dso function generator exercise

Digital Storage Oscilloscope (DSO)Hands-On Exercise

Self-Study Workbook 970193

Channe

Channe

el A

el B

Pulse Width

Perio

HighState

od

e

Low State

Leading Edge

Trailing Edge

Audi of America, LLCService TrainingPrinted in U.S.A.Printed 7/2010Course Number 970193

2010 Audi of America, LLC

All rights reserved. Information contained in this manual is based on the latest information available at the time of printing and is subject to the copyright and other intellectual property rights of Audi of America, LLC., its af liated companies and its licensors. All rights are reserved to make changes at any time without notice. No part of this document may be reproduced, stored in a retrieval system, or transmitted in any form or by any means, electronic, mechanical, photocopying, recording or otherwise, nor may these materials be modi ed or reposted to other sites without the prior expressed written permission of the publisher.

All requests for permission to copy and redistribute information should be referred to Audi of America, LLC.

Always check Technical Bulletins and the latest electronic repair literature for information that may supersede any information included in this booklet.

iTable of Contents

Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1

Exercise . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2

Automotive Electrical Signals Glossary . . . . . . . . . . . . . .10

Analyzing Automotive Electrical Signals . . . . . . . . . . . . .15

Automotive Electrical Sensors and Actuators . . . . . . . .16

Knowledge Assessment . . . . . . . . . . . . . . . . . . . . . . . . . . .19

The Self-Study Workbook provides introductory information regarding the design and function of new models, automotive components or technologies.

The Self-Study Workbook is not a Repair Manual!All values given are intended as a guideline only.Refer to the software version valid at the time of publication.

For maintenance and repair work, always refer to the current technical literature.

Reference Note

!

1Due to the increasing complexity of todays electronic systems in Audi vehicles, using a digital storage oscilloscope (DSO) to accurately diagnose electrical concerns has become a necessity. It is important that every Audi Technician thoroughly understand the capabilities and use of the DSO.

This workbook will help reinforce and test the knowledge you gained in the DSO web-based training course (970194). Through the use of a signal generator, you will have the opportunity to practice and apply your new DSO knowledge in real world situations. This workbook will guide you through the process.

It is recommended that you print out the workbook so that you can ll in the DSO readings requested throughout the exercise.This workbook will also be a helpful referencefor the future.

To complete the following exercise, you willneed a VAS Scan Tool with Test Instruments function, and an Elenco Electronics FG-500 1Mhz Function Generator.

The Elenco Electronics FG-500 1Mhz Function Generator can be purchased online from one of the following sources (you may be able to locate additional online sources as well):

http://techedu.com

http://www.tequipment.net

http://electronickits.com

To order the correct FG-500, type FG-500 in the search eld of any of the sites listed above. There are two versions available, the FG-500 (factory assembled version) and the FG-500K(kit version).

It is recommended that you purchase theFG-500 assembled version and not the FG-500K kit version because the latter requires soldering and assembly.

Once you have the VAS Scan Tool and theFG-500, you are ready to perform the exercise. However, if you have a thorough working understanding of the DSO, feel free to go straight to the workbook assessment onthe CRC.

Please note that the DSO web-based training course (970194) must be completed beforeyou attempt the assessment for this workbook. Be sure to complete the workbook assessment (970193B) to receive credit for these combined courses.

Introduction

NoteDo not try to rush through this exercise! Remember that this is a learning process. Try to see how accurately you can complete it, not how quickly. Take your time and make sure that you understand each step before proceeding.!

2To start, con gure the FG-500 as follows:1.

Make sure that the FG-500 has a good battery

Turn the Course Frequency knob to 10 Turn the Find Adj. Frequency knob to the left (counter-clockwise) until it stops

Make sure that the ON/OFF switch is in the OFF position. It will be turned ON in a later step

The Sine/Triangle switch will not be used in this exercise, so it can remain in either position

Start the VAS Scan Tool DSO by selecting:2.

