Electrical M07 Sensors en TXT

7/22/2019 Electrical M07 Sensors en TXT

1/28Caterpillar: Confidential Yellow

GlobalManpowerDevelopMent

electronIcStroubleShootInGIltSwItcheS/SenSorS/SolenoIDSMoDule7 - textreference

Serv1877

electronics troubleshooting IltModule 7 - Switches/Sensors/Solenoids

text reference

2010 Caterpillar Inc.


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Caterpillar: Confidential Yellow

SERV1877 - 03/10 Module 7 - Switches/Sensors/Solenoids-2-

2_1

Switches

Electronic control systems use several types of switches. Switches may eithermonitor an engine or machine parameter or may be operator activated. They allhave similar functions and are typically two-state devices (ON or OFF) that providepower or grounded inputs in order to control devices.


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ParameterMonitored Switch Makeup

Temperature Variable Input with Thermistor or Thermocouple

PressureStrain Gauge with Variable Resistor and SwitchBellows w/Induction or Capacitor and Switch

Fluid Flow Paddle with Switch

OperatorActivated

- Toggle- Push / Pull- Momentary (Hold)- Push to Set / Push to Release

SWITCHES (ON / OFF INPUT DEVICES)

3_1The above chart shows switches (on/off input devices) classified by the parametemonitored and the switch makeup. Temperature, pressure, fluid flow, and coolan

level switches include a variable resistor or some other method of turning the switcon or off such as a thermocouple. When the machine conditions exceed or decreasbelow a specified limit, the switch opens (or closes) and sends a signal to the ECU.Operator activated switches send a signal to the ECU when the switch is manuallactivated by the operator.


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Rear Brake

4_1

Main Display Module

GNBK

BK 18BK 18

T

Rear Brake Oil

Temperature Switch

temperature Switch

4_2

The top photo shows a brake oil temperature switch (arrow) located on an articulatedtruck. The temperature switch contacts are normally closed. When the engineis running and brake oil temperature is within the desired range determined byengineering, the contacts stay closed and complete the ground circuit. The switchopens once the brake oil temperature exceeds an acceptable limit, alerting theoperator of the condition.

This type of temperature switch can be tested using a digital multimeter on the voltsor ohms scale. An excessive voltage drop across the terminals would indicate adefective switch.


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2Brake Oil Pressure 20

B

5_1

Main Display Module

BK 16

PK 16

RD 16

BK 16

Brake OilPressure Switch

5_2

pressure Switch

The top photo shows a brake oil pressure switch (arrow). The pressure-type switchcontacts are normally open (engine not running/low oil pressure). When the engineis running and brake oil pressure is within the desired range, the contacts close andcomplete the ground circuit.

If brake oil pressure drops to a level where the contacts open, the switch will interruptthe ground circuit signal to the ECU, causing the ECU to activate a fault condition.In the case of a broken wire, the ECU will interpret the signal in the same manner asa low pressure event.

This type of pressure switch can be tested using a digital multimeter on the voltsor ohms scale. An excessive voltage drop across the terminals when adequate

pressure is present would indicate a defective switch.


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6_1

Engine ECM

GroundBU 16

2 BK 16BK 18BK 18

Coolant Flow 18 Coolant Flow Switch

6_2

flow Switch

The top photo shows an example of a coolant flow switch. The flow switch is apaddle type and is normally open, closing once there is sufficient fluid flow. If flow isrestricted, the switch will interrupt the ground circuit signal to the ECU, causing theECU to activate a fault condition. In the case of a broken wire, the ECU will interpretthe signal in the same manner as reduced or no flow.

This type of switch can be tested using a digital multimeter on the volts or ohms scale.An excessive voltage drop across the terminals when adequate flow is present (orwhen the paddle is hand actuated) would indicate a defective switch.


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Sensor r Ret r 12 BN

Parking BrakeOp tc 44

16 1PK 16

7_1

Transmission ECM J1

Parking

Brake Switch

operator-activated Switch

7_2

Operator activated switches send a signal to the ECU when activated by the operator.The switch opens or closes and sends a signal to the ECU informing the ECU toperform an action. In this application a parking brake switch (arrow) on an articulatedtruck sends a signal to the ECU when actuated by the operator. The ECU processesthe signal and sends an output signal to engage the parking brake.

