Electrical M07 Sensors en TXT

Global Manpower DevelopMent

electronIcS troubleShootInG Ilt SwItcheS/SenSorS/SolenoIDS MoDule 7 - text reference

Serv1877

electronics troubleshooting Ilt Module 7 - Switches/Sensors/Solenoids text reference

© 2010 Caterpillar Inc. Caterpillar: Confidential Yellow

SERV1877 - 03/10

-2-

Module 7 - Switches/Sensors/Solenoids

2_1 Switches Electronic control systems use several types of switches. Switches may either monitor an engine or machine parameter or may be operator activated. They all have similar functions and are typically two-state devices (ON or OFF) that provide power or grounded inputs in order to control devices.

Caterpillar: Confidential Yellow

SERV1877 - 03/10

-3-

Module 7 - Switches/Sensors/Solenoids

SWITCHES (ON / OFF INPUT DEVICES) Parameter Monitored Temperature

Switch Makeup Variable Input with Thermistor or Thermocouple Strain Gauge with Variable Resistor and Switch

Pressure Bellows w/Induction or Capacitor and Switch Fluid Flow

Paddle with Switch

Operator Activated

- Toggle - Push / Pull - Momentary (Hold) - Push to Set / Push to Release 3_1 The above chart shows switches (on/off input devices) classified by the parameter monitored and the switch makeup. Temperature, pressure, fluid flow, and coolant level switches include a variable resistor or some other method of turning the switch on or off such as a thermocouple. When the machine conditions exceed or decrease below 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 manually activated by the operator.

Caterpillar: Confidential Yellow

SERV1877 - 03/10

-4-

Module 7 - Switches/Sensors/Solenoids

4_1

Main Display Module GN BK

BK 18 BK 18 T° Rear Brake Oil Temperature Switch

Rear Brake

4_2 temperature Switch The top photo shows a brake oil temperature switch (arrow) located on an articulated truck. The temperature switch contacts are normally closed. When the engine is running and brake oil temperature is within the desired range determined by engineering, the contacts stay closed and complete the ground circuit. The switch opens once the brake oil temperature exceeds an acceptable limit, alerting the operator of the condition. This type of temperature switch can be tested using a digital multimeter on the volts or ohms scale. An excessive voltage drop across the terminals would indicate a defective switch.

Caterpillar: Confidential Yellow

SERV1877 - 03/10

Module 7 - Switches/Sensors/Solenoids

-5-

5_1

Main Display Module 2 Brake Oil Pressure

20

BK 16 PK 16

B

RD 16 BK 16 Brake Oil Pressure Switch

5_2 pressure Switch The top photo shows a brake oil pressure switch (arrow). The pressure-type switch contacts are normally open (engine not running/low oil pressure). When the engine is running and brake oil pressure is within the desired range, the contacts close and complete the ground circuit. If brake oil pressure drops to a level where the contacts open, the switch will interrupt the 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 as a low pressure event. This type of pressure switch can be tested using a digital multimeter on the volts or ohms scale. An excessive voltage drop across the terminals when adequate pressure is present would indicate a defective switch.

Caterpillar: Confidential Yellow

SERV1877 - 03/10

-6-

Module 7 - Switches/Sensors/Solenoids

6_1

Engine ECM Ground

2

Coolant Flow

18

BU 16 BK 16

BK 18 BK 18

Coolant Flow Switch

6_2 flow Switch The top photo shows an example of a coolant flow switch. The flow switch is a paddle type and is normally open, closing once there is sufficient fluid flow. If flow is restricted, the switch will interrupt the 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 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 (or when the paddle is hand actuated) would indicate a defective switch.

Caterpillar: Confidential Yellow

SERV1877 - 03/10

-7-

Module 7 - Switches/Sensors/Solenoids

7_1

Transmission ECM Sensor r Ret r

Parking Brake Op tc

J1

12

BN 16 PK 16

44

1 Parking Brake Switch

7_2 operator-activated Switch 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 to perform an action. In this application a parking brake switch (arrow) on an articulated truck sends a signal to the ECU when actuated by the operator. The ECU processes the 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 ohms scale. An excessive voltage drop or excessive resistance across the terminals while the switch is closed would indicate a defective switch.

