Experiment-6: Study of various sensors and detectors

Aim: To know the various sensors used in modern vehicle and their working
Apparatus: Vehicle fitted with sensors

Theory:
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 (today mostly electronic) instrument. For example,
a mercury-in-glass thermometer converts the measured temperature into expansion and
contraction of a liquid which can be read on a calibrated glass tube. A thermocouple converts
temperature to an output voltage which can be read by a voltmeter. For accuracy, most sensors
are calibrated against known standards.
Sensors are used in everyday objects such as touch-sensitive elevator buttons (tactile sensor)
and lamps which dim or brighten by touching the base. There are also innumerable applications
for sensors of which most people are never aware. Applications include cars, machines,
aerospace, medicine, manufacturing and robotics.

Electronic Sensor
A sensor is something that tells something about its environment. An electronic sensor is a
sensor that tells this information about its environment by creating an electrical signal. This
signal should change as the thing it is measuring changes.
In your house you have a thermostat which controls the heat. It measures the temperature of
the house, and converts this to an electrical signal. This signal is then sent down wires, back to
the heater itself. When the signal says its too cold, the heater comes on.
There are many different things to measure -- heat, light, humidity, sound level; weight etc. each
of these requires a different sensor. just how this sensor converts say weight, to electricity, is a
story of its own, and each sensor has this physics. It can be simple or complicated. But in the
end they convert their signals to something that can be sent down a wire, or sent over a radio
wave etc.
Types of Sensors
Hall Sensors
A Hall Effect sensor is a transducer that varies its output voltage in response to a magnetic
field. Hall Effect sensors are used for proximity switching, positioning, speed detection, and
current sensing applications.
In its simplest form, the sensor operates as an analog transducer, directly returning a voltage.
With a known magnetic field, its distance from the Hall plate can be determined. Using groups of
sensors, the relative position of the magnet can be deduced.
Electricity carried through a conductor will produce a magnetic field that varies with current, and
a Hall sensor can be used to measure the current without interrupting the circuit. Typically, the
sensor is integrated with a wound core or permanent magnet that surrounds the conductor to be
measured.
Frequently, a Hall sensor is combined with circuitry that allows the device to act in a digital
(on/off) mode, and may be called a switch in this configuration. Commonly seen in industrial
applications such as the pictured pneumatic cylinder, they are also used in consumer
equipment; for example some computer printers use them to detect missing paper and open
covers. When high reliability is required, they are used in keyboards.
Hall sensors are commonly used to time the speed of wheels and shafts, such as for internal
combustion engine ignition timing, tachometers and anti-lock braking systems. They are used
in brushless DC electric motors to detect the position of the permanent magnet. In the pictured
wheel with two equally spaced magnets, the voltage from the sensor will peak twice for each
revolution. This arrangement is commonly used to regulate the speed of disk drives.
Inductive Sensor
An inductive sensor is an electronic proximity sensor, which detects metallic objects without
touching them. The sensor consists of an induction loop. Electric current generates a magnetic
field, which collapses generating a current that falls asymptotically toward zero from its initial
level when the input electricity ceases. The inductance of the loop changes according to the
material inside it and since metals are much more effective inductors than other materials the
presence of metal increases the current flowing through the loop. This change can be detected
by sensing circuitry, which can signal to some other device whenever metal is detected. .
Common applications of inductive sensors include metal detectors, traffic lights, car washes,
and a host of automated industrial processes. Because the sensor does not require physical
contact it is particularly useful for applications where access presents challenges or where dirt is
prevalent.
The crankshaft sensor measures the engine speed. It consists of a permanent magnet and an
induction coil with a soft iron core. A ring gear is mounted on the flywheel to serve as the pulse
generator (movement). There is only a small air gap between the inductive sensor and ring
gear. The magnetic flux through the coil depends on whether there is a gap or a gear tooth
opposite the sensor. A tooth bundles the stray flux of the magnet while a gap weakens the
magnetic flux.
Ultra sonic sensor/Transducer
Ultrasonic sensors (also known as transceivers when they both send and receive, but more
generally called transducers) work on a principle similar to radar or sonar which evaluate
attributes of a target by interpreting the echoes from radio or sound waves respectively.