This type of switch can be tested using a digital multimeter on the volts or ohmsscale. An excessive voltage drop or excessive resistance across the terminals whilethe switch is closed would indicate a defective switch.


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ParameterMonitored SensorMakeup Active orPassive DMMMeasurements

Speed Pickup Coil Passive (2 Wire) Volts / Hz / OhmsHall Effect Active (2/3/4 Wire) Volts / Hz / Duty Cycle

TemperatureVariable Resistor Passive (2 Wire) Volts / OhmsVariable Resistor Active (3 Wire) Volts / OhmsVariable Resistor Active (3 Wire) Volts / Hz / Duty Cycle

Pressure Strain Gauge withVariable Resistor

Active (3 Wire) VoltsActive (3 Wire) Volts / Hz / Duty Cycle

PositionVariable Resistor Active (3 Wire)

Volts / Hz / Duty CycleHall Effect Active (3 Wire)Magnetostrictive Active (3 Wire)

Fuel Level Variable Resistor Passive (2 Wire) Volts / OhmsUltrasonic Active (4 Wire) Volts / Hz / Duty Cycle

SENDERS / SENSORS (VARIABLE INPUT DEVICES)

8_1Sensors

Sensors (variable input devices) can be classified in several ways as illustrated ithe chart above. This chart shows the typical sensors and senders found on Caengines and machines.

The types of senders and sensors in this chart are classified by the parametermonitored. Other sensor characteristics include:

Sensor Makeup: Internal components that determine the type of signalproduced.

Active or Passive: An active sensor receives power from the ECU orbattery and must be powered to check operation. A passive sensordoes not require power from the ECU and can be tested without powerapplied.

DMM Measurements: Type of electronic signals for a sensor that adigital multimeter can measure.

NOTE: Most variable input devices are referred to as sensors. The fuel leveinput device with a variable resistor is normally referred to as a sender. Alvariable input devices will be referred to as sensors in this presentation.


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Do not have to be powered inorder to test.

test off engine or machine(static test).

9_1 9_2

passive Sensors

Passive sensors are typically two-wire sensors, with the exception of single-wiresenders. Passive sensors do not require ECU or battery power in order to functionand test. Testing can usually be accomplished by checking the resistance of the

sensor. All passive sensors will be of the analog type.

Pin assignments for passive sensors are as follows:

Position 1: Signal

Position 2: Return/Ground


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10_1

10_2

active Sensors

Active sensors are typically three-wire sensors, but can be two- or four-wire. Activesensors require ECU or battery power in order to function and test. Active sensorsfall into one of two categories:

Analog (top photo): A signal that varies smoothly over time and inproportion to the measured parameter. These signals are typically DCvoltage.

Digital (bottom photo): Digital signals are usually associated withcomputerized electronic controls and measuring devices. The signal(s)will switch between two distinct levels, such as 0 to +10 Volts, or moresimply stated as low and high. The internal electronics of a sensordetermine the amplitude or level.

Pin assignments for active sensors are as follows:

A or 1 position: Power

B or 2 position: Return/Ground

C or 3 and 4 position: Signal


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DCV

olts

+

0Pressure (kPa)

11_1

analog Signals

As previously mentioned, an analog signal is a signal that varies smoothly over timeand in proportion to the measured parameter. Analog signals on Cat equipment aretypically AC or DC voltage.

The above illustration shows a DC analog signal trace of a pressure sensor. Thistype of electronic signal is proportional to the amount of pressure sensed in a system.

As pressure increases, the resistance of the sensing device changes. The change inresistance, and thereby voltage, would be sensed by the ECU.

NOTE: Analog sensors that have a DC output will have a typical operatingrange of 0.2 volts to 4.8 volts. Voltage ranges may be different, depending onapplication.


