Mechanical SensorAnd Its Application

Central University Of Jharkhand

By farzi faraz

What is sensor ?

A sensor is a converter that measures a physical quantity and converts it into a signal which can be read by an observer or by an instrument.

Example a mercury in glass thermometer.

Three terms

Transducer a device that converts a primary form of energy into a

corresponding signal with a different energy forms.

Sensor a device that detect or measures a signal.

Actuator a device that generates a signal.

realworld actuator

sensor intelligentfeedbacksystem

Mechanical Sensor

Class of sensors to measure mechanical phenomena.

Includes

Pressure sensor

Force and torque sensor

Inertial sensor

Flow sensor

Mechanical Sensing Techniques

Piezoresistivity Piezoelectricity Capacitive techniques Inductive techniques Resonant techniques

Piezoresistivity Effect exhibited by various materials that exhibit a change in

resistance due to an applied pressure.

Strain Gauge

Sensors that exhibit a change in resistance as a result of an applied strain are generally termed strain gauges.

The strain gauge (SG) is glued to the element whose strain is to be measured

When stress is applied, the element and the SG is deformed at the same manner

Gauge factor is defined as

Indicates how easy the strain can be measured

Large GF means large change in resistance for a given strain

/

strain

R RGF

Strain gauge

Piezoelectricity

the property of producing an electric charge when subjected to an applied mechanical force.

Effect arises because of the charge asymmetry within the crystal structure.

Quartz and Rochelle salt are naturally occurring piezoelectric.

Applied force

Piezoelectric material

Capacitive Techniques

The displacement measurement due to the change in capacitance.

Capacitance

There are 3 ways to change capacity

variation of plate separation

variation of plate area

variation of dielectric constant

0

AC K

d

Inductive Techniques

Inductance a motion of permeable core changes the inductance

AC bridge can be used to detect the change in inductance

sB dS

Li

A resonator is a mechanical structure designed to vibrate at a particular resonant frequency.

Resonant Techniques

Block Diagram

Pressure Sensor Pressure sensor is use to measure the pressure of fluid and

gas in industrial application.

Pressure is force per area that fluid exerts on its surroundings

Static Pressure

The fluid is not moving

Dynamic Pressure

The fluid is moving

Principles Involves Are

ghPP 12

2 21 1 1 2 2 2

1 1

2 2P v gy P v gy =constant

Pressure sensor Pressure sensor types Absolute pressure sensor

sensor measures the pressure relative to perfect vacuum.

Gauge pressure sensor

sensor measures the pressure relative to atmospheric pressure.

Vacuum pressure sensor

sensor that measures pressures below atmospheric pressure.

Differential pressure sensor

sensor measures the difference between two pressures

Force and torque sensor The fundamental operating principles of force and torque sensor

instrumentation are closely allied to the piezoelectric and strain gage devices used to measure static and dynamic pressures.

Consider a simple sensor that is to be developed to measure a reaction force at the base of a spring, as shown below.

Force and torque sensor Torque is a measure of the forces that causes an object to

rotate.

Reaction torque sensors measure static torque with a stationary or non-rotating transducer.

Rotary torque sensors use rotary transducers to measure torque.

Inertial Sensor Inertial sensor measures linear acceleration along

one or several axis refered to as accelerometer. Sensor that measures angular acceleration along

one or several axis are refered to as gyroscope.

accelerometergyroscope

Flow Sensor A flow sensor is a device for sensing the rate of flow

of material. Material may be solid liquid or gas. Flow rate is measured by weighting the amount of

material on a platform of length L

flow (kg/min or lb/min)

weight of material on section of length L (kg or lb)

conveyor speed (m/min, or ft/min)

length of weighting platform

Q

W

R

L

WRQ

L

Application of different mechanical sensor

Central University of Jharkhand

Application OF Pressure Sensor Manometer a traditional pressure sensor.

Manometers can be used both as a gauge sensor with one side

vented to atmosphere and as differential sensors with pressure

applied to both legs.

Pressure sensor are also use in aneroid barometer and

bourdon tube.

Microphones are a particular type of MEMS pressure

sensor designed to transduce acoustic signals into

electrical output. example hearing aid

U tube manometerBourdon tube

Pressure sensor application in auto parts

sensor Auto parts applications

Application of force and torque sensor A force-sensing resistor is a material whose resistance

changes when a force or pressure is applied. They are also known as forcesensitive resistor.

Torquemeter is a device for measuring and recording the torque on a rotating system, such as an engine, crankshaft, gearbox etc

In control systems when motion feedback is employed. In process testing, monitoring and diagnostics

applications. In measurement of power transmitted through a rotating

device.

In controlling complex non-linear mechanical systems.

torquemeter

Force sensitive resister

Application of inertial sensor Accelerometer

In industrial application, the design of accelerometer is

based on Newton’s Law and Hooke’s Law of Spring

Inertial sensors are used for military applications such as inertial guidance and smart ammunition.

Accelerometers can be used to measure vibration on cars, machines, buildings, process control systems and safety installations.

ma k x

2

spring constant in N/m

spring extension in m

mass in kg

acceleration in m/s

k

x

m

a

accelerometer

Application of flow sensor flow sensors are based on sensors which measure the transfer

of heat caused by the moving medium. This principle is common for microsensors to measure flow.

Velocimetry Velocimetry is the measurement of the velocity of fluids.

For measuring velocity and length on moving surfaces, laser surface velocimeters are used.

velocimeter

THANK YOU