MR3491 SENSORS AND INSTRUMENTATION (UNIT III - FORCE, MAGNETIC AND HEADING SENSORS)

MR3491 SENSORS AND
INSTRUMENTATION
UNIT III - FORCE, MAGNETIC AND
HEADING SENSORS
Prepared by
A.R.SIVANESH
Assistant Professor
Department of Mechanical Engineering
Sri Ranganathar Institute of Engineering and Technology,
Coimbatore
Prepared by A.R.Sivanesh M.E.,(Ph.D) 1

Syllabus
Strain Gage, Load Cell, Magnetic Sensors –types, principle,
requirement and advantages: Magneto resistive – Hall
Effect – Current sensor Heading Sensors – Compass,
Gyroscope, Inclinometers
2
Prepared by A.R.Sivanesh M.E.,(Ph.D)

Strain Gage
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Load Cell
20

Load Cell
• Load cell is a sensor or a transducer that converts a load or force acting
on it into an electronic signal. This electronic signal can be a voltage
change, current change or frequency change depending on the type of
load cell and circuitry used.
There are many different kinds of load cells.
• Resistive load cells work on the principle of piezo-resistivity. When a
load/force/stress is applied to the sensor, it changes its resistance. This
change in resistance leads to a change in output voltage when a input
voltage is applied.
• Capacitive load cells work on the principle of change of capacitance
which is the ability of a system to hold a certain amount of charge
when a voltage is applied to it. For common parallel plate capacitors,
the capacitance is directly proportional to the amount of overlap of the
plates and the dielectric between the plates and inversely proportional
to the gap between the plates.
21

How does a resistive load cell works
• A load cell is made by using an elastic member (with
very highly repeatable deflection pattern) to which a
number of strain gauges are attached.
22

• In this particular load cell shown in above figure, there
are a total of four strain gauges that are bonded to the
upper and lower surfaces of the load cell.
23

• When the load is applied to the body of a resistive load
cell as shown above, the elastic member, deflects as
shown and creates a strain at those locations due to
the stress applied. As a result, two of the strain gauges
are in compression, whereas the other two are in
tension as shown in below animation.
24

• During a measurement, weight acts on the load cell’s
metal spring element and causes elastic deformation.
• This strain (positive or negative) is converted into an
electrical signal by a strain gauge (SG) installed on the
spring element. The simplest type of load cell is a
bending beam with a strain gauge.
• We use wheatstone bridge circuit to convert this
change in strain/resistance into voltage which is
proportional to the load.
25

Wheatstone Bridge Circuit
• The four strain gauges are configured in a Wheatstone
Bridge configuration with four separate resistors
connected as shown in what is called a Wheatstone
Bridge Network.
• An excitation voltage – usually 10V is applied to one set
of corners and the voltage difference is measured
between the other two corners.
• At equilibrium with no applied load, the voltage output
is zero or very close to zero when the four resistors are
closely matched in value. That is why it is referred to as
a balanced bridge circuit.
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Wheatstone Bridge Circuit
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• When the metallic member to which the strain gauges
are attached, is stressed by the application of a force,
the resulting strain – leads to a change in resistance in
one (or more) of the resistors.
• This change in resistance results in a change in output
voltage. This small change in output voltage (usually
about 20 mVolt of total change in response to full load)
can be measured and digitized after careful
amplification of the small milli-volt level signals to a
higher amplitude 0-5V or 0-10V signal.
• These load cells have been in use for many decades
now, and can provide very accurate readings but
require many tedious steps during the manufacturing
process
28

Magnetic sensor
29

Magnetic sensor
• A magnetic sensor usually refers to a sensor that converts the
magnitude and variations of a magnetic field into electric
signals.
• Magnetic fields, as exemplified by the magnetic field of the
earth (earth magnetism) or magnets are familiar yet invisible
phenomena.
• Magnetic sensors that convert invisible magnetic fields into
electric signals and into visible effects have long been the
subject of research.
• It started decades ago with sensors using the electromagnetic
induction effect and these efforts were extended to
applications of the galvanomagnetic effect, magnetoresistance
effect, Josephson effect and other physical phenomena.
30

