Purpose of electronic signals
Electronic signals move information much like cars move passengers down the highway. It would be difficult to get to work without transportation, and there would be no transportation without signals.
Signals allow devices (e.g. sensors or switches) to communicate with control modules (either complicated processors or simple relays) which in turn perform or request (through more signaling) other functions to be carried out.
Signals inform the climate control of the outside air temperature or tell the brake lights the right time to illuminate.
The use of electronic signals goes far beyond the basic application of electron flow to control components, enabling complex information to be passed from one component to another.
The data (input or output) is conveyed through various forms of changing voltages, resistances, current or frequency modulation.
- AC Voltage Signals
a. Inductive signals
b. Phase shifted signals - DC Voltage Signals
a. Analog signals
b. Digital signals
c. Designated Value Signals
d. Coded Ground Signals
e. Transistor Signals
AC Voltage Signals
Two types of AC voltage signals are used:
- Inductive signals (Induced voltage)
- Phase Shifted Signals (Angle Pulse Generator)
Inductive sensors
Inductive sensors produce an AC sine wave signal. The AC voltage is induced by the shifting of a magnetic field. The sensor consists of an impulse wheel (the moving part) and a coil wound magnetic core (the stationary part).As each tooth of the impulse wheel approaches the sensor tip, the magnetic field of the sensor shifts toward the impulse wheel and induces a voltage pulse in the windings.As the teeth move away from the sensor, the magnetic field shifts back inducing a voltage pulse in the opposite direction.This shifting of the magnetic field produces an alternating current (positive to negative).
Control modules which receive this alternating current, count the impulses (shifts from positive to negative) and interpret the speed of rotation of the impulse wheel.
Typical application of inductive sensors- Crankshaft speed sensor
- Camshaft speed sensor
- Transmission input/output speed sensor
- Wheel speed sensor
Angle Pulse GeneratorAn Angle Pulse Generator Sensor acts on an existing AC voltage signal rather than produce a new one. The sensor consists of two windings (primary and secondary) that are connected together at one end and a magnetic iron core (stationary) along with a trigger wheel (movable).
The primary winding (coil) is supplied with a 120 kHz AC signal by the control module. The magnetic coupling (core) causes a voltage at the same frequency to be induced in the secondary winding. The induced frequency has a slight phase shift due the induction time delay.
The trigger wheel influences the magnetic field of the sensor and causes the phase shift to increase as the disc of the wheel moves closer to the sensor.
This changing of the phase shift (time delay) from a smaller time period to a larger time period and back again provides the control module with trigger wheel position.The angle pulse generator provides position information regardless of movement. Trigger wheel position is established with the application of an output frequency from the control module and the return of the phase shifted signal.
- Inductive signals (Induced voltage)
- Phase Shifted Signals (Angle Pulse Generator)
Inductive sensors
Inductive sensors produce an AC sine wave signal. The AC voltage is induced by the shifting of a magnetic field. The sensor consists of an impulse wheel (the moving part) and a coil wound magnetic core (the stationary part).
As each tooth of the impulse wheel approaches the sensor tip, the magnetic field of the sensor shifts toward the impulse wheel and induces a voltage pulse in the windings.
As the teeth move away from the sensor, the magnetic field shifts back inducing a voltage pulse in the opposite direction.
This shifting of the magnetic field produces an alternating current (positive to negative).
Control modules which receive this alternating current, count the impulses (shifts from positive to negative) and interpret the speed of rotation of the impulse wheel.
Typical application of inductive sensors
- Crankshaft speed sensor
- Camshaft speed sensor
- Transmission input/output speed sensor
- Wheel speed sensor
Angle Pulse Generator
An Angle Pulse Generator Sensor acts on an existing AC voltage signal rather than produce a new one.
The sensor consists of two windings (primary and secondary) that are connected together at one end and a magnetic iron core (stationary) along with a trigger wheel (movable).
The primary winding (coil) is supplied with a 120 kHz AC signal by the control module. The magnetic coupling (core) causes a voltage at the same frequency to be induced in the secondary winding. The induced frequency has a slight phase shift due the induction time delay.
The trigger wheel influences the magnetic field of the sensor and causes the phase shift to increase as the disc of the wheel moves closer to the sensor.