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One Cycle

0

Time12_1

The above illustration depicts a sine wave produced by analog speed/timing sensors.Sine waves are types of signals that change direction (alternating current). In the

above example, the voltage rises to a peak positive value, drops to zero, reversespolarity, rises to a peak negative value, and returns to zero. One positive and onenegative alternation produces one cycle. The cycle is repeated continuously.

The number of cycles that occur in one second is called frequency, expressed in Hertz(Hz). As the speed of the measured parameter increases, so will the frequency.


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hall effect: varying requency,onstant Duty ycle

pwM: onstant requency,varying Duty ycle.

High

Two Distinct

Amplitude Levels

Low

13_1

Digital Signals

As previously stated, digital signals switch between two distinct levels such as 0 to+10 Volts, or more simply stated as high and low. The internal electronics of aspecific device determine the amplitude or level. Digital signals on Cat equipment

are typically of the Hall-Effect or pulse width modulated (PWM) type.

The above illustration depicts a typical Hall-Effect signal. Hall-Effect sensorsoperate using a current field and a piece of iron (gear tooth). When the gear toothis introduced perpendicular to the current field, all of the electrons are forced toone side of the semiconductor (rememberlike forces repel and opposites attract).When current is forced to one side of a semiconductor, a difference in potential(differential voltage change) can be detected. The gear tooth moving across the Hallcell gives a highstate. The lowstate indicates the Hall cell is located in the valley

between two teeth.

Digital signals created by Hall-Effect will have a frequency that varies with the speedof the parameter being measured, and will typically have a constant duty cycle of50%.


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PULSE WIDTH MODULATION

+ OnON (80%) OFF (20%)

0

Off One Period14_1

The above illustration shows a PWM signal. A PWM signal is measured in dutcycle, which is defined as % time on (high) vs. % time off (low) for one pulse. In th

example above, the signal is on (or high) for 80% of the pulse and off (or low) for 20of the pulse. This would indicate a duty cycle of 80%.

On Cat equipment, a position sensor would be a good example of a device thaproduces a PWM signal. A PWM signal has a constant frequency output and thduty cycle (percentage of time on versus time off) of the signal varies as condition(rotary position) change. The output of the sensor is sent to an ECU where the signais processed.


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SERV1877 - 03/10 -15- Module 7 - Switches/Sensors/Solenoids

Sensor ypes

15_1

Sensors convert a physical parameter into an electronic signal. Electronic controlsuse this signal (input information) to monitor engine and machine conditions anddetermine appropriate output signals.

Several different types of sensors provide this input information to the ECU. Theseinclude:

Speed/Timing

Temperature

Pressure

Position

Fluid Level


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basically a small generator.

he Speed/ iming sensorprovides signals to the .

he signals are created as thetiming wheel rotates past thesensor pickup.

unique pattern of teeth indicatesengine position (timing) to the

each tooth is spacedapart the same number ofdegrees, with one extra tooth

in the pattern. he detectsthis extra tooth and uses it asa reference point to determinetiming.

PASSIVE SPEED SENSORS

- Two-Wire Sensor

- Magnetic Pickup Coil

16_1 16_2

DMM MEASUREMENTS

- Volts

- Hz

- Ohms

16_3 16_4

A passive (two-wire) magnetic frequency-type sensor converts mechanical motion toan AC voltage. A typical magnetic pickup consists of a coil, pole piece, magnet, and

housing. The sensor produces a magnetic field that, when altered by the passage ofa gear tooth, generates an AC voltage in the coil. The AC voltage and the frequencyof the AC signal is proportional to speed.

Magnetic pickup sensors rely on the distance between the end of the pickup andthe passing gear teeth to operate properly. Typically, when the pickup is installed, itis turned in until it makes contact with the top of a gear tooth and then turned back

out a partial turn before it is locked in place with a locking nut. A weak signal mayindicate that the sensor is too far away from the gear. It is important to check thespecifications when installing these sensors to insure the proper spacing. Variablegap speed sensors are no longer used on new production equipment as fixed gapsensors are becoming more commonplace.

Magnetic engine speed sensors may be used in pairs. One sensor is specificallydesigned for optimum performance at slower engine speeds which occur duringcranking and when the engine first starts. The other sensor is designed for optimumperformance at normal engine operating speeds. The mounting for the sensorsdiffer from each other to keep them from being interchanged.