Ultrasonic sensors generate high frequency sound waves and evaluate the echo which is
received back by the sensor. Sensors calculate the time interval between sending the signal
and receiving the echo to determine the distance to an object.
This technology can be used for measuring wind speed and direction (anemometer), tank or
channel level, and speed through air or water. For measuring speed or direction a device uses
multiple detectors and calculates the speed from the relative distances to particulates in the air
or water. To measure tank or channel level, the sensor measures the distance to the surface of
the fluid. Further applications include: humidifiers, sonar, medical ultrasonography, burglar
alarms and non-destructive testing.
Systems typically use a transducer which generates sound waves in the ultrasonic range, above
18,000 hertz, by turning electrical energy into sound, then upon receiving the echo turn the
sound waves into electrical energy which can be measured and displayed.
Operation of the ultrasonic transducers is based on the echo-sounding principle. Short
ultrasonic pulses are sent out by the ultrasonic transducer, reflected from objects in the vicinity
and received again by the ultrasonic transducer.
The ultrasonic transducer sends the period of time required between sending the ultrasonic
pulse and receiving the first echo to the Park Distance Control (PDC) unit which, in turn,
calculates the distance to the nearest object from this period of time.
Infrared Radiation Sensor
All objects have a certain temperature and emit waves of thermal energy called infrared
radiation. The hotter an object, the more energy waves are emitted. A thermal imaging system
converts these energy waves into an image that will normally display a black and white picture.
This display works by showing the hottest objects as white, the coolest objects as black, and
features of other objects show as varying shades of grey. In this image you can see three cups
– two filled with hot coffee and one with cold water. Heat radiation is absorbed and dissipated by
virtually every solid or liquid body. Heat radiation, however, is not visible to the human eye
because it belongs in the long-wave infrared range. From a physical standpoint, this represents
electromagnetic waves with a wavelength of 8μm to 15 μm. This long-wave infrared radiation is
known as Far Infrared (FIR).
An infrared sensor is an electronic instrument that is used to sense certain characteristics of its
surroundings by either emitting and/or detecting infrared radiation. It is also capable of
measuring heat of an object and detecting motion. Infrared waves are not visible to the human
eye.
In the electromagnetic spectrum, infrared radiation is the region having wavelengths longer than
visible light wavelengths, but shorter than microwaves. The infrared region is approximately
demarcated from 0.75 to 1000µm. The wavelength region from 0.75 to 3µm is termed as near
infrared, the region from 3 to 6µm is termed mid-infrared, and the region higher than 6µm is
termed as far infrared.
Infrared technology is found in many of our everyday products. For example, TV has an IR
detector for interpreting the signal from the remote control. Key benefits of infrared sensors
include low power requirements, simple circuitry, and their portable feature.
Types of Infra-Red Sensors
Infra-red sensors are broadly classified into two types:
 Thermal infrared sensors – These use infrared energy as heat. Their photo sensitivity is
independent of wavelength. Thermal detectors do not require cooling; however, they have
slow response times and low detection capability.
 Quantum infrared sensors – These provide higher detection performance and faster
response speed. Their photo sensitivity is dependent on wavelength. Quantum detectors
have to be cooled so as to obtain accurate measurements. The only exception is for
detectors that are used in the near infrared region.
Working Principle
A typical system for detecting infrared radiation using infrared sensors includes the infrared
source such as blackbody radiators, tungsten lamps, and silicon carbide. In case of active IR
sensors, the sources are infrared lasers and LEDs of specific IR wavelengths. Next is the
transmission medium used for infrared transmission, which includes vacuum, the atmosphere,
and optical fibers.
Thirdly, optical components such as optical lenses made from quartz, CaF 2, Ge and Si,
polyethylene Fresnel lenses, and Al or Au mirrors, are used to converge or focus infrared
radiation. Likewise, to limit spectral response, band-pass filters are ideal.
Finally, the infrared detector completes the system for detecting infrared radiation. The output
from the detector is usually very small, and hence pre-amplifiers coupled with circuitry are
added to further process the received signals.
Applications
The following are the key application areas of infrared sensors:
 Tracking and art history
 Climatology, meteorology, and astronomy
 Thermography, communications, and alcohol testing
 Heating, hyperspectral imaging, and night vision
 Biological systems, photobiomodulation, and plant health
 Gas detectors/gas leak detection
 Water and steel analysis, flame detection
 Anesthesiology testing and spectroscopy
 Petroleum exploration and underground solution
 Rail safety.