This changing of the phase shift (time delay) from a smaller time period to a larger time period and back again provides the control module with trigger wheel position.
The angle pulse generator provides position information regardless of movement. Trigger wheel position is established with the application of an output frequency from the control module and the return of the phase shifted signal.
DC Voltage Signals
Five types of DC voltage signals are used:- Analog signals
- Digital signals
- Designated value signals
- Coded ground signals
- Transistor signals
DC voltage signals are based on either 5 volts or 12 volts.
Analog signals Analog signals transmit information through an electrical circuit by regulating or changing the current or voltage.The voltage of the signal has no fixed value. The value may be anywhere in the operating range of the signal.
Three sources of analog signals are:- NTC signals
- PTC signals
- Potentiometers
NTC sensorsNTC (Negative Temperature Coefficient) sensors change resistance based on temperature. As the temperature goes up the resistance goes down. This decrease in resistance causes the voltage drop across the sensor to decrease and the input signal voltage at the control module decreases.
Examples of NTC sensorsIntake Air Temperature SensorThe intake air temperature sensor provides a 0-5 volt analog signal to the Engine Control Module indicating temperature of the incoming air.The intake air temperature sensor is located either in the intake manifold or integrated in the mass air flow meter.
Engine Coolant Temperature sensorA dual sensor is used for engine temperature. Operation is the same as other NTC sensors, 0-5 volt operating range, except that two independent sensors are housed in one assembly.One is for the engine temperature input to the Engine Control Module. The other sensor is used to input engine temperature to the instrument cluster.
PTC SensorPTC (Positive Temperature Coefficient) sensors also change resistance based on temperature. In a PTC sensor as the temperature goes up the resistance also goes up. The increase in resistance causes the voltage drop across the sensor to increase and the input voltage signal at the control module increases.
Typical application of a PTC type sensor.- Exhaust Temperature Sensor
- Transmission Temperature Sensor
PotentiometersA Potentiometer produces a gradually changing voltage signal to a control module. The signal is infinitely variable within the operating range of the sensor.This varying voltage reflects a mechanical movement of position of the potentiometer wiper arm and its related components.
Digital SignalsDigital signals transfer information through an electrical circuit by switching the current on or off. Unlike analog signals which vary voltage, a digital signal has only two possible states, control voltage or 0 voltage.
Two types of Digital Signals:- Switched (High/Low) Signals
- Modulated Square Wave Signals
Switched B+ (High/Low) SignalThis DC voltage signal produces a YES/NO type input to the control module. The voltage level will indicate a specific operating condition.
Typical application of Switched B+- Ignition switch
- Seat belt switch
- Light switch
- Hall effect switch
- Reed switch
Switched B- (High/Low) SignalThis ground signal produces a YES/NO type input to the control module. The voltage level will indicate a specific operating condition.
Typical application of Switched B-- Door position switch
- Kickdown position switch
- A/C pressure switch
Modulated Square WaveA modulated square wave is a series of high/low signals repeated rapidly.Like the switched signals (B+, B-) the square wave has only two voltage levels. A high level and low level.A modulated square wave has 3 characteristics that can be modified to vary the signal:- Frequency
- Pulse width
- Duty cycle
FrequencyThe frequency of a modulated square wave signal is the number of complete cycles or pulses that occur in one second. This number of cycles or frequency is expressed in Hertz (Hz). 1 Hz = 1 complete cycle per second.
An output function may use a fixed or varied frequency.
Pulse WidthThe Pulse Width of a square wave is the length of time one pulse is ON. Vehicle systems may use fixed or varied ON times or pulse width. Pulse width is expressed in milliseconds (ms).
Duty CycleThe duty cycle of a square wave is the ratio of ON time to OFF time for one cycle. Duty cycle is expressed in %. Vehicle systems use both fixed duty signals and variable duty cycle signals.
Hall Effect SensorsHall effect sensors produce a modulated square wave. Hall effect sensors are electronic switches that react to magnetic fields to rapidly control the flow of current or voltage ON and OFF.
