Electronic Sensors and Measurement Techniques

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Questions and Answers

What principle do all inductive sensors operate on?

Mechanical principles

Transformer principles (correct)

Capacitance principles

Electrostatic principles

Which phenomenon does the inductance of a coil rely on?

Electromagnetic interference

Thermal conductivity

Static electricity

Distance and materials (correct)

What does a movable core in a linear variable inductance sensor do?

Increases reluctance of the magnetic path

Changes the inductance of the coil (correct)

Alters the capacitance in the circuit

Decreases the current flow in the coil

What does LVDT stand for?

Linear Variable Differential Transformer Signup and view all the answers

What is the main use of an LVDT sensor?

To measure force in terms of displacement Signup and view all the answers

Which of the following describes the output of an LVDT when the core is centered?

It generates zero output Signup and view all the answers

What type of transformer is an LVDT classified as?

Variable reluctance transformer Signup and view all the answers

How does the output of an LVDT change when the core moves to either side?

It changes in different directions (polarity) Signup and view all the answers

Which polymer is commonly used in piezoelectric sensors?

Polyvinylidene fluoride (PVDF) Signup and view all the answers

What occurs when the upper film of a PVDF sensor is deformed?

The amplitude or phase of the output signal changes. Signup and view all the answers

In the capacitance formula for a parallel plate capacitor, what does 'd' represent?

Distance between the two plates Signup and view all the answers

What can cause a variation in capacitance in capacitance transducers?

Changing the dielectric constant Signup and view all the answers

How does a capacitive pressure sensor detect pressure changes?

Through a change in capacitance due to diaphragm movement Signup and view all the answers

What does a difference in pressure (P1 & P2) cause in a capacitive sensor?

It causes the diaphragm to move toward the low-pressure side. Signup and view all the answers

Which type of sensors use changes in magnetic fields to detect position or speed?

Inductive sensors Signup and view all the answers

Which of the following materials does NOT exhibit piezoelectric properties?

Copper Signup and view all the answers

What is the primary principle behind strain gauges?

Change in resistance due to mechanical deformation Signup and view all the answers

Which equation relates force to the displacement of a spring?

F = kx Signup and view all the answers

Which aspect of piezoelectricity is true based on its definition?

It generates charge when squeezed or pressed Signup and view all the answers

What is a characteristic of tactile piezoelectric sensors?

They can generate electric voltage under strain Signup and view all the answers

The piezoelectric effect was first proven by which pair of scientists?

Pierre and Jacques Curie Signup and view all the answers

How is the output of a force sensor typically calibrated?

In units of force Signup and view all the answers

What does the term 'RESISTIVITY' refer to in the context of silicon and strain gauges?

A measure of how much a material opposes the flow of electric current Signup and view all the answers

Which method is NOT a direct measurement of force?

Measuring electrical resistance changes Signup and view all the answers

What happens to the electrical connection of a tilt sensor when it is tilted?

The current cannot flow between the terminals. Signup and view all the answers

In which position is the switch of a tilt sensor closed?

When positioned upright. Signup and view all the answers

How does an electrolytic tilt sensor measure the angle of tilt?

By changing the resistance in a fluid. Signup and view all the answers

What condition exists when the tilt sensor is in a balanced position?

Resistance between the center and outside electrodes is equal. Signup and view all the answers

Which units can the angle measured by an electrolytic tilt sensor be expressed in?

Degrees, arc minutes, and arc seconds. Signup and view all the answers

What is the primary principle that allows accelerometers to measure acceleration?

The force acting on a mass as described by Newton's second law Signup and view all the answers

In a strain gauge accelerometer, what is primarily measured to ascertain acceleration?

The bending of a cantilever beam Signup and view all the answers

Which type of accelerometer uses inductance to determine the position of the mass?

Variable inductance accelerometer Signup and view all the answers

How does a capacitive accelerometer measure acceleration?

By altering the capacitance between moving plates Signup and view all the answers

What is the main function of tilt sensors?

To detect orientation or inclination Signup and view all the answers

What component in tilt sensors aids in measuring angular movement?

A rolling ball Signup and view all the answers

Which equation represents the dynamic behavior of a mass in accelerometers?

$ma = -kx + b\frac{dx}{dt}$ Signup and view all the answers

What is the purpose of damping mechanisms in accelerometers?

