Sensors, Digital Electronics, and Multiplexing - PowerPoint Presentation

Slide1

Sensors, Digital Electronics, and Multiplexing

Instructor Name: (Your Name)

11

CHAPTERSlide2

Learning Objectives

List the various types of sensors used on modern trucksExplain the difference between a digital and analog signalList the main logic gates and develop the truth table for bothDescribe the memory commonly used in an electronic moduleSlide3

Learning Objectives (continued)

List the four main types of electronic module inputsExplain the concept of a pull-up and pull-down resistor in an electronic module input circuitDiscuss the various forms of multiplexing used on modern truckSlide4

Sensors

Sensors convert physical properties to an electrical signalSensors are also known as transducers or sending unitsSensors are used by various electronic modules on modern trucksSlide5

ThermistorsOne of the most common sensors found on trucks

Two terminal temperature measuring sensor typically made of semiconductorsThe resistance between the two terminals changes proportionally with temperatureTypical temperature sensors have a negative temperature coefficientSlide6

RTD’s and Thermocouples

Resistance Temperature Detectors (RTD’s)- Two terminal temperature measuring sensorsConstructed of thin metal wire with a positive temperature coefficientThermocouples are constructed of two dissimilar metals such as iron and constantanThe junction of this combination of metals is know as a type J thermocoupleSlide7

RTD’s and Thermocouples (continued)

Both ends of the wires are welded to form a cold and hot junctionThe hot junction is where the temperature is being measuredThe cold junction is the reference with a known voltageThermocouples require amplification of the voltage producedSlide8

Potentiometers and RheostatsUsed to measure angle position of fuel gauges, accelerator pedal or other devices

Some diesel engines use an idle validation switch (IVS) to prevent unwanted acceleration in the event of a wiring problemSlide9

Variable Reluctance SensorVariable reluctance sensors are basically miniature AC

generatorsMade up of a coil wrapped around a permanent magnet and a low reluctance rotorThe rotor rotates past the tip of the sensorThe changing magnet field of the sensor induces a voltage in the coilThe output is AC voltage Slide10

Variable Reluctance Sensor

Figure 11-7 Variable reluctance sensor.Slide11

Variable Reluctance Sensor (continued)

As the rotor speeds up, the frequency increasesAs the rotor slows down, the frequency decreasesThe amplitude of the signal depends on the air gap and rotational speedEngine speed sensor and ABS wheel speed sensors use variable reluctance speed sensorsSlide12

Tech Tip

Proper wheel bearing adjustment is very important on trucks with ABS because a loose wheel bearing can cause the ABS sensor to be pushed away from the tone wheel, resulting in an inconsistent air gap between the sensor and the tone wheel. Just a small increase in the air gap between the tip of the sensor and the tone wheel will result in a large decrease in the voltage produced by the sensor.Slide13

Hall Effect SensorsCurrent is passed through a thin layer of semiconductor

When exposed to a magnetic field a voltage will be developed at the edges of the semiconductorThe level of voltage is directly proportional to the strength of the magnetic fieldThe voltage produced is referred to as a the Hall voltageSlide14

Hall Effect Principle

Figure 11-11 Hall effect principle.Slide15

Potentiometric Pressure Sensor

Figure 11-15 Potentiometric pressure sensor.Slide16

Strain Gauge SensorUsed to measure pressure in a chamber next to a known pressure

A flexible material with conductive material in a zigzag patternAs the material stretches the conductive material stretches and changes its resistanceThe change is typically converted to a voltage by a Wheatstone bridgeSlide17

Strain Gauge Sensor

Figure 11-16 Strain gauge resistance change due to deformation.Slide18

Wheatstone Bridge Used With a Strain Gauge

Figure 11-17 Wheatstone bridge used with the strain gauge (Rs).Slide19

Variable Capacitance MAP Sensor

Figure 11-18 Variable capacitance MAP sensor.Slide20

Piezoelectric Sensor

Figure 11-19 Piezoelectric pressure sensor.Slide21

Single Frequency Displayed as a Sine Waveform on Oscilloscope

Figure 11-20 Plucking a single guitar string results in a single frequency, displayed as a sine waveform on oscilloscope.Slide22