Magnetic sensors types
a) Coils
b) Reed switches
c) MR sensor elements
d) Hall elements
e) SQUID
31

a) Coils
• The coil is the most classic and simple form of sensor,
we will discuss here.
• Although a coil cannot be used alone to directly detect
a magnetic field, it can detect the variations in a
magnetic field.
• Bringing a magnet close to a coil will increase the
magnetic flux density in the coil. The increase of
magnetic flux density in the coil will also generate
opposing forces in the form of induced electromotive
force and induced current. When the coil stops moving,
the magnetic flux density variations also stop and the
induced electromotive force and induced current
cease.
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a) Coils
33

a) Coils
• Observing the induced electromotive force and
induced current will allow you to detect the ratio of
change in magnetic flux density and its direction.
Used alone, a coil provides only limited functionality.
However, when combined with other coils or magnetic
materials, it can become a highly sensitive magnetic
sensor.
• Currently, magnetic sensors that use coils include
search coils, resolvers or rotation angle sensors as well
as fluxgate sensors, a type of sensor used in a broad
range of applications.
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b) Reed switches
• A reed switch consists of a glass tube encapsulating
two reeds, the contacts, which come from the right and
left ends of the tube.
• The reeds are made of nickel or other magnetic
material and are separated by a gap. The glass tube is
filled with nitrogen or other inert gas to prevent the
activation (deterioration) of the contacts.
• The reed switch is normally open, but when both ends
of the magnetic material are exposed to a magnetic
field, the magnetic material is magnetized and the
contacts are attracted to each other closing the circuit
(conduction state).
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b) Reed switches
36

b) Reed switches
• A reed relay, a piece of commonly used industrial
equipment, can be made by combining a coil for
generating a magnetic field with a reed switch.
• Unlike semiconductor sensors such as MR sensor
elements or Hall elements (see below), the reed switch
operates without a power supply and is therefore often
used in automobiles or other locations where power is
difficult to supply.
37

• An MR sensor element is a magnetic sensor element using the
Magneto-Resistance effect (MR effect). There are a number of
MR sensor types using different operating principles. The
following describes the basic MR effect.
• The MR effect is a phenomenon where resistance changes
with changes in a magnetic field. It is an effect that occurs in
magnetic materials (for example, iron, nickel or cobalt).
• The MR effect requires an understanding of electron spin and
how the Lorentz force operates using electron charges.
When electrons move through a ferromagnetic material (a
material with a certain level of magnetism) and the spinning of
the electrons fluctuates, the scattering probability (of
electrons) in the magnetized material rises and falls. This is
what causes the MR effect.
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• Electrons have two important parameters: charge and spin.
They have the same negative charge, but electron spin is of
two kinds: up-spin and down-spin.
• Electron spin was verified by an experiment in 1922 and it was
confirmed that electrons exhibit electronic angular
momentum and magnetic moment characteristic to electrons.
When electrons pass through conductive materials, they
scatter (electron scattering).
• Electron scattering is a phenomenon caused by static
electricity in the material that causes electrons to deviate
from their normal trajectory.
• Lorentz force is a force that comes into play when mobile
particles (electrons) in a conductive material are exposed to a
magnetic field. It affects all charged particles and does not rely
on electron spin. 39

AMR sensor elements
• In 1856, William Thomson discovered Anisotropic
Magneto-Resistance effect (AMR effect) by observing a
ferromagnetic material placed in an external magnetic
field environment.
• When the magnetization direction in a ferromagnetic
material is parallel to the current, the electron orbital
becomes perpendicular to the current, which
maximizes resistance. This increases the spin-
dependent scattering causing electric resistance to rise.
• When the magnetization direction is perpendicular to
the current, the electron orbital becomes horizontal to
the current reducing the spin-dependent scattering,
which minimizes resistance.
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AMR sensor elements
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AMR sensor elements
• The rate of change in resistance caused by the state of
the magnetic field is called magnetoresistive ratio (MR
ratio). The MR ratio for an AMR sensor element is
about 5%. The AMR sensor element is often used in
magnetic switches and rotation sensors because of its
simple structure.
42