Caterpillar: Confidential Yellow

SERV1877 - 03/10

-8-

Module 7 - Switches/Sensors/Solenoids

SENDERS / SENSORS (VARIABLE INPUT DEVICES) Parameter Monitored Speed

Sensor Makeup

Active or DMM Passive Measurements Passive (2 Wire) Volts / Hz / Ohms

Pickup Coil Hall Effect

Active (2/3/4 Wire) Volts / Hz / Duty Cycle

Variable Resistor

Passive (2 Wire) Volts / Ohms Active (3 Wire) Volts / Ohms Active (3 Wire) Volts / Hz / Duty Cycle

Temperature

Variable Resistor Variable Resistor

Pressure

Strain Gauge with Variable Resistor

Active (3 Wire)

Volts

Active (3 Wire)

Volts / Hz / Duty Cycle

Variable Resistor

Active (3 Wire)

Hall Effect

Active (3 Wire)

Magnetostrictive

Active (3 Wire)

Position

Fuel Level

Variable Resistor Ultrasonic

Volts / Hz / Duty Cycle

Passive (2 Wire) Volts / Ohms Active (4 Wire)

Volts / Hz / Duty Cycle 8_1

Sensors Sensors (variable input devices) can be classified in several ways as illustrated in the chart above. This chart shows the typical sensors and senders found on Cat engines and machines. The types of senders and sensors in this chart are classified by the parameter monitored. Other sensor characteristics include: • Sensor Makeup: Internal components that determine the type of signal produced. • Active or Passive: An active sensor receives power from the ECU or battery and must be powered to check operation. A passive sensor does not require power from the ECU and can be tested without power applied. • DMM Measurements: Type of electronic signals for a sensor that a digital multimeter can measure. NOTE: Most variable input devices are referred to as sensors. The fuel level input device with a variable resistor is normally referred to as a sender. All variable input devices will be referred to as sensors in this presentation.

Caterpillar: Confidential Yellow

SERV1877 - 03/10

-9-

Module 7 - Switches/Sensors/Solenoids

9_1

9_2

passive Sensors • Do not have to be powered in order to test. •

test off engine or machine (static test).

Passive sensors are typically two-wire sensors, with the exception of single-wire senders. Passive sensors do not require ECU or battery power in order to function and 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

Caterpillar: Confidential Yellow

SERV1877 - 03/10

-10-

Module 7 - Switches/Sensors/Solenoids

10_1

10_2 active Sensors Active sensors are typically three-wire sensors, but can be two- or four-wire. Active sensors require ECU or battery power in order to function and test. Active sensors fall into one of two categories: • Analog (top photo): A signal that varies smoothly over time and in proportion to the measured parameter. These signals are typically DC voltage. • Digital (bottom photo): Digital signals are usually associated with computerized electronic controls and measuring devices. The signal(s) will switch between two distinct levels, such as 0 to +10 Volts, or more simply stated as low and high. The internal electronics of a sensor determine 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

Caterpillar: Confidential Yellow

SERV1877 - 03/10

-11-

Module 7 - Switches/Sensors/Solenoids

DC Volts

+

0 Pressure (kPa) 11_1 analog Signals As previously mentioned, an analog signal is a signal that varies smoothly over time and in proportion to the measured parameter. Analog signals on Cat equipment are typically AC or DC voltage. The above illustration shows a DC analog signal trace of a pressure sensor. This type 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 in resistance, and thereby voltage, would be sensed by the ECU. NOTE: Analog sensors that have a DC output will have a typical operating range of 0.2 volts to 4.8 volts. Voltage ranges may be different, depending on application.

Caterpillar: Confidential Yellow

SERV1877 - 03/10

-12-

Module 7 - Switches/Sensors/Solenoids

One Cycle

0

Time

12_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, reverses polarity, rises to a peak negative value, and returns to zero. One positive and one negative 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.

Caterpillar: Confidential Yellow

SERV1877 - 03/10

-13-

Module 7 - Switches/Sensors/Solenoids

High

Two Distinct Amplitude Levels Low

13_1 Digital Signals • hall effect: varying requency, onstant Duty ycle • pwM: onstant requency, varying Duty ycle.

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 a specific 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 sensors operate using a current field and a piece of iron (gear tooth). When the gear tooth is introduced perpendicular to the current field, all of the electrons are forced to one side of the semiconductor (remember—like 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 Hall cell gives a “high” state. The “low” state 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 speed of the parameter being measured, and will typically have a constant duty cycle of 50%.

Caterpillar: Confidential Yellow

SERV1877 - 03/10

Module 7 - Switches/Sensors/Solenoids

-14-

PULSE WIDTH MODULATION +

On

ON (80%)

OFF (20%)

0 Off

One Period 14_1 The above illustration shows a PWM signal. A PWM signal is measured in duty cycle, which is defined as % time on (high) vs. % time off (low) for one pulse. In the example above, the signal is on (or high) for 80% of the pulse and off (or low) for 20% of the pulse. This would indicate a duty cycle of 80%. On Cat equipment, a position sensor would be a good example of a device that produces a PWM signal. A PWM signal has a constant frequency output and the duty cycle (percentage of time on versus time off) of the signal varies as conditions (rotary position) change. The output of the sensor is sent to an ECU where the signal is processed.