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Although the sensors have an optimum operating range, the ECU will use the signalfrom the remaining sensor as a backup in case of a failure.

A magnetic pickup may be checked for both static and dynamic operation. With thepickup disconnected from the machine electrical harness, a resistance reading of thepickup coil (measured between pins) should indicate a coil resistance referenced in

the specifications. The resistance value differs between pickup types, but an infiniteresistance measurement would indicate an open coil, while a zero reading wouldindicate a shorted coil.


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ower speed sensitivity; muchmore accurate than mag pickup

type

all are three-wire ( ctive)

Dependent on metal passingthough a magnetic field

requency (hz) varies

Duty constant

Square wave signal

voltage may change some butis a signal carrier, not the mainsignal to be measured

ACTIVE SPEED SENSORS

- Two, Three, or Four-Wire

- Hall-Effect

18_1 18_2

Engine ECU

SPEED SENSOR CIRCUIT

J1

DMM MEASUREMENTS+V SensorSupply

Sensor Ground

Return

11 OR 18 A

BR 18 B

YL 18 C

12

OR 18

BK 18

YL 18

+V

Ground

Signal

Engine

Speed

Sensor

-Volts

- FrequencyEngine Speed 62

18_3 18_4

Some Caterpillar electronic systems use a Hall-Effect sensor for detecting magneticfields. The electronic transmission control uses this type of sensor to determine

transmission output speed, and the electronic unit injection system uses this type ofsensor to provide pulse signals for determining the speed and timing of the engine.

Both sensor types have a Hall cell (sensing element) located in the tip of the sensor.As a gear tooth passes the Hall cell, the change in the magnetic field produces a

small signal. The internal electronics of the sensor process the signal and sends adigital signal to the ECU.

The sensing element is extremely accurate because it is not speed dependent. Thesensing element operates down to 0 rpm over a wide temperature operating range.


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19_1

The timing measurement function of a speed/timing sensor uses a change in themagnetic field as a gear tooth passes to determine a tooth edge. A unique tooth

pattern on the timing wheel allows the ECU to determine crankshaft position, directionof rotation, and rpm. The ECU counts each pulse and determines speed, memorizesthe pattern (unique tooth pattern) of the pulses, and compares that pattern to adesigned standard to determine crankshaft position and direction of rotation.

This view shows a timing wheel and sensor. As each square gear tooth (arrow)passes the cell, the sensing element generates a small signal. If the signal is belowaverage (gap), the output will be low. If the signal is above average (tooth undercell), the output will be high.


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SERV1877 - 03/10 -20- Module 7 - Switches/Sensors/Solenoids

20_1

temperature Sensors

Temperature sensors measure the temperature of coolant, oil, intake air, fuel,exhaust, etc. Temperature sensors can be active (three-wire) or passive (two-wire).

This sensor includes a temperature-sensitive variable resistor (thermistor). Thevoltage drops of passive sensors and the voltage output of active analog sensorscorrelate to a specific temperature. On this type of temperature sensor, the signal(DC Volts) can be checked with power ON. The sensor resistance of passive sensorscan be checked with power OFF.

Active digital temperature sensors also use a thermistor that is sensitive to changesin temperature. The circuitry inside the sensor body converts the analog output ofthe thermistor to a PWM signal, which is sent to the ECU.


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21_1

pressure Sensors

Pressure sensors are used to measure pressures of oil, fuel, intake manifold (boost),atmosphere, crankcase, injection actuation, etc. Most pressure sensors found onCat equipment are active (three-wire) analog sensors.

Pressure sensors contain a strain gauge which changes resistance when a pressureis applied to it. The sensor circuitry detects this change in resistance and outputs avoltage in accordance with this resistance. The voltage output of a pressure sensorcorrelates to a specific pressure.


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23_1

Magnetostrictive position Sensor

A magnetostrictive position sensor is shown in the above photo. This type of positionsensor provides a PWM signal to the ECU, indicating cylinder position.