GMR sensor elements
• The Giant Magneto-Resistive effect (GMR effect) was independently
and simultaneously discovered by Albert Fert and Peter Grünburg in
1988 by observing a non-magnetic conductive thin film structure
sandwiched between two conductive ferromagnetic material layers.
• The magnetization of each ferromagnetic layer is exposed to the spin-
dependent scattering of electrons as they pass through the middle
layer.
• If the spin direction of electrons passing through the ferromagnetic
layer is opposite that of the magnetization of the ferromagnetic
material, the interaction effect is much weaker than when the direction
of spin is parallel to magnetization.
• As a result, when the direction of magnetization of the upper and
lower ferromagnetic material is parallel, resistance to the current
flowing along the boundary surface of the conductive material drops,
while it increases if the direction of magnetization is anti-parallel.
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GMR sensor elements
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GMR sensor elements
• The GMR sensor element is a magnetic sensor element
applying the GMR effect. It has a magnetic sensitivity that is
between two to five times greater than that of an AMR sensor
element.
• This greater sensitivity allows a GMR sensor to detect minute
changes in magnetic flux densities that were previously not
possible. By replacing the coils in the read-write heads of a
hard disk drive, the heads can be made more compact and
more sensitive.
• This has vastly increased the storage densities of hard disks
increasing their storage capacities.
• The MR ratio of a GMR sensor element is about 20%.Their
high sensitivity makes GMR sensor elements the device of
choice for magnetic heads, rotational sensors and other
devices. 45

TMR sensor elements
• The Tunnel Magneto-Resistance effect (TMR effect) at
room temperature was discovered by Professor
Terunobu Miyazaki at Tohoku University in 1995.
• A TMR sensor element is a magnetic sensor element
using the TMR effect and configured from an extremely
thin nanometer level nonmagnetic insulation layer
sandwiched between two ferromagnetic layers.
• Electrons tunnel from one ferromagnetic layer into the
other via insulation layer. This is a quantum mechanical
phenomenon.
• Resistance decreases when the magnetization direction
of the two ferromagnetic materials is parallel and
increases when it is antiparallel.
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TMR sensor elements
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d) Hall elements
• The Hall element is an application of the Hall Effect.
The Hall effect discovered by Edwin H. Hall in 1879
proved that the Lorentz force generated a voltage at
right angles to the direction of the current and
magnetic field.
• This voltage is called a Hall voltage and according to
Fleming’s left hand rule the direction of the voltage
changes with the direction of magnetic flux.
• The magnitude and direction (plus, minus) of the
voltage make it possible to detect the magnitude and
direction of the magnetic field (N-pole, S-pole).
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d) Hall elements
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d) Hall elements
• The magnetic sensitivity of a Hall element is not as
good as that of magnetic resistance sensor element.
• However, as a magnetic sensor that does not rely on
magnetic material, it can be used in a ferromagnetic
field environment or harsh environments and therefore
finds application as a current sensor or as a variety of
magnetic switches.
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e) SQUID
• Superconducting Quantum Interference Device
(SQUID) is a magnetic sensor element capable of
measuring minute magnetic fields by applying the
Josephson effect.
• SQUID, a device that combines a ring-
shaped superconductor with the Josephson Junction
proposed by Brian D. Josephson in 1962 is the most
sensitive magnetic sensor currently available.
• This sensor can detect the heart’s and brain’s
electromagnetic fields, which are undetectable to
other sensor technologies.
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Hall Effect
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Hall Effect
• Hall-effect sensors are the linear transducers that are used to measure
the magnitude of the magnetic field. Working on the principle of Hall
Effect, these sensors generate a Hall voltage when a magnetic field is
detected, which is used to measure the magnetic flux density.
• Linear sensors can measure the wide range of magnetic fields. Besides
magnetic fields, these sensors are also used for detecting proximity,
position, speed. For these sensors output voltage is directly proportional
to the magnitude of the magnetic field.
• When a thin conductor (or semiconductor) has a steady flow of current
running through it and a magnet is placed so that its magnetic field runs
perpendicular to this current, the magnetic field of the current reacts to
the magnetic field of the permanent magnet, causing the electrons
flowing through the conductor to be pulled to one side of the conductor,
due to the Lorentz force. This creates a potential difference, referred to
as Hall voltage, in the conductor. The magnitude of the Hall voltage is
proportional to the strength of the magnetic field.
• The Lorentz force is the force that a particle experiences due to electrical
and magnetic fields. 53