The hall sensor consists of an epoxy filled non-magnetic housing containing a hall element and a magnet and a trigger wheel. The hall element is a thin non-magnetic plate which is electrically conductive (Voltage will flow through the plate). Electron flow is equal on both sides of the plate.
Since everything between the magnet and the hall element is non-magnetic the magnet (magnetic field) has no effect on the current flow.
As a metal disk or solid area of a toothed wheel, flywheel or other trigger device approaches the sensor, a magnetic field is created between the magnet and the disk.
The magnetic field cause the electron flow to stop on one side of the plate. Electrons continue to flow on the other side of the plate. The hall sensor signal is a measurement of the voltage drop between the two sides of the plate or element.
When the magnetic field increases (disc or solid toothed area in front of sensor) the volta 1ge drop across the two sides of the element increases. High voltage on one side, little on the other. The signal output from the sensor is High,As the disc moves away from the sensor the magnetic fields weakens and is lost. The loss of the magnetic field (bank toothed or open area of the wheel in front of the sensor) produces very little voltage drop across the two sides of the element. The output signal is low.This rapid switching of the voltage ON/OFF produces a HIGH/LOW signal that the control module uses to recognize speed and position.
Examples of Hall Effect Sensors
Motor Position Hall SensorsHall sensors are used on many electric motors to monitor speed and position. (i.e. electric window motors and sunroof motors.)The hall effect principal is the same except the magnet is placed on the shaft of the motor.The magnet is aligned to rotate in a precise position in front of the element. The polarization of the magnetic ring causes a polarity switch in the hall element to occur as it rotates.The square wave produced provides speed and position information to the control module.
Wheel Speed Hall Effect SensorsHall effect sensors are used to indicate wheel speed.Conventional hall effect sensors use three wires, power supply (usually 5v or 12v) a ground wire and a signal wire back to the control module.The hall effect sensors used as wheel speed sensors are unique in that they are two wire hall effect sensors.The two wire sensors eliminate the separate ground wire and the signal wire functions as the ground also.The unique two wire arrangement provides the control module with a HIGH/LOW signal having a low voltage of 7.5 volts and a high voltage of 2.5 volts.Typical application of hall effect sensors- Crankshaft sensors
- Camshaft sensors
- Wheel speed sensors
- Motor position and speed sensors (Window motor, sunroof motor)
Five types of DC voltage signals are used:
- Analog signals
- Digital signals
- Designated value signals
- Coded ground signals
- Transistor signals
DC voltage signals are based on either 5 volts or 12 volts.
Analog signals
Analog signals transmit information through an electrical circuit by regulating or changing the current or voltage.
The voltage of the signal has no fixed value. The value may be anywhere in the operating range of the signal.
Three sources of analog signals are:
- NTC signals
- PTC signals
- Potentiometers
NTC sensors
NTC (Negative Temperature Coefficient) sensors change resistance based on temperature. As the temperature goes up the resistance goes down. This decrease in resistance causes the voltage drop across the sensor to decrease and the input signal voltage at the control module decreases.
Examples of NTC sensors
Intake Air Temperature Sensor
The intake air temperature sensor provides a 0-5 volt analog signal to the Engine Control Module indicating temperature of the incoming air.
The intake air temperature sensor is located either in the intake manifold or integrated in the mass air flow meter.
Engine Coolant Temperature sensor
A dual sensor is used for engine temperature. Operation is the same as other NTC sensors, 0-5 volt operating range, except that two independent sensors are housed in one assembly.
One is for the engine temperature input to the Engine Control Module.
The other sensor is used to input engine temperature to the instrument cluster.
PTC Sensor
PTC (Positive Temperature Coefficient) sensors also change resistance based on temperature. In a PTC sensor as the temperature goes up the resistance also goes up. The increase in resistance causes the voltage drop across the sensor to increase and the input voltage signal at the control module increases.
Typical application of a PTC type sensor.
- Exhaust Temperature Sensor
- Transmission Temperature Sensor
Potentiometers
A Potentiometer produces a gradually changing voltage signal to a control module. The signal is infinitely variable within the operating range of the sensor.
This varying voltage reflects a mechanical movement of position of the potentiometer wiper arm and its related components.
Digital Signals
Digital signals transfer information through an electrical circuit by switching the current on or off. Unlike analog signals which vary voltage, a digital signal has only two possible states, control voltage or 0 voltage.