In a magnetostrictive sensor, a pulse is induced in a specially-designedmagnetostrictive wave guide by the momentary interaction of two magnetic fields.The magnetostrictive principle is defined as a change in resistance when a magneticfield is applied perpendicular to the current flow in a thin strip of ferrous material.


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24_1

In magnetostrictive sensors, a thin piece of wire (wave guide) is placed inside aprotective tube. The wave guide transmits the input and output signals. An electronic

current (input) pulse from the sensor electronic assembly creates a magnetic fieldaround the protective tube. The magnetic field interacts with the position magnetsmagnetic field and causes the wave guide to twist. This twist is the return signal thatis sent back to the sensor electronics at a sonic speed along the wave guide.

The position of the moving magnet is precisely determined by measuring the elapsedtime between the release of the electronic pulse and the arrival of the return signal(wave guide twist).


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25_1

level Sensors

A level sender assembly is located in the top or side of a tank and measures thedepth of fuel or oil in the tank.

The depth of liquid in the tank determines the position of a float. This float will beattached to a lever or a spiral rod. The float will cause the lever to move up or down,or the float will travel up or down the spiral rod, rotating the rod as it moves. Thesender is attached to the lever or rod, and changes resistances as the lever movesup and down, or as the rod rotates. This resistance is measured by the ECU or amechanical gauge.


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26_1

Some Cat machines are equipped with an ultrasonic level sensor. This type of sensoris used on fuel systems and replaces older types of sensors that used a resistive

sending unit inside the fuel tank.

The ultrasonic fuel level reacts to the level of fuel in the tank. The sensor emits anultrasonic signal that travels up a guide tube in the tank. The signal is reflected off ofa metal disk on the bottom of a float that rides on the fuel and is directed back to thesensor. The sensor measures the amount of time it takes for the signal to leave thesensor, reflect off the disk, and return to the sensor.

The sensor has four contacts. The open or grounded status of contact three on theconnector tells the ECU whether the sensor is installed in a deep tank or a shallowtank. Contact three should be open for a deep tank and grounded for a shallowtank.

Troubleshooting procedures for the ultrasonic sensor would be the same as thoseused for other PWM sensors. The ultrasonic sensor must be installed in a fuel tankto be tested.


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lthough voltage is typicallythe measured parameterfor troubleshooting, currentperforms the work.

simple compass may alsobe used to check for electricalfunctionality of a solenoid, aswell as checking the resistanceof the coil and comparing it tospecifications.

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Solenoids

Many Caterpillar electronic control systems use solenoids to perform a controlfunction. Some examples are shifting the transmission, raising an implement, fuelinjection, etc.

Solenoids are electronic devices that work on the principle of an electrical currentpassing through a conductive coil, thereby producing a magnetic field. This magnetic

field can be used to perform work, typically moving an internal spool. The type ofsolenoid that is used is determined by the task that is to be performed. Thetransmission shift solenoids in the above photo divert oil when the spools are movedby their respective magnetic field.

Solenoid valves in Cat equipment are either two-state (ON/OFF), or variable (PWM).Two-state solenoids actuate with a constant voltage, usually +12 or +24 VDC.Variable solenoids actuate using a PWM current. The less current needed, the lowerthe duty cycle of the source voltage. As more current is needed, the duty cycle isincreased.

To quickly check if a solenoid is energizing, set a screwdriver on the coil nut. If thecoil is energized, the screwdriver blade will be attracted to the nut by the coil smagnetic field.


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he red dashed line shows thebaseline current versuspressure for a solenoid valveused in the lectro- ydraulicImplement System. he areabetween the two solid lines is theacceptable tolerance bands forsolenoid valve performance.

600

500

400

300

200

100

0

0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0

Solenoid Current (Amps)

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PWM solenoids receive a varying PWM current from their respective ECU. A fault isrecorded if the ECU senses the signal to the actuator solenoid as open, shorted to

ground, or shorted to battery.

The above graph shows the relationship between the current sent by the ImplementECU to the pilot actuator solenoids and the resulting pilot pressure.

Electrical M07 Sensors en TXT

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