Hall Effect
54

Hall Effect
• Hall voltage is produced when the magnetic field of a
current flowing through a conductor reacts to the
magnetic field of a permanent magnet perpendicular
to the current flow.
• The Hall effect is put to use in sensors, where the
resulting Hall voltage can indicate the presence,
absence, or strength of a magnetic field. Although Hall
sensors operate by detecting a magnetic field, they can
be used for sensing a wide variety of parameters,
including position, temperature, current, and pressure.
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Current Sensor
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Current Sensor
• A device that is used to detect & also change current to
assessable output voltage is known as a current sensor.
This output voltage is simply proportional to the
current flow throughout the measured path.
• After that, this output voltage signal is used to display
the current measured within an ammeter, for
controlling purposes or simply stored for more analysis
within a data acquisition system. So this is the function
of a current sensor.
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Current Sensor Working Principle
• The working principle of the current sensor is; once current is
supplied throughout a circuit or a wire then a voltage drop
takes place and also magnetic field will be generated nearby
the current-carrying conductor.
• So, there are two kinds of current sensing direct current
sensing & indirect current sensing.
• Direct sensing mainly depends on Ohm’s law whereas indirect
sensing depends on Ampere’s & Faraday’s law. Direct Sensing
is used to measure the voltage drop associated with the flow
of current throughout passive electrical components.
• Similarly, indirect sensing is used to measure the magnetic
field nearby a current-carrying conductor. After that, the
magnetic field which is produced is used for inducing
proportional current o voltage which is afterward changed to
use measurement or control purposes.
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Current Sensor Specifications
• Measuring Range
The measuring range is the highest flow of current that a current sensor can measure up to
120A.
• Input Voltage
This is the required voltage to activate the device is +5V.
• Frequency Range
The range of frequency this sensor can operate is 20Hz – 20kHz.
• Response Time
The response time of this sensor is the time taken between the input excitation application &
the appearance of the equivalent o/p signal. The response time of this sensor is < 20 ns.
• Isolation Voltage
The isolation voltage is the voltage that a sensor can handle to defend the devices connected to
it. If the voltage range is increased than the fixed range then it can damage the current sensor &
gives inaccurate measurements.
• Accuracy
The accuracy of the current sensor is above 90%.
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Types of Current Sensor
Shunt Resistor
• Shunt resistor type current sensor is mainly used for
measuring DC current. Once a DC current is supplied
throughout a resistor, then the voltage will be
produced across the resistor, so the shunt resistor is
designed based on this principle.
• The main benefits of these sensors are less cost,
response speed is fast, and accuracy is high whereas
the drawbacks are; the measurement circuit is not
isolated electrically from the flow of the current being
measured. This is appropriate in small amplitude and
low-frequency current measurements.
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Hall Effect Current Sensors
• Hall current sensor is made according to the Hall effect and Ampere’s
law principles. These sensors are used for measuring both AC & DC
currents with up to 100 KHz frequency. These sensors mainly include a
Hall effect device, core, and signal conditioning circuitry. They operate
based on the Hall Effect which states that, once current is supplied
throughout a conductor then it forms a magnetic field.
• If this conductor is arranged in another magnetic field, then the
magnetic field generated by the conductor will communicate with the
external magnetic field so that electrons move to a single side of the
conductor. So, this will create a voltage that is proportional to the flow
of current throughout it & can be measured.
• The main benefits of these sensors are good isolation & high precision
whereas their drawbacks are; the influence speed is very slow. It has
high precision and good isolation and the disadvantages are; the
influence speed is slow & small current measurement lacks accuracy.
61

Current Transformer
• A current transformer is also known as a current sensor which works
based on the electromagnetic induction principle. The main function of
this is to change the main large current value into a second smaller
current value for measurement & protection purposes.
• A current transformer mainly includes a closed iron core as well as
windings. The primary winding of this includes less number of turns &
is simply connected in series within the current line to be measured;
consequently, it frequently has the flow of current through it whereas
the secondary winding includes more turns & is simply connected in
series within the measuring instrument as well as the protection
circuit.
• Once this transformer starts working, then its secondary circuit is
closed always, thus the series coil impedance for the protection circuit
& measuring instrument is extremely small.
62

Current Sensor Circuit Diagram
The current sensor switch circuit diagram
is shown below. Generally, current
sensors are mainly used where there is a
necessity for the measurement of the
amount of current used by a particular
device or appliance. There are different
techniques are available to measure the
flow of current. So in this circuit, we are
using a Hall effect current sensor like
ACS712 IC.
ACS712 IC Pin Configuration
The ACS712 IC includes 8-pins where each
pin and its function is discussed below. 63

ACS712 IC Pin Configuration
• Pins 1 & 2 (IP+): These are positive terminals that are
used for sensing current.
• Pins 3 & 4 (IP-): These are negative terminals that are
used for sensing current.
• Pin5 (GND): This is a Ground pin.
• Pin6 (FILTER): This pin is used for the external capacitor
that sets the bandwidth.
• Pin7 (VIOUT): This is an analog output signal pin.
• Pin8 (VCC): This is a power supply pin.
The IC ACS712 is a low-cost Hall Effect current sensor used
to measure up to 20A current. This IC includes a copper
conduction lane through which the flow of current is
measured. The o/p voltage of this is proportional to the
input flow of the current. 64