Caterpillar: Confidential Yellow

SERV1877 - 03/10

-15-

Module 7 - Switches/Sensors/Solenoids

15_1 Sensor ypes Sensors convert a physical parameter into an electronic signal. Electronic controls use this signal (input information) to monitor engine and machine conditions and determine appropriate output signals. Several different types of sensors provide this input information to the ECU. These include: • • • • •

Speed/Timing Temperature Pressure Position Fluid Level

Caterpillar: Confidential Yellow

SERV1877 - 03/10

Module 7 - Switches/Sensors/Solenoids

-16-

PASSIVE SPEED SENSORS - Two-Wire Sensor - Magnetic Pickup Coil

16_1

16_2

DMM MEASUREMENTS - Volts - Hz - Ohms 16_3 • basically a small generator. •

he Speed/ iming sensor provides signals to the

•

he signals are created as the timing wheel rotates past the sensor pickup.

.

• unique pattern of teeth indicates engine position (timing) to the each tooth is spaced apart the same number of degrees, with one extra tooth in the pattern. he detects this extra tooth and uses it as a reference point to determine timing.

16_4

A passive (two-wire) magnetic frequency-type sensor converts mechanical motion to an 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 of a gear tooth, generates an AC voltage in the coil. The AC voltage and the frequency of the AC signal is proportional to speed. Magnetic pickup sensors rely on the distance between the end of the pickup and the passing gear teeth to operate properly. Typically, when the pickup is installed, it is 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 may indicate that the sensor is too far away from the gear. It is important to check the specifications when installing these sensors to insure the proper spacing. Variable gap speed sensors are no longer used on new production equipment as fixed gap sensors are becoming more commonplace. Magnetic engine speed sensors may be used in pairs. One sensor is specifically designed for optimum performance at slower engine speeds which occur during cranking and when the engine first starts. The other sensor is designed for optimum performance at normal engine operating speeds. The mounting for the sensors differ from each other to keep them from being interchanged.

Caterpillar: Confidential Yellow

SERV1877 - 03/10

-17-

Module 7 - Switches/Sensors/Solenoids

Although the sensors have an optimum operating range, the ECU will use the signal from the remaining sensor as a backup in case of a failure. A magnetic pickup may be checked for both static and dynamic operation. With the pickup disconnected from the machine electrical harness, a resistance reading of the pickup coil (measured between pins) should indicate a coil resistance referenced in the specifications. The resistance value differs between pickup types, but an infinite resistance measurement would indicate an open coil, while a zero reading would indicate a shorted coil.

Caterpillar: Confidential Yellow

SERV1877 - 03/10

Module 7 - Switches/Sensors/Solenoids

-18-

ACTIVE SPEED SENSORS - Two, Three, or Four-Wire - Hall-Effect

18_1

18_2

SPEED SENSOR CIRCUIT Engine ECU

DMM MEASUREMENTS

J1

+V Sensor Supply

11

Sensor Ground Return

12

Engine Speed

62

OR 18 BR 18 YL 18

A B C

OR 18 BK 18 YL 18

+V Ground Signal Engine Speed Sensor

- Volts - Frequency

18_3 •

ower speed sensitivity; much more accurate than mag pickup type

•

all are three-wire ( ctive)

• Dependent on metal passing though a magnetic field •

requency (hz) varies

• Duty

18_4

Some Caterpillar electronic systems use a Hall-Effect sensor for detecting magnetic fields. The electronic transmission control uses this type of sensor to determine transmission output speed, and the electronic unit injection system uses this type of sensor 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 a digital signal to the ECU. The sensing element is extremely accurate because it is not speed dependent. The sensing element operates down to 0 rpm over a wide temperature operating range.

constant

• Square wave signal • voltage may change some but is a signal carrier, not the main signal to be measured

Caterpillar: Confidential Yellow

SERV1877 - 03/10

-19-

Module 7 - Switches/Sensors/Solenoids

19_1 The timing measurement function of a speed/timing sensor uses a change in the magnetic 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, direction of rotation, and rpm. The ECU counts each pulse and determines speed, memorizes the pattern (unique tooth pattern) of the pulses, and compares that pattern to a designed 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 below average (gap), the output will be low. If the signal is above average (tooth under cell), the output will be high.

Caterpillar: Confidential Yellow

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). The voltage drops of passive sensors and the voltage output of active analog sensors correlate 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 sensors can be checked with power OFF. Active digital temperature sensors also use a thermistor that is sensitive to changes in temperature. The circuitry inside the sensor body converts the analog output of the thermistor to a PWM signal, which is sent to the ECU.

