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1、Electrical Circuit Diagnosis Course 6236 1 Oscilloscope An oscilloscope displays voltage changes over time Use an oscilloscope to view analog and digital signals when required during circuit diagnosis Fig 6 01 TL623f600c An understanding of digital and analog signals will help you choose appropriate
2、 test equipment and troubleshoot effectively Automotive circuits use two types of signals INPUT provides information about operating conditions switches sensors OUTPUT causes an electrical or electronic device to operate lamps LEDs relays motors Input and output signals can be either digital or anal
3、og depending on the application Electronic Control Units ECUs typically receive process and generate both analog and digital signals Section 6 Introduction to Electronic Signals Input and Output Signals Section 6 6 2TOYOTA Technical Training A signal that represents a continuously variable voltage i
4、s an analog signal Variable resistors A throttle position sensor incorporates a continuously variable resistor to generate an analog signal Variable resistor changes the sensor s internal resistance with the position of the throttle The voltage produced by the sensor is also continuously variable it
5、 is an analog signal The signal can be any value from 0 through battery voltage A fuel gauge sender is another device that uses variable resistance to send an analog signal Oscilloscope Display of Analog and Digital Signals Input and output signals can be either analog or digital Fig 6 02 TL623f602c
6、 Analog Signals Introduction to Electrical Symbols Electrical Circuit Diagnosis Course 6236 3 Temperature and position sensors These sensors vary internal resistance in response to temperature or position The signal is a varying voltage analog type Analog Signals This sensor is a variable resistor t
7、hat generates an analog signal Fig 6 03 TL623f603c Section 6 6 4TOYOTA Technical Training A signal that represents just two voltage levels is a digital signal A digital signal has only two states The signal is not continuously variable The two states can be expressed in various ways High Low ON OFF
8、1 0 In a typical automotive electronic circuit a digital signal is either 0 volts or 5 volts Example 1 A switch is a simple device that generates a digital signal Switch open 0 volts also Low or OFF Switch closed 5 volts also High or ON Electronic Control Units ECUs can derive or provide information
9、 through these characteristics of a digital signal Signal state ON or OFF Signal frequency how many times per second the signal state change from high to low Signal duration how long a signal stays ON or OFF Duty cycle the percentage of time ON versus time OFF Digital Signal Power Steering Pressure
10、Switch A switch is an example of a digital signal producing device The output is either on or off and produces either a high or low voltage Fig 6 04 TL623f604c Digital Signals Introduction to Electrical Symbols Electrical Circuit Diagnosis Course 6236 5 Electronic Control Units monitor inputs proces
11、s input signals and generate output signals Inputs Switches and sensors send input signals to ECUs These signals tell the ECU what is happening in the systems it is controlling Input signals provide the ECU with information about operating conditions and driver commands Outputs ECUs are used to cont
12、rol various systems in the vehicle Engine Automatic transmission Climate control Cruise control Anti lock braking traction control and VSC Accessory systems One type of ECU is an Engine Control Module ECM A typical ECM has these input signals Water temperature Air fuel ratio oxygen sensor Crankshaft
13、 position Camshaft position Throttle position Mass air flow An ECM processes the information from the sensors and generates output commands to devices and systems that control engine operation Ignition Fuel Electronic Control Units Section 6 6 6TOYOTA Technical Training Engine Control System An ECM
14、processes information from sensors and generates output commands to control engine operation Fig 6 05 TL623f605c Introduction to Electrical Symbols Electrical Circuit Diagnosis Course 6236 7 Divider Electronic Control Units monitor some sensors using a voltage divider circuit A voltage divider circu
15、it is typically used to generate a voltage that is different from the supply battery voltage ECU Input Voltage ECU s monitor some sensors with voltage divider circuits Fig 6 06 TL623f606c ECU Input Voltage Divider Section 6 6 8TOYOTA Technical Training How an Electronic Control Unit processes an inp
16、ut depends on the signal type Digital signals Digital signals are in a form that ECUs can process directly Analog signals ECUs typically convert an analog signal to a digital signal before processing the information For example an analog wheel speed sensor signal is converted to ON and OFF pulses for processing by the ABS ECU Look up tables ECUs process most input signals using look up tables A look up table is a set of instructions one for each possible condition the ECU may see For example if
