KATHMANDU UNIVERSITY
SCHOOL OF ENGINEERING
DEPARTMENT OF ELECTRICAL AND ELECTRONICS ENGINEERING
INSTRUMENTATION LABORARTORY WORK
EEEG 306
LAB REPORT: 3
Observation of Working Principle of Different Sensors Used in
Automobile
Submitted By: Submitted To:
Prem Kr Yadav Aayush Bista
EE-Power & Control DoEEE, KU
III/I
Roll no: - 31246
Date: 2025/06/19
Experiment-III
Title: Observation of Working Principle of Different Sensors Used in Automobile
Apparatus:
Model of Sensors in Automobiles Kit
Types of Sensors:
Observe the following types of sensors in the laboratory shown by a technician.
Air-mass meter
An air-mass meter or mass air-flow sensor (MAF) measures the amount of air flowing past per unit
of time. Because the quantity of oxygen in the air stream is proportional to the measured mass
flow, this variable can be used to control combustion processes, especially in internal combustion
engines. The air-mass meter is installed between the air filter and the engine's intake pipe.
Motor vehicles are usually furnished with a hot-film air-mass meter. In this case, a measuring
surface (the hot film) is heated to a setpoint temperature by an internal circuit of the air-mass meter
(PTC). When air flows past this surface, it is cooled. The film is then re-heated by the internal
electronics to the setpoint temperature with the help of a Wheatstone bridge. The value of the
current needed to re-heat the film indicates the mass of air drawn in. This current value is converted
by the air-mass meter's internal electronics into an output voltage signal.
Advantages:
• Very fast reaction
• Very precise measurements of flow rates, especially low ones (0 to 1 m/s) • Cost-
effective
Disadvantages:
• Susceptible to soiling
• Very susceptible to mechanical damage
An air-mass meter accordingly has the following connections:
• Ground +12 V (for the heating element)
• +5 V (supply voltage for the evaluation electronics)
• Air-mass signal line
• Air-temperature signal line
Hall sensor
Discovered by Edwin Hall in 1879, the Hall effect refers to the occurrence of an electric field when
a conductor carrying an electric current is positioned in a stationary magnetic field. Perpendicular
with respect to the current flow as well as the magnetic field's alignment, the voltage vector across
the conductor is termed Hall voltage (UH) after its discoverer.
Each time a tooth space or a sector turns past the Hall sensor, it generates a Hall voltage which is
relayed to the motor control unit. Together with the signal from the crankshaft sensor, the Hall
sensor signal allows the motor control unit to determine which cylinder is currently performing the
power stroke.
Inductive sensor
As the name suggests, an inductive sensor operates on the principle of induction, according to
which a voltage is produced in a coil when it moves relative to a surrounding magnetic field. The
inductive sensor makes use of this phenomenon, permitting contactless and consequently wearfree
measurement of angles, distances and speeds.
Scope of application
• Speed measurement - e.g. on a crankshaft, gearbox or ABS
• Determination of crankshaft position
• Pulse generation for ignition
The magnetic flux through the coil depends on whether a space or mark is in front of the sensor. A
mark (i.e. cog) concentrates the magnetic field, while a space weakens the field. When the
crankshaft and gear rim rotate, each passing cog changes the magnetic field. This change induces
a voltage in the coil. The number of pulses per unit of time are a measure of the engine speed.
Dedicated spaces on the gear rim also permit the control unit to identify the engine's instantaneous
position.
NTC sensor
An NTC resistor is one whose resistance depends on temperature, i.e. its resistance drops as the
temperature rises. Consequently, an NTC resistor, or thermistor, is more conductive in the hot state
than in the cold state. NTC stands for negative temperature coefficient, indicating that the
resistance is inversely proportional to the temperature.
An NTC's reference value is its resistance at 20°C (R20) which is defined as the cold state. Because
it depends on temperature, the resistance need not be calculated, rather simply read off from
characteristics on data sheets. The circuit symbol's two opposing arrows indicate that the resistance
drops as the sensor temperature rises. NTC resistors are more conductive at higher temperatures,
their resistance being lower then. This is because a rise in temperature detaches more electrons
from their crystal bonds, making them available for conducting electricity.
NTC sensors on automobiles are frequently used for measuring:
• Coolant temperature
• Oil temperature
• External temperature
• Air-conditioning outlet temperature
• Fuel temperature (in the case of common-rail diesel engines).
Pressure sensor
A Manifold Absolute Pressure (MAP) sensor measures the absolute pressure in a suction pipe with
respect to the ambient pressure. This sensor is located between the throttle valve and the inlet
valves. When the throttle valve is closed, the piston's downward motion creates a strong negative
pressure (low absolute pressure) in the suction pipe. When the throttle valve is opened, more air
flows into the suction pipe so that the negative pressure decreases (absolute pressure rises). The
suction pipe's absolute pressure is hence a measure of the engine load.
The MAP sensor contains a piezo-membrane made of silicon crystal. Attached to the surface of
this membrane are strain-gauges, two in the middle and two more near the edges.
As the pressure exerted on it rises, the membrane bends, hence increasing the resistance of the
inner strain gauges and decreasing the resistance of the outer ones. 1 An internal evaluation
(bridge) circuit built into the sensor supplies a voltage signal ranging between about 0.2 and 4.3 V.
In the case of non-supercharged engines, the pressure ranges from well below 1 bar to about 1 bar;
in the case of turbo engines, the boost pressure can result in values of up to 2 bar. A temperature
sensor can also be built into the same housing.