Test Instruments Go To DSO

Connect the DSO to the Function Generator 3. as follows:

Connect the DSO 1 red lead to the yellow banana jack labeled Square Wave

Connect the DSO 1 black lead to the black banana jack labeled GND

Exercise

34. The rst waveform is a relatively slow (low frequency) signal. To properly view this waveform, Draw Mode must be used:

Select the Measuring Mode button Select the Draw Mode button Deselect the Measuring Mode button

5. Turn the Function Generator ON. You should see a waveform that is similar to the one at right. If the DSO screen does not look like this:

Make sure that the battery in the FG-500 is OK

Go back to the beginning of the exercise and read each step carefully

There are two things wrong with this waveform:

The waveform is displaying above the top of the screen (arrow). A waveform should never display above or below the top or bottom of the screen

The individual pulses of the waveform are so compressed that they are unreadable

To remedy these problems, the DSO must be con gured to display the waveform properly, which you will do in the next steps.

46. To make the waveform t the screen, the voltage division must be changed:

Select Channel A Since the waveform needs to be smaller, the voltage division must be made larger

Select the voltage division arrow until the Channel A voltage division displays 5 V/Div.

Deselect Channel A The waveform now ts the screen

7. To make the individual pulses of the waveform visible, the time division must be changed:

Since the pulses need to be wider, the time division must be smaller

Select the Time/Div. arrow until the time division displays 0.5 s/Div.

8. Take a few moments to experiment with how the voltage and time division buttons alter the appearance of the waveform:

Change the voltage division and then the time division up and down while observing the changes to the waveform

When nished, return the voltage and time division to their previous settings

5 V/Div.

0.5 s/Div.

59. Notice that the height of the waveform only occupies about 25% of the screen. While this is perfectly acceptable, it may be possible to make it taller. To do this, the zero point of the waveform must be changed

Select the Channel A button Move the slider down to the rst division above the bottom of the screen as shown at right

Press the voltage division arrow until the voltage division for Channel A displays 2 V/Div.

Deselect the Channel A button

10. The waveform is now looking good, but there is still one problem: The green Channel B waveform (DSO 2) is in the middle of our waveform, which could make it hard to read. Two things can be done to remedy this:

Move Channel B to the bottom of the screen (similar to how Channel A was moved previously)

Turn Channel B OFF, which removes it entirely

11. Lets do both:

Select Channel B To move Channel B, move the slider to the bottom of the screen, as shown at right. Now the Channel B waveform does not interfere with the Channel A waveform

To turn Channel B OFF entirely, select the Channel button, then select OFF. This removes the waveform, and may be the best choice for our next step, measuring pulse width

Deselect the Channel button Deselect the Channel B button

612. Before proceeding, lets review the names for the parts of a waveform. Knowing the parts of a waveform will help you perform the following steps.

Please refer to the Automotive Electrical Signals Glossary for more information

13. Now measure the amplitude of the high and low signal states:

Select the Freeze Frame button Select the Cursor 1 button Tap the screen to move the cursor to approximately the middle of one of the high state pulses as shown at right

The high state amplitude can be found in the box labeled Channel A Amplitude. Write the amplitude below:

_________________________________________

Tap the screen to move the cursor to the middle of one of the low state pulses

The low state amplitude can now be found in the box labeled Channel A Amplitude. Write the amplitude below:

_________________________________________

Ignore the number in the box labeled Time

Deselect the Freeze Frame button

Pulse Width

Perio

HighState

od

e

Low State

Leading Edge

Trailing Edge

CCursor 1

714. Next, measure the pulse width of the signal:

Select the Freeze Frame button Select the Cursor 1 button Move the Cursor 1 to the left of the leading edge of one of the pulses and then use the Cursor button to move it to the right until the box labeled Channel A Amplitude starts to increase. It is important to see where the amplitude begins to increase. This is the point where the signal turns ON

Ignore the number in the box labeled Time

Go to the next step

15. Select Cursor 2:

Move Cursor 2 to the left of the trailing edge of the same pulse and then use the Cursor button to move it to the right until the voltage display labeled Amplitude Diff. A starts to decrease. It is important to see where the amplitude begins to drop. This is the point where the signal turns OFF