Analog Signal

Figure 11-22 Analog signal produced by microphone.Slide23

Figure 11-23 Analog signal divided into equaltime increments

Figure 11-24 Amplitude measures at each time interval

Analog Signal

(continued)Slide24

Figure 11-26 Re-created waveform fromnumerical information

Figure 11-27 Re-created waveform with increased sample time

Analog Signal

(continued)Slide25

Digital NumberingDigital information is stored in a binary numbering system

Only two numbers are used in the binary numbering system, 1 and 0Binary numbering works well with electronics because a switch has only two states, either off or onSlide26

The Number 9 Represented in Binary Format by Four Switches

Figure 11-30 Four switches used to represent the number 9 in binary format.Slide27

Digital Numbering (continued)

Each digit in a binary number is a bitA group of eight bits is one byteA CD is capable of storing 682 megabytes (682,000,000,) of information682 megabytes equals 682 million bytes containing 8 individual bits Computers store information on magnetic diskA binary 1 is stored in one format and a 0 is stored in another formatSlide28

Logic Gates

Digital electronics is mostly concerned with logic 0 and logic 1 valuesLogic is the use of correct or valid reasoning to come to a conclusionGates – Physical electronic components that are composed of transistors and other hardwareInputs to gates will be a 0 or 1Outputs form a gate will be a 0 or 1Because logic gates are logical they will always make the correct decisionSlide29

AND Gate With Truth Table

Figure 11-31 AND gate constructed of two switches in series.

Figure 11-33 Status of Switch A and Switch B truth table.Slide30

AND Gate Symbol and Truth Table

Figure 11-34 AND gate symbol and truth table.Slide31

OR Gate and Truth Table

Figure 11-35 OR gate constructed of two parallel switches.

Figure 11-36 OR gate symbol and truth table.Slide32

Figure 11-38 NAND gate and truth table.

Figure 11-39 NOR gate and truth table.Figure 11-37 NOT gate and truth table.

NOT, NAND and NOR GatesSlide33

MicroprocessorsIntegrated Circuit –

All components, such as transistors, resistors, and capacitors, are formed during the manufacturing process of the deviceIntegrated circuits are commonly known as chipsThe components of a chip are formed in layers of P-type and N-type materialProcessors or microprocessors

are the main component of computersSlide34

Integrated Circuit

Figure 11-40 Integrated circuit.Slide35

Microprocessors (continued)

Processors process information based on programming informationA microprocessor is an integrated circuit that may contain millions of transistorsMost modern trucks contain a variety of electronic modules that are microprocessor basedSlide36

Memory

Memory is a place where digital information is storedMemory is binary, 1’s and 0’sVolatile Memory – Lost or reset when power is lost or resetNon-Volatile Memory – Retained through power loss or disconnectRAM – Random access memoryEEPROM – Electronic, erasable, programmable, read only memory

Flash Memory – Large sections must be must be erased at the same timeSlide37

Inputs and Outputs

All inputs to a modern microprocessor are digitalAll outputs to a modern microprocessor are digitalSensors provide all of the inputs Sensor inputs must be converted from analog to digital signalsA circuit called an analog to digital (A/D) converter is used to convert from analog to digital signalsSlide38

Connecting a Variable Resistor to the Input Terminal

Figure 11-47 Connecting a variable resistor to the input terminal.Slide39

Sensor Changes to 2kΩ and Voltage at A/D Converter Increase to 8V

Figure 11-49 Sensor changes to 2kΩ, and voltage measured by A/D converter increases to 8V as voltage divides between pull-up resistor and sensor resistance.Slide40

Pulled Down InputA pull-down

resistor is a resistor between the input and groundTransfer Function – Microprocessor programming that converts input voltage to temperature, pressure, and other physical measurementsSlide41

Pulled Down Input

Figure 11-50 Pulled-down input.Slide42

Digital and Analog InputsFour basic types of

inputs; pulled-up, pulled-down, analog, and digitalAnalog signals must be converted to digitalElectronic module digital signals are typically switches with only two states: open or closedElectronic module digital signals may also be classified as pulled-up or pulled-downA pulled-down digital input may also be referred to as an active-high inputSlide43

