperature can be measured using

any one of the following methods depending on the application: Immersion in a gas or liquid Surface Contact with the solid No contact

Measuring device: thermometer, thermistor and thermocouple

THERMOMETER Mercury thermometer is a temperature

sensor that converts the measured temperature into expansion and contraction of a liquid which can be read on a calibrated glass tube.

THERMOCOUPLE Thermocouple is a temperature

transducer that consists of two different metals, joined together at one end

THERMISTOR The thermistor is a thermally sensitive

resistor, the resistance of which varies with temperature.

TASK-2 Identify the input physical quantity and the output for the

sensors given in the table.

LAB ACTIVITY 1