Two types of Digital Signals:
- Switched (High/Low) Signals
- Modulated Square Wave Signals
Switched B+ (High/Low) Signal
This DC voltage signal produces a YES/NO type input to the control module. The voltage level will indicate a specific operating condition.
Typical application of Switched B+
- Ignition switch
- Seat belt switch
- Light switch
- Hall effect switch
- Reed switch
Switched B- (High/Low) Signal
This ground signal produces a YES/NO type input to the control module. The voltage level will indicate a specific operating condition.
Typical application of Switched B-
- Door position switch
- Kickdown position switch
- A/C pressure switch
Modulated Square Wave
A modulated square wave is a series of high/low signals repeated rapidly.
Like the switched signals (B+, B-) the square wave has only two voltage levels. A high level and low level.
A modulated square wave has 3 characteristics that can be modified to vary the signal:
- Frequency
- Pulse width
- Duty cycle
Frequency
The frequency of a modulated square wave signal is the number of complete cycles or pulses that occur in one second. This number of cycles or frequency is expressed in Hertz (Hz). 1 Hz = 1 complete cycle per second.
An output function may use a fixed or varied frequency.
Pulse Width
The Pulse Width of a square wave is the length of time one pulse is ON. Vehicle systems may use fixed or varied ON times or pulse width. Pulse width is expressed in milliseconds (ms).
Duty Cycle
The duty cycle of a square wave is the ratio of ON time to OFF time for one cycle. Duty cycle is expressed in %. Vehicle systems use both fixed duty signals and variable duty cycle signals.
Hall Effect Sensors
Hall effect sensors produce a modulated square wave. Hall effect sensors are electronic switches that react to magnetic fields to rapidly control the flow of current or voltage ON and OFF.
The hall sensor consists of an epoxy filled non-magnetic housing containing a hall element and a magnet and a trigger wheel. The hall element is a thin non-magnetic plate which is electrically conductive (Voltage will flow through the plate). Electron flow is equal on both sides of the plate.
Since everything between the magnet and the hall element is non-magnetic the magnet (magnetic field) has no effect on the current flow.
As a metal disk or solid area of a toothed wheel, flywheel or other trigger device approaches the sensor, a magnetic field is created between the magnet and the disk.
The magnetic field cause the electron flow to stop on one side of the plate. Electrons continue to flow on the other side of the plate.
The hall sensor signal is a measurement of the voltage drop between the two sides of the plate or element.
When the magnetic field increases (disc or solid toothed area in front of sensor) the volta 1ge drop across the two sides of the element increases. High voltage on one side, little on the other. The signal output from the sensor is High,
As the disc moves away from the sensor the magnetic fields weakens and is lost. The loss of the magnetic field (bank toothed or open area of the wheel in front of the sensor) produces very little voltage drop across the two sides of the element. The output signal is low.
This rapid switching of the voltage ON/OFF produces a HIGH/LOW signal that the control module uses to recognize speed and position.
Examples of Hall Effect Sensors
Motor Position Hall Sensors
Hall sensors are used on many electric motors to monitor speed and position. (i.e. electric window motors and sunroof motors.)
The hall effect principal is the same except the magnet is placed on the shaft of the motor.
The magnet is aligned to rotate in a precise position in front of the element. The polarization of the magnetic ring causes a polarity switch in the hall element to occur as it rotates.
The square wave produced provides speed and position information to the control module.
Wheel Speed Hall Effect Sensors
Hall effect sensors are used to indicate wheel speed.
Conventional hall effect sensors use three wires, power supply (usually 5v or 12v) a ground wire and a signal wire back to the control module.
The hall effect sensors used as wheel speed sensors are unique in that they are two wire hall effect sensors.
The two wire sensors eliminate the separate ground wire and the signal wire functions as the ground also.
The unique two wire arrangement provides the control module with a HIGH/LOW signal having a low voltage of 7.5 volts and a high voltage of 2.5 volts.
Typical application of hall effect sensors
- Crankshaft sensors
- Camshaft sensors
- Wheel speed sensors
- Motor position and speed sensors (Window motor, sunroof motor)