Tech Tip

Wiring harness problems with three wire sensor reference voltage and ground (return) circuits can result in sensor measurement errors. High levels of circuit resistance caused by terminal corrosion can result in misdiagnosis and unnecessary component replacement.Slide44

Microprocessor Controlling Output

Figure 11-57 Microprocessor controlling one of its outputs based on its input values and programming instructions.Slide45

Multiplexing

Multiplexing is methods used to combine more than one channel of information into a single signal pathAnalog multiplexing would be a group of switches wired in parallel connected to a single inputTime-Division Multiplexing uses a single wire several sensors and microprocessor inputsSerial and USB ports found on a PC are forms of serial data communication using time division multiplexingSlide46

Multiplexing (continued)

Information sent out on the serial data link can be used by any device on the linkSAE defines the standard for digital information transmitted on the data linkSlide47

SAE J1587/J1708 Standard

SAE J1587 protocol have a bit transmission rate of 9600 bpsSAE J1708, standard that defines the hardware including the physical data wiring used with J1587, often referred to as ATA data linkMID Message Identifier – Transmitted first to identify major system or device sending informationPID Parameter Identifier – Indicates the specific informationSlide48

SAE J1939 Standard

J1939 replaces most J1578/1707 and J1922 serial communication standardJ1939 transmission rate is either 250k or 500kJ1939 requires specific twisted copper wire with special plastic insulationThe conductors are like two plates of a capacitor and the insulation acts as a dielectricThe impendence of J1939 cable is 120ΩCable that meets J1939/11 standards has a metal foil shieldSlide49

J1939/11 Shielded Cable

Figure 11-60 J1939/11 shielded cable.Slide50

Network TopologyTopology

refers to the manner the computer network is laid outJ1939 uses bus topology, a single communication line shared by several devicesThe single cable is called the backboneEach module is connected to the backbone by a cable less than 1meter called a stubTerminating Resistor – a 120Ω resistor across each end of the backboneSlide51

Oscilloscope Patterns

Figure 11-62 J1939 oscilloscope patterns with terminating resistors missing (upper) and present (lower).Slide52

J1939 Message Structure

Figure 11-63 J1939 message format.Slide53

Dual-Channel Oscilloscope Trace

Figure 11-65 Dual-channel oscilloscope trace of J1939 messages.Slide54

Figure 11-67 6-pin J1578/J1708 diagnosticconnector pin assignment

Figure 11-68 9-Pin diagnostic connector pin assignments

6-Pin and 9-Pin Diagnostic

ConnectorsSlide55

Summary

A modern truck may several different types of sensors used to measure temperature, pressure, speed, and position.A variable reluctance sensor is a small version of an A/C generator. These types of sensors are often used to measure a rotational speed such as an ABS wheel speed sensor.The Hall effect describes the generation of voltage in the presents of a magnetic field. The voltage that is generated is proportional to the magnetic field strength. Unlike electromagnetic induction, no magnetic lines of force have to be cut to generate this voltage.Slide56

Summary (continued)

An analog signal is a signal that can be any level within a range. A digital signal can only be one of two different values.Logic gates are hardware devices used to make a decision. There are several types of logic gates. A truth table describes the decision made by the logic gate to all possible inputs.Slide57

Summary (continued)

A microprocessor is an integrated circuit that contains thousands of logic gates. The microprocessor only accepts digital information and provides results in digital format. An analog to digital converter is used to convert real-world analog signals into the digital equivalent for use by the microprocessor. The main two categories of memory are volatile and non-volatile. Volatile is lost when power is disconnected from the device while non-volatile is retained through power disconnection.Slide58

Summary (continued)

The internal circuitry in an electronic module typically has pull-up or pull-down resistors.Electronic module inputs can be digital or analog types of inputs. These digital or analog inputs can be pulled-up or pulled-down.Multiplexing refers to methods used to combine more than one channel of information into a common signal path. Common forms of multiplexing used on modern trucks include analog and time-division multiplexing.Slide59

Summary (continued)

Serial data communication is a form of time-division multiplexing. An example of serial data communication is the J1939 data link.A controller area network (CAN) is a communication network without a master control device.