Caterpillar: Confidential Yellow

SERV1877 - 03/10

-21-

Module 7 - Switches/Sensors/Solenoids

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 on Cat equipment are active (three-wire) analog sensors. Pressure sensors contain a strain gauge which changes resistance when a pressure is applied to it. The sensor circuitry detects this change in resistance and outputs a voltage in accordance with this resistance. The voltage output of a pressure sensor correlates to a specific pressure.

Caterpillar: Confidential Yellow

SERV1877 - 03/10

-22-

Module 7 - Switches/Sensors/Solenoids

22_1 position Sensors Position sensors convert mechanical component position into an electrical signal for the ECU. They are digital sensors which produce a PWM signal. The ECU reads this PWM signal and determines the position of the component, such as a throttle position. The above illustration depicts a lever or throttle position sensor. NOTE: The duty cycle output of a lever position sensor should be approximately 5% to 95% from stop to stop.

Caterpillar: Confidential Yellow

SERV1877 - 03/10

-23-

Module 7 - Switches/Sensors/Solenoids

23_1 Magnetostrictive position Sensor A magnetostrictive position sensor is shown in the above photo. This type of position sensor provides a PWM signal to the ECU, indicating cylinder position. In a magnetostrictive sensor, a pulse is induced in a specially-designed magnetostrictive wave guide by the momentary interaction of two magnetic fields. The magnetostrictive principle is defined as a change in resistance when a magnetic field is applied perpendicular to the current flow in a thin strip of ferrous material.

Caterpillar: Confidential Yellow

SERV1877 - 03/10

-24-

Module 7 - Switches/Sensors/Solenoids

24_1 In magnetostrictive sensors, a thin piece of wire (wave guide) is placed inside a protective tube. The wave guide transmits the input and output signals. An electronic current (input) pulse from the sensor electronic assembly creates a magnetic field around the protective tube. The magnetic field interacts with the position magnet’s magnetic field and causes the wave guide to twist. This twist is the return signal that is 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 elapsed time between the release of the electronic pulse and the arrival of the return signal (wave guide twist).

Caterpillar: Confidential Yellow

SERV1877 - 03/10

-25-

Module 7 - Switches/Sensors/Solenoids

25_1 level Sensors A level sender assembly is located in the top or side of a tank and measures the depth of fuel or oil in the tank. The depth of liquid in the tank determines the position of a float. This float will be attached 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. The sender is attached to the lever or rod, and changes resistances as the lever moves up and down, or as the rod rotates. This resistance is measured by the ECU or a mechanical gauge.

Caterpillar: Confidential Yellow

SERV1877 - 03/10

-26-

Module 7 - Switches/Sensors/Solenoids

26_1 Some Cat machines are equipped with an ultrasonic level sensor. This type of sensor is 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 an ultrasonic signal that travels up a guide tube in the tank. The signal is reflected off of a metal disk on the bottom of a float that rides on the fuel and is directed back to the sensor. The sensor measures the amount of time it takes for the signal to leave the sensor, reflect off the disk, and return to the sensor. The sensor has four contacts. The open or grounded status of contact three on the connector tells the ECU whether the sensor is installed in a deep tank or a shallow tank. Contact three should be open for a deep tank and grounded for a shallow tank. Troubleshooting procedures for the ultrasonic sensor would be the same as those used for other PWM sensors. The ultrasonic sensor must be installed in a fuel tank to be tested.

Caterpillar: Confidential Yellow

SERV1877 - 03/10

-27-

Module 7 - Switches/Sensors/Solenoids

27_1 Solenoids Many Caterpillar electronic control systems use solenoids to perform a control function. Some examples are shifting the transmission, raising an implement, fuel injection, etc.

•

lthough voltage is typically the measured parameter for troubleshooting, current performs the work.

Solenoids are electronic devices that work on the principle of an electrical current passing 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 of solenoid that is used is determined by the task that is to be performed. The transmission shift solenoids in the above photo divert oil when the spools are moved by 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 lower the duty cycle of the source voltage. As more current is needed, the duty cycle is increased.

•

simple compass may also be used to check for electrical functionality of a solenoid, as well as checking the resistance of the coil and comparing it to specifications.

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

Caterpillar: Confidential Yellow

SERV1877 - 03/10

Module 7 - Switches/Sensors/Solenoids

-28-

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) 28_1 PWM solenoids receive a varying PWM current from their respective ECU. A fault is recorded if the ECU senses the signal to the actuator solenoid as open, shorted to ground, or shorted to battery. •

he red dashed line shows the “baseline current versus pressure” for a solenoid valve used in the lectro- ydraulic Implement System. he area between the two solid lines is the acceptable tolerance bands for solenoid valve performance.

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

Caterpillar: Confidential Yellow