Example: If your vehicle has had a diagnostic test you may for example have a code displayed
“sensor B1 S1faulty”. So what does this mean, what is B1 or S1? Well what this is suggesting is
that Bank 1 Sensor 1 is faulty. So what is Bank 1?
Bank 1 is where the Number 1 cylinder is located. This is always the forward most cylinder.
Sensor controlled systems have become an integral part of today’s automobile. A multitude of
electro-mechanical devices have become better refined and more efficient with their
application.
Automobile sensors can be classified into three basic areas: drive-train and vehicle control,
driver safety/comfort/information and emissions. They are used to monitor temperature, gases,
voltages/currents, vacuum and torque to name a few. Twenty years ago, the typical automobile
had approximately five sensors. Today, over fifty sensors are used to control everything from
braking to the fuel delivery system. Increasing awareness concerning emissions, safety and the
technology age have all played a role in the advancement of sensing systems. However, some
of the most advanced sensors have been developed to control the harmful emissions, such as
carbon monoxide (CO) and nitrogen oxide (NOx), which are byproducts of the combustion
engine.
Different types of sensors used in today’s automobile are shown as below:
The important sensors used in the vehicle are as below:-
Mass Airflow Sensors

A growing focus on reducing CO2 emissions means that mass airflow sensors are becoming
increasingly important in ensuring the optimum air fuel ratio. Mass airflow sensors are
positioned directly after the air filter in the intake manifold and supply information on
temperature, humidity and intake air volume. Despite their highly compact construction they
feature precision technology to capture information, which – together with other engine data –
enables optimum engine management.
This data includes:
- Intake air temperature
- Intake air humidity
- Intake air volume
In gasoline engines, mass airflow measurement is used in
conjunction with other sensor readings to regulate the supply of
fuel to the engine.
In diesel engines, mass airflow sensors are used to regulate
the exhaust gas recirculation rate and calculate the maximum
injection quantity.
The mass airflow sensors are exceptionally reliable and
highly capable of withstanding environmental factors. Their
dynamic measurement ability makes an important
contribution to reducing vehicle emissions.

Wheel speed sensor

The wheel speed signal is crucial for electronic systems like

ABS or ASC
Camshaft Sensor

The camshaft sensor is located in the cylinder head and reads the
camshaft sprocket to determine the position of the camshaft. This
information is required for functions such as initiating injection on
sequential injection engines, the trigger signal for the magnet valve on
pump valve injection systems and for cylinder-specific knock control.

Crankshaft Sensor
The crankshaft sensor supplies information on the crankshaft’s current
position, which the engine management system can then use to calculate
rpm. These values make it possible to determine the most economical fuel
injection and ignition timing for a vehicle.

Knock Sensor

Modern engines which allow high compression ratios have a distinct

disadvantage: their design leads to increased knocking, which can
damage the engine.
Knock sensors reliably measure the vibration of the engine block that is
characteristic of engine knocking. This allows the firing angle and other
parameters to be set such that the engine continues to function correctly
close to the knock threshold. This not only protects the engine but also
reduces fuel consumption.
To ensure maximum precision, our knock sensors deploy groundbreaking bandwidth
technology.
Pressure Sensors

MAP and T-MAP sensors measure the air pressure in the

intake manifold behind the throttle valve to determine air intake.
This information is extremely important for calculating the
amount of fuel to be injected to ensure the correct air fuel mix.
For this reason, the dynamic measurement capability of these
engine management components is crucial in reducing vehicle
emissions.
- MAP pressure sensor for turbocharged engines for measuring
air pressure behind the turbocharger (measurement range
500–3000 hPa)
- T-MAP pressure sensor with integrated temperature sensor