Working
• The working of this current sensor circuit is quite
simple. Once current is supplied from Pins 1,2 and 3,4
throughout the conduction lane, then it produces a
magnetic field which is detected by the hall effect
sensor. After that, it is changed into proportional o/p
voltage. So, this equivalent o/p voltage will be attained
from the pin-1 of the ACS712 IC.
• The o/p from this circuit is used with Microcontroller’s
Analog pins & thus accurate current flow value can be
simply determined. So, this kind of current sensor
module is used in Microcontroller based applications.
65

HEADING SENSORS
66

HEADING SENSORS
• An earth's magnetic field sensor, a compass or its electrical
equivalent, the magnetic fluxgate, that provides the Heading
information from which the Autopilot computes steering
commands. The Heading Sensor is central to the control of
your Autopilot. Autopilot performance and, in many systems,
>Radar and Chart Plotter performance, will depend more on
Heading sensor accuracy than on any other system
component.
• The best steering algorithms cannot compensate for an
unstable and/or inaccurate Heading reference. Heading
sensors vary between manufacturers and differ depending on
the intended application and vessel. More recently for
improved accuracy, Heading sensors have incorporated solid-
state accelerometers and rate gyros for better performance in
rough and in particular following seas.
67

Compass Sensor
68

Compass Sensor
• The invention of the compass date’s back to the 2nd
century. It was used by the Chinese for divination and
alignment of building materials during construction. It was in
the 11th century that people started using Compass for
finding directions during navigation.
• Compass sensor is the device whose function is to give the
right directions with respect to the North and South magnetic
poles of the earth. The needle present on a compass always
points towards the geometric North of Earth. This device
makes use of principles of magnetism for operation.
• But this magnetic force of the earth is so weak that people
previously used to design compass by suspending a thin
magnetic strip. In the Compass present in smartphones
magnet is not used as a component because it causes
interference in communication.
69

Digital Compass Sensor
70

Digital Compass Sensor
• Digital Compass Sensor is actually a magnetometer that
can measure the Earth’s magnetic field. With the use of
‘Hall Effect’ and by calculating the ultralow frequency
signals coming from the North or South direction, this
sensor can calculate the orientation and direction.
71

Working Principle
• The first compass used in the 11th century was a simple
structure with a bowl of water containing a magnetic needle
floating on it. Later many improved and reliable versions were
developed. Digital Compass Sensor that is used in the
smartphone is based on the magnetometer sensor.
• The resistance of the magnetic sensor present in
magnetometer changes in proportional to the magnetic field
present in a particular direction. The magnetometer measures
the magnetic field strength and orientation.
• This information from magnetometer is stored by the CPU as
digital data. This Sensor always points towards the Geometric
North. The Compass found in electric devices is a solid-state
sensor. Usually, two or three magnetic sensors are present on
the device from which the microprocessor can read data and
detects the orientation of the device.
72

Magnetic Compass Sensor
• There are two configurations of Compass Sensors
available based on there working principle. They are
the Magnetic Compass and Gyro Compass. Magnetic
Compass contains a magnetic element to detect the
magnetic field. This magnetic element aligns itself with
magnetic lines of Earth’s magnetic field.
• Magnetic Compass points towards the magnetic pole
Earth. Whereas Gyro compass points towards the true
poles of the earth. Gyro compass consists of a rapidly
spinning wheel.
73

Gyroscope Sensor
74

Gyroscope Sensor
• Gyroscope sensor is a device that can measure and
maintain the orientation and angular velocity of an
object. These are more advanced than accelerometers.
These can measure the tilt and lateral orientation of
the object whereas accelerometer can only measure
the linear motion.
• Gyroscope sensors are also called as Angular Rate
Sensor or Angular Velocity Sensors. These sensors are
installed in the applications where the orientation of
the object is difficult to sense by humans.
• Measured in degrees per second, angular velocity is the
change in the rotational angle of the object per unit of
time.
75

