sensors , LE THANH PHUC

University of Technical Education
Ho Chi Minh City

SENSORS

Le Thanh Phuc
Faculty of Automotive Engineering
Email:
1


Thermistors
Thermistors are commonly used to
measure the temperature of liquids and
ambient air.
A thermistor is a solid-state variable
resistor made from a semiconductor material
that have very reproducible resistance
verses temperature properties.

2


Thermistors
There are two types of thermistors:
negative temperature coefficient (NTC)
thermistors and positive temperature
coefficient (PTC) thermistors.
NTC thermistors reduce their resistance as
the temperature increases, while PTC
thermistors increase their resistance as the

temperature increases.
The NTC is the most commonly used.

3


Thermistors

4


Thermistors: Water Temperature Sensor
The water temperature sensor is typically
located near the cylinder head water
outlet.

5


Position and Motion Detection Sensors
Many electronic systems require input data
concerning position, motion, and speed.
Most motion and speed sensors use a
magnet as the sensing element or sensed
target to detect rotational or linear speed.

6


Potentiometer

A common position sensor used to monitor
linear or rotary motion is the potentiometer.
A potentiometer is a voltage divider that
provides a variable DC voltage reading to the
computer.

7


Potentiometer: Vane type airflow meter
The vane type air flow meter is located in the
air induction system inlet pipe between the
air cleaner and the throttle body.

8


Potentiometer: Vane type airflow meter
The potentiometer converts the mechanical
movement of the measuring plate into a
variable voltage signal.

9


Potentiometer: Vane type airflow meter
Movement of the measuring plate and
the analog voltage signal produced by this
sensor are proportional to the volume of air
entering the intake manifold.

10


Potentiometer: Vane type airflow meter

11


Karman airflow meter

12


Karman airflow meter

Intake air flow reacting against the vortex
generator creates a swirling effect to the air
downstream, very similar to the wake created in
the water after a boat passes.

13


Karman airflow meter

14


Karman airflow meter

15


Mass Air Flow (MAF) Sensors
The Mass Air Flow Sensors converts the amount of
air drawn into the engine into a voltage
signal.

16


Mass Air Flow (MAF) Sensors
The air flow sensor is located directly in the
intake air stream, between the air
cleaner and throttle body where it can measure
incoming air.

17


Mass Air Flow (MAF) Sensors
Wheatstone Bridges
A Wheatstone bridge is nothing more than
two simple series circuits connected in parallel
across a power supply.
When all four resistors have the same value,
the bridge is balanced and the voltage sensor
will indicate a value of 0 volts.

18


Mass Air Flow (MAF) Sensors

19


Mass Air Flow (MAF) Sensors
The thermistor measures the temperature of
the incoming air.
The hot wire is maintained at a constant
temperature in relation to the thermistor by the
electronic control circuit.
An increase in air flow will cause the hot wire
to lose heat faster and the electronic control
circuitry will compensate by sending more
current through the wire.
The electronic control circuit simultaneously
measures the current flow and puts out a
voltage signal (VG) in proportion to current
20
flow.


Manifold Absolute Pressure (MAP) Sensor
In the Manifold Absolute Pressure (MAP)
sensor there is a silicon chip mounted inside a
reference chamber. On one side of the chip is a
reference pressure. On the other side is the

pressure to be measured.

21


Magnetic Pulse Generator
The components of the pulse generator are:
1. A timing disc that is attached to the
rotating shaft or cable. The number of teeth
on the timing disc is determined by the
manufacturer and depends on application.
2. A pickup coil consists of a permanent
magnet that is wound around by fine wire.

22


Magnetic Pulse Generator

23


Magnetic Pulse Generator

Position/speed sensors provide information to
the ECM about the position of a component, the
speed of a component, and the change in speed
of a component.

24

Magnetic Pulse Generator
This system consists of a gear (reluctor wheel),
that is mounted on the distributor shaft, has a
number of teeth equaled to number of engine
cylinders, permanent magnet and pick up coil
wrapped around the magnet.

25