05 computer input (sensor and actuator)

8/12/2019 05 Computer Input (Sensor and Actuator)

1/25

Computer Input

(Sensor and Actuator)


2/25


3/25

Sensor


4/25

Thermistor


5/25

A thermistoris made of semiconductor material whose resistance varies inversely

with temperature. For example, at -40C a typical coolant sensor has a resistance of

100,000 ohms. The resistance decreases to about 70,000 ohms at 130C.


6/25

Using the circuit shown in Figure above, if the

value of the fixed resistor is 10K ohms and the

value of the thermistor is also 10K ohms, the

voltage sensing circuit will read a voltage value of

2.5 volts. If the thermistor is a NTC, as the

ambient temperature increases its resistance

decreases. If the resistance of the NTC is now 8K

ohms, the voltage reading by the voltage sensing

circuit will now be 2.22 volts. As ambienttemperature increases and the NTC value

continues to decrease, the voltage sensing circuit

will measure a voltage decrease (Figure 10-3). If

the thermistor was a PTC, the opposite would be

true and the voltage sensing circuit would

measure an increase in voltage as the ambient

temperature increases.


7/25


8/25

Temperature Sensor TestingThe temperature sensor can be tested while they are installed in the system by backprobing

the terminals to connect a digital voltmeter or lab scope to the sensor terminals. The sensor

should provide the specified voltage drop at any temperature. The scope trace of an NTCthermistor should indicate a smooth transition from a high voltage (about 4.0 volts) to a low

voltage as the sensor warms.

Consider Figure above as an example for circuit diagnosis. Simply disconnect the

sensor and observe the voltage on the scan tool. The displayed voltage should

equal that used by the control module circuit. If the voltage displayed by the

scan tool is 0, the problem is either the signal circuit is shorted to chassis ground

or to the sensor ground circuit, or a faulty control module.

If the specified voltage is present with the sensor unplugged, use a jumper wire

to connect the two terminals at the sensor harness connector. The scan tool

should display 0 volts.

If the voltage is still 5 volts, connect the signal circuit wire to chassis ground. If

the reading is now 0 volt, the sensor ground circuit is open. While doing these

steps if the voltage is above 0 volts (but less than 5 volts), this indicatesresistance in the circuit.

0 V


9/25

Intermittent faults may be located by

using a lab scope or the data-recording

function of the scan tool. Since these

instruments indicate a change in

voltage over time, any change that

occurs on the trace that cannot

actually happen in the time frameindicates a problem with the circuit.

For example, engine temperature

cannot increase 80 degrees in 2

seconds. Since the ECT sensor is used

by some body systems (such as air

conditioning), a fault with this sensor

may result in many different customer

concerns being expressed. Figure 10-7

is a data recording of a normally

operating ECT and Figure 10-8 is a data

recording of an intermittent fault.


10/25

Diagnosting PTC Circuit Protection

Device


11/25


12/25

Pressure Sensor


13/25

Pressure SwitchPressure switches will usually use a diaphragm that works against a calibrated spring or other form of

tension (Figure 10-6). When pressure is applied to the diaphragm that is of a sufficient value to

overcome the spring tension a switch is closed. Current that is supplied to the switch now has a

completed path to ground. In a very simple warning light circuit, the closed pressure switch completed

the circuit for the bulb and alerts the driver to an unacceptable condition. For example a simple oil

pressure warning lamp circuit will use a pressure switch.

Computer monitored pressure switch circuits use the change in voltage as an indication of pressure.

When the pressure change (either from low to high or high to low) changes the state of the switch, the

voltage change is interpreted by the computer (Figure 10-7). Pressure switches are used to monitor the

presence of pressure that is above or below a setpoint; they do not indicate the exact amount of

pressure being applied.


14/25


15/25

Piezoresistive Device


16/25

Wheatstone Bridge


17/25


18/25

Position and Motion Detection Sensor


19/25

PotentiometerA 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. These sensors are typically used to determine the

position of a valve, air conditioning unit door, seat track, and so on.


20/25

Magnetic Pulse Generator


21/25

Hall-Effect Sensors

ll ff


22/25

Hall-Effect Sensors

ll ff


23/25

Hall-Effect Sensors

ll ff


24/25

Hall-Effect Sensors

H ll ff S


25/25

Hall-Effect Sensors

05 computer input (sensor and actuator)

Documents