Pressure sensors are being employed increasingly on motor vehicles. A distinction is generally
made between overpressure and under pressure sensors. Overpressure sensors are used, for
instance, to measure boost pressure on turbo engines, atmospheric pressure, tyre pressure and fuel
pressure in the case of diesel and petrol engines with direct fuel injection. Though these sensors
measure a wide variety of pressure ranges, they are all based on the same operating principle. The
MAP sensor can be used as a substitute for the air-mass meter.
PTC sensor
The exhaust gas temperature sensor makes use of a PTC resistor, whose value changes as a function
of the temperature. By measuring this resistance, the motor control unit can obtain information on
the exhaust gas temperature.
A PTC is more conductive at low temperatures than at high ones.
PTC resistors (positive temperature coefficient) are materials which conduct electric current more
efficiently at low temperatures than at high ones. A PTC resistor's value rises with temperature,
hence the term "positive temperature coefficient". Metals generally have a positive temperature
coefficient which, however, is much lower and essentially linear compared with the coefficients of
the components considered further below. Because PTCs heat up automatically when conducting
high currents, the motor control unit allows only low measurement currents to flow. As the PTC
heats up in the flow of exhaust gas, its resistance rises as a result. The two co-aligned arrows
indicate that the sensor's resistance is directly proportional to its temperature.
Throttle valve potentiometer
A throttle valve potentiometer serves the same purpose as a throttle valve switch, i.e. it indicates
the throttle valve's current setting to the motor control unit. Being able to precisely determine
valve's setting, the potentiometer is an advancement of the throttle valve switch. Furthermore, the
potentiometer notifies the motor control unit of the rate at which the throttle valve is being
opened / closed by the driver's actuation of the accelerator pedal. This information allows the
motor control unit to adjust the fuel mixture's rich / lean level more accurately than using signals
from a throttle valve switch.
According to Ohm's law, the applied voltage of 5 V drops fully over the length of the resistor's
path (i.e. the conductive track in this case). In other words: 5 V are present on the signal line if
the sliding contact is at its left limit, 0 V if the contact is at its right limit, and 2.5 V if the contact
is in the middle.
Assignment Questions:
1. What are the types of thermistors and show their working principle.
Ans: Thermistors are temperature sensors that change their resistance with changes in
temperature. The word "thermistor" comes from "thermal" and "resistor". There are mainly
two types of thermistors based on how their resistance behaves with temperature:
a. NTC Thermistor (Negative Temperature Coefficient)
• Working Principle: The resistance decreases when the temperature increases.
• This happens because as the temperature rises, more free electrons are available to carry
current, which makes the material more conductive.
• These thermistors are commonly used in cars to measure things like coolant temperature,
oil temperature, air temperature, or fuel temperature.
b. PTC Thermistor (Positive Temperature Coefficient)
• Working Principle: The resistance increases when the temperature increases.
• This is due to more collisions and less movement of electrons at higher temperatures in the
material.
• PTC thermistors are often used in vehicles to measure exhaust gas temperature or in circuits
for overcurrent protection.
In summary:
• NTC = resistance goes down when temperature goes up.
• PTC = resistance goes up when temperature goes up.
2. How would you determine if a sensor is failing, you can take a case of any sensors
you have observed above.
Ans: For this condition, let’s take the Air-Mass Meter (MAF Sensor) as an example. This
sensor measures the amount of air entering the engine and helps the control unit manage
fuel injection properly.
To know if the MAF sensor is failing, we must follow the given steps:
1. Check the Voltage Output:
• The sensor gives out a voltage signal that depends on how much air is flowing in.
• If the voltage doesn't change with engine speed (e.g., stuck at 0V or always showing
5V), it could be faulty.
2. Use a Scanner Tool:
• A mechanic can use an OBD-II scanner to check for error codes.
• Fault codes like P0100 – P0104 usually point to MAF sensor problems.
3. Look for Performance Issues:
• When the sensor fails, the car may show symptoms like:
▪ Poor acceleration
▪ Rough idling
▪ Engine stalling
▪ Excessive smoke or poor fuel economy
4. Do a Visual Check:
• The MAF sensor can get dirty or damaged.
• If there is dirt or oil on the sensing element, it won’t measure properly.
• Also check for loose or broken wires.
Hence, by combining all these electrical checks, performance symptoms, and diagnostic
tools, we can easily tell if a sensor like the MAF is failing or not and can be helpful in its
monitoring.
3. What are the errors from a sensor and how do you mitigate the errors.
Ans: Sensors are just like any other electronic device that can make mistakes sometimes.
These mistakes are called errors in the sensor readings.
Some of the most common types of errors in the sensors are:
a) Systematic error:
• This is when the sensor is not set properly or is poorly made.
• Example: It always shows a little too high or too low, no matter what.
b) Environmental error:
• Things like heat, dust, water, or even other electronics can cause error with the
sensor’s readings.
• Example: A temperature sensor near a hot engine might give wrong values. c)
Aging or drift:
• Over time, sensors can slowly become less accurate.
• Like people getting slower with age, sensors can too.
d) Physical damage or dirt:
• Sensors can break, get dirty, or have loose wires.
• A dirty or broken sensor just can’t do its work well and operate properly.
These errors can be minimized and solved by following these steps:
• Check and adjust (i.e. calibrate) the sensor from time to time so it gives the right
values.
• Clean the sensor if it’s dusty or oily.
• Protect it from water, heat, or damage with proper covers or housing.
• Use filters or shielding to protect from electric or magnetic noise.
• Replace old sensors before they go completely bad