Oxygen Sensor

The sensor is part of the emissions control system and feeds data to
the engine management computer. The goal of the sensor is to help
the engine run as efficiently as possible and also to produce as few
emissions as possible.
A gasoline engine burns gasoline in the presence of oxygen. It turns
out that there is a particular ratio of air and gasoline that is "perfect,"
and that ratio is 14.7:1 (different fuels have different perfect ratios --
the ratio depends on the amount of hydrogen and carbon found in a given amount of fuel). If
there is less air than this perfect ratio, then there will be fuel left over after combustion. This is
called a rich mixture. Rich mixtures are bad because the unburned fuel creates pollution. If
there is more air than this perfect ratio, then there is excess oxygen. This is called
a lean mixture. A lean mixture tends to produce more nitrogen-oxide pollutants, and, in some
cases, it can cause poor performance and even engine damage.
The oxygen sensor is positioned in the exhaust pipe and can detect rich and lean mixtures. The
mechanism in most sensors involves a chemical reaction that generates a voltage (see the
patents below for details). The engine's computer looks at the voltage to determine if the
mixture is rich or lean, and adjusts the amount of fuel entering the engine accordingly.
The reason why the engine needs the oxygen sensor is because the amount of oxygen that the
engine can pull in depends on all sorts of things, such as the altitude, the temperature of the air,
the temperature of the engine, the barometric pressure, the load on the engine, etc.
When the oxygen sensor fails, the computer can no longer sense the air/fuel ratio, so it ends up
guessing. Your car performs poorly and uses more fuel than it needs to.
ECT (Engine Coolant Temperature) Sensor
An ECT sensor, or Engine Coolant Temperature Sensor is a sensor that is screwed into the
engine's block or cylinder head and is used to determine the temperature of the engine coolant.
The ECT sensor is basically a thermistor that changes resistance with temperature. When the
ECT (engine coolant temperature) is high (hotter), the
resistence is low, and when the ECT is low (cooler) the
resistence is high. This resistance reading is sent to the
vehicle's PCM/ECM (car's onboard computer) and is or can be
used to activate emission controls or turn the engine's cooling
fan on. The ECT sensor is usually a two wire sensor that uses
a 5 volt reference from the PCM with a ground signal back to the PCM. In general terms if the
ECT reading is cold the reading could be less than 0.5 volts (on the ground signal) and when
the engine is hot the reading could be around 4 volts. For specific readings for your application,
see a vehicle-specific repair manual. Note that the ECT sensor is not the same thing as a
coolant temperature SENDER. The temperature sender is typically used as the reading for the
temperature gauge on the instrument cluster.
Fuel temperature sensor:
The engine controller operates in a system called "closed loop" where it makes decisions to
control engine (emissions) operation based on many
specific factors. The Fuel temp sensor helps the engine to
know how much fuel to inject as hotter fuel is less dense
than cooler fuel, therefore it can change the emissions
level and economy if hot fuel were injected at cool fuel
rates, or vice-versa.
Seat track position sensor:
The Control Device Seat Track Position Sensor (STPS) is
contactless, self-contained and completely sealed against
the environment. It employs an advanced magnetic
circuit and retained magnet which operates with a large
sensing air gap. The compact 2-wire Hall effect-based sensor is easily packaged on the seat
and is used in vehicles with advanced air bag systems. Excellent field performance on several
OEM platforms has demonstrated that this device has proven real-world functionality and overall
value.
Window position sensor:
Power windows have been improving their performance over the years and they now use reed
sensors to control the motors as they reach their end limits. Also, if an object impedes the
window's progress, slowing the windows progress, this slowdown must be detected, particularly
when going in the closing position. This is particularly important if one's arm or hand is between
the top of the window and door. Reed Sensors have been an excellent choice capable of
accomplishing all three requirements in a reliable manner.
Humidity sensor:
A special sensor system in conjunction with the control algorithms in the Climatronic reduces
misting-up of the windows and enhances climatic comfort by
managing the humidity levels inside the car. From the data
delivered by the humidity and temperature sensor in the
base of the interior mirror, the Climatronic control unit
calculates the dew point temperature of the air – that is, the
temperature at which the air humidity would condense. An
infrared sensor remotely measures the radiated heat on the
windscreen, and calculates the window temperature. To prevent the windows from misting up,
Climatronic regulates the volume of air projected on to the windscreen and, with the compressor
switched on, also the air humidity inside the car.
Relative humidity based on interior temperature can also be kept at a pleasant level.
HVAC sensor:
Traditional vehicle cabin climate control systems attempt to regulate the temperature and
humidity for the cabin environment as a whole to a set point. Cabin Comfort Control focuses on
first identifying the comfort or thermal sensation experienced by the driver and passengers and
controlling the heating, ventilation and air-conditioning (HVAC) to ensure that this is neutral.
"Neutral" thermal sensation occurs when the occupant is neither too hot nor too cold. This
revised aim might be achieved using less energy than traditional climate control systems since:
 comfort may be achieved over a range of temperatures and thus it is not always necessary
to tightly regulate the cabin environment to a particular set point
 temperature and humidity control can be focused on the driver and passenger
 comfort tends to be context dependent (e.g. lower temperatures might be acceptable in
winter when passengers are already dressed for a cold environment; conversely higher
than usual temperatures might be acceptable (and even preferred) in a hot climate)
 natural ventilation can be preferred where the external environment allows.
Virtual sensors measure the occupant's skin temperature / humidity at several locations. The
sensors are virtual in the sense that estimates are made based on real sensors placed around
the car cabin. A key goal for this work is to identify the optimum set of real sensor positions to
maximise the quality of the estimate for all virtual sensors. The estimators are derived using
machine learning based on empirical trials with real sensors used in the virtual sensor
locations.
Park distance control sensor
The distance between the vehicle and an obstacle is measured by way of ultrasonic signals and
audibly signalled by a warning tone. This tone sequence changes
continuously corresponding to the distance between vehicle and obstacle,
indicating to the driver the distance to the obstacle. The shorter the distance
of the vehicle from the obstacle the faster the tone sequence. A continuous
tone sounds at a distance of less than 25 cm. To distinguish the sounds, the
pitch is different at the front and rear. In addition to the audible signal,
depending on the vehicle and vehicle equipment, the distance from the
obstacle is also shown visually on the display in the vehicle, in the form of a
schematic representation of the vehicle and the distance to the obstacles.
Night vision sensor
The Night Vision system provides the driver with a black-and-white image of the driving
environment ahead of the vehicle in the control display. Night Vision is a 100% passive system
without active infrared illumination. Objects situated ahead of the vehicle are shown in varying
degrees of brightness depending on the temperature of these objects. This enables the driver to
detect in good time heat-emitting objects such as, for example, persons, animals and other
vehicles.

Conclusions:

1. The students will able to define sensors and know their applications.
2. The students will be able to classify the type of sensors and their working principles.
3. The students will be able to know various types of sensors used in automobile.