Gyroscope Sensor
76

Gyroscope Sensor Working Principle
• Besides sensing the angular velocity, Gyroscope sensors can
also measure the motion of the object. For more robust and
accurate motion sensing, in consumer electronics Gyroscope
sensors are combined with Accelerometer sensors.
• Depending on the direction there are three types of angular
rate measurements. Yaw- the horizontal rotation on a flat
surface when seen the object from above, Pitch- Vertical
rotation as seen the object from front, Roll- the horizontal
rotation when seen the object from front.
• The concept of Coriolis force is used in Gyroscope sensors. In
this sensor to measure the angular rate, the rotation rate of
the sensor is converted into an electrical signal. Working
principle of Gyroscope sensor can be understood by observing
the working of Vibration Gyroscope sensor.
77

Gyroscope Sensor Working Principle
• This sensor consists of an internal vibrating element made up of crystal
material in the shape of a double – T- structure. This structure
comprises a stationary part in the center with ‘Sensing Arm’ attached
to it and ‘Drive Arm’ on both sides.
• This double-T-structure is symmetrical. When an alternating vibration
electrical field is applied to the drive arms, continuous lateral
vibrations are produced. As Drive arms are symmetrical, when one arm
moves to left the other moves to the right, thus canceling out the
leaking vibrations. This keeps the stationary part at the center and
sensing arm remains static.
• When the external rotational force is applied to the sensor vertical
vibrations are caused on Drive arms. This leads to the vibration of the
Drive arms in the upward and downward directions due to which a
rotational force acts on the stationary part in the center.
• Rotation of the stationary part leads to the vertical vibrations in
sensing arms. These vibrations caused in the sensing arm are measured
as a change in electrical charge. This change is used to measure the
external rotational force applied to the sensor as Angular rotation. 78

Inclinometer
79

Inclinometer
• An inclinometer is a sensor used to measure the magnitude of
the inclination angle or deformation of any structure. The bent
is either depicted in percentage or degrees concerning gravity.
• Inclinometer sensors are used to measure the slope gradient
during activities like tunnelling, excavation and de-watering.
Such activities affect the ground that supports the structure.
• The inclinometer installation procedure depends on the
application field. It can be installed vertically to monitor the
cut slope or any movement in the shoring wall and
embankment. To monitor the settlement of the soil above the
spot of tunnelling, inclinometers are installed horizontally.
• Inclinometer sensors are of different types. Each inclinometer
system requires a combination of equipment and sensors to
measure and collect data.
80

Inclinometer
81

Inclinometer
A digital inclinometer system is composed of the following
components:
• Inclinometer probe
• Inclinometer cable reel (marked at every 0.5 m / 1 m )
• Android Mobile Readout Unit
• Accessories: Cable Reel battery, Battery Charger,
Mobile battery, Mobile Charger
The digital inclinometer system is the most commonly
used one. For manual inclinometer probes, the two MEMS
sensors are mounted 90° to each other (biaxial). The
probe ranges to ±30° from vertical.
The data is retrieved using the traversing application. Let
us understand each of the components in detail:
82

Inclinometer
• The inclinometer probes are built using two types of
accelerometers:
• Servo-Accelerometer: The force-balanced sensing elements
housed in an inclinometer probe detect the change in tilt
(from reference). The probe consists of a couple of biaxial
servo-accelerometers. It is fitted with two sets of spring-
pressured wheels to guide the probe along the longitudinal
grooves of the inclinometer casing.
• MEMS Accelerometer: Such inclinometers are termed as
MEMS Inclinometers. Currently, the MEMS (Micro-Electro-
Mechanical Systems) technology is being used to build the tilt
sensor probe. The MEMS consist of mechanical elements,
sensors, actuators and electronics on a common silicon
substrate through microfabrication technology.
83

Inclinometer
• Acceleration causes deflection of the proof mass from its
centre position. There are 32 sets of radial fingers around the
four sides of the square proof mass. These fingers are placed
between plates that are fixed to the substrate.
• Each finger and pair of fixed plates makes up a differential
capacitor. The deflection of the proof mass is determined by
measuring the differential capacitance.
• By this method, both dynamic acceleration (i.e. shock or
vibration) and static acceleration (i.e. inclination or rotation)
can be sensed. Signal conditioning is carried out within
inclinometers so that a simple output signal is obtained.
• This output can be used in conjunction with a calibration sheet
to easily calculate the amount of tilt that has occurred.
84

THANK YOU
85

MR3491 SENSORS AND INSTRUMENTATION (UNIT III - FORCE, MAGNETIC AND HEADING SENSORS)

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