To minimize oscillations of springs or beams Signup and view all the answers

Study Notes

Typical Electronic Sensor System

Input signal (measurand) is detected by a sensor
Sensor data is converted from analog to digital by a microcontroller
Signal processing and communication take place
The processed data is displayed
Example: NIH “Bionic Man' with 14 sensors controlled by the brain

Resistance Change in Metal Strain Gauges

Resistance changes due to material's geometric effect
Silicon shows a large change in resistivity with stress

Force and Tactile Sensors

Strain gauges can be calibrated to measure force
Force can also be measured by:
- Measuring the acceleration of a mass (F=ma)
- Measuring the displacement of a spring under force (F=kx)
- Measuring the pressure produced by force
These methods are not direct measures of force

Piezoelectric Sensor

Pierre and Jacques Curie discovered Piezoelectricity in 1880
Piezoelectric effect was first used by manufacturers in the 1950s
"Piezoelectricity" comes from the Greek word "pizo" meaning "to squeeze"
Piezoelectric materials generate charge when squeezed
Signal amplitude and frequency are directly proportional to material deformation

Tactile Piezoelectric Sensors

Piezoelectric materials generate voltage when strained
Strain gauge is sensitive and reliable for accurate measurement
Polymers like polyvinylidene fluoride (PVDF) are suitable for tactile sensors
Quartz, ceramics, and polymers exhibit piezoelectric properties
PVDF film is deformed by mechanical pressure

Capacitive Sensing

Capacitance of parallel plate capacitor is: C=  r 0 A/d
- A: overlapping area of plates
- d: distance between plates
-  0: permittivity of free space
-  r: dielectric constant
The varying capacitance can be used as a sensor by:
- Changing the distance between the plates
- Changing the overlapping area of the plates
- Changing the dielectric constant

Capacitance Transducers

Capacitance changes with pressure
A thin diaphragm moves towards lower pressure
The change in capacitance is proportional to pressure
This is used in pressure sensors

Inductive Sensors

Inductive sensors measure position and speed with different shapes and sizes
They work using transformer principles and alternating electrical currents
Relates to the principles observed by Michael Faraday

Inductive Sensors - Basic Phenomena

Inductance changes due to various effects including:
- Distance
- Materials
- Dimensions
Inductance is the magnetic property of a device
It responds to almost any physical property

Movable Core Sensors

Movable core changes inductance of the coil
The further the core moves in, the higher the inductance
Linear Variable Inductance Sensor (LVDT) is used for linear motion
LVDT is based on transformer principles
It measures displacement, force, pressure, and other properties

LVDT - Linear Variable Differential Transformer

LVDT is based on couplings between two coils
One primary coil and two secondary coils connected in opposition
It is a passive transducer measuring force through displacement
It operates on electromagnetic induction principles
Motion in either direction changes the output

Accelerometer

Sensor measures acceleration by measuring force on a mass
At rest, acceleration and force on mass are zero
Force on mass is proportional to acceleration with fixed mass

Accelerometers - Principles

Newton's second law: ma = -kx - bdx/dt
- m: mass
- k: spring constant
- b: damping coefficient
- x: distance
- a: acceleration
Measurement of x indicates acceleration

Strain Gauge Accelerometer

Mass is suspended on a cantilever beam
Strain gauge measures bending of the beam

Variable Inductance Accelerometer

Rod connected to mass links to coil
Inductance of coil is proportional to mass position
LVDT may be used

Capacitive Accelerometer

Fixed plate is connected to sensor body
Second plate serves as inertial mass and is connected to a restoring spring
Acceleration changes capacitance
Damping prevents oscillations

Tilt Sensors

They produce an electrical signal that varies with angular movement
They detect orientation and inclination
They measure slope and tilt within a limited range of motion

Tilt Sensor Working Principle

Consists of a rolling ball and a conductive plate
When power is applied, the ball falls to the bottom creating an electrical connection
Tilting prevents the ball from reaching the bottom, interrupting the circuit
The current flow between two terminals is interrupted

Testing a Tilt Sensor

Switch is open loop (no continuity) when pointing down
Switch is closed (low resistance/continuity) when pointing up

Electrolytic Tilt Sensors

They measure angle relative to gravity
They are non-signal conditioned sensing elements
The angle is expressed in degrees, arc minutes and arc seconds

Structure and Operation

They function like a liquid potentiometer
Conductive fluid creates variable resistance between electrodes
When balanced, the resistances to each outside electrode are equal

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Description

Explore the fascinating world of electronic sensor systems, including how input signals are converted and processed. Learn about different types of sensors such as strain gauges and piezoelectric devices, and discover their applications in measuring force and displacement. This quiz will deepen your understanding of sensor technologies and their practical uses.