The box labeled Time Difference is the pulse width of the signal. Read the pulse width and write it below:

_________________________________________

Cursoor 1

Cursor 2

816. While the previous waveform had a low frequency, the next waveform has a high frequency. Start by resetting the DSO to its default values. The easiest way to do this is to exit and restart the DSO

Select Go To Select Exit Select Text Instruments and start the DSO Leave the DSO 1 leads in the same positions as the previous steps

17. To con gure the Function Generator:

Turn the Coarse Frequency knob to 100K. Leave the other knobs and switches in the same positions as they were in the previous steps

18. The DSO should look like the screen shown at right. To con gure the DSO to display this waveform:

First move or remove the Channel B waveform from the screen using one of the methods shown previously

Even though this is a high frequency pulsed signal, all you will see is a at line for Channel A. This is because the default time and voltage settings are too slow to display the individual pulses of the waveform, which can make it dif cult to set the proper time and voltage divisions.

You can experiment to achieve the correct settings manually, but there is an easier way. When trying to con gure the DSO for an unknown signal, use the Auto Setup mode.

Select the Measuring Mode button Select the Auto Setup button. It takes a few seconds for Auto Setup to run

When Auto Setup has nished, the measuring mode changes to Auto Level

Channe

Channe

el A

el B

919. Your screen should look like the screen shown at right. Now it is time to practice the skills you learned previously:

Change the voltage division to make the waveform appear as large as possible in the screen. You need to move the zero point in the waveform so that the waveform does not display above or below the top or bottom of the screen

After completing the previous step, write the nal voltage division of the waveform below:

_________________________________________

Change the time division to display at least 5 readable pulses (that are not compressed) on the screen. Write the time division below:

_________________________________________

Measure the high state amplitude and write it below:

_________________________________________

Measure the low state amplitude and write it below:

_________________________________________

Measure the pulse width of the waveform and write it below:

_________________________________________

20. Turn the FG-500 OFF

Congratulations! You have completed the DSO Hands-On Exercise. Please remember to take the online assessment on the CRC, course #970193B.

10

Automotive Electrical Signals Glossary

Amplitude: The voltage level of a signal above or below zero volts. The signal in the example at left has an amplitude of 2V.

Analog Signal: An electrical signal whose amplitude can be measured at an in nite number of positions along the waveform.

Digital Signal: An electrical signal with an instantaneous change in amplitude (called a pulse) from low to high and high to low. Since the change in state is instantaneous, the amplitude can only be measured in two positions, high or low.

The pulse shown at left is a positive pulse, because the normal state of the waveform is low and the pulse goes high. However, with a negative pulse, the normal state of the waveform is high and the pulse goes low.

Sine Wave: An analog signal where the current reverses direction at regular intervals, also called alternating current (AC). In automotive applications, sine waves are produced by either the alternator (unrecti ed) or inductive sensors (such as the RPM sensor).

11


Square Wave: A digital signal that continuously alternates between ON and OFF. A true square wave is ON and OFF for an equal length of time. A variation of the square wave is the rectangular wave, which is ON and OFF for an unequal length of time, but is usually still called a square wave.

Period: The time required for a signal to complete one cycle. It can be measured in seconds (s), milliseconds (ms), or microseconds (s).

Frequency: The number of times a signal repeats in one second (cycles per second), measured in Hertz (Hz). The example at left has a frequency of 3Hz.

The frequency of a signal can be xed or variable. Any sensor that measures a rotating component (such as the camshaft position sensor) generates a variable frequency signal.

Pulse Width: The time that a signal remains ON during one period. It can be measured in seconds (s), milliseconds (ms), or microseconds (s).

Pulse width is similar to duty cycle, except duty cycle is measured in percent (%) instead of time. See Duty Cycle.

12


Waveform: The graphic representation of an electrical signal as displayed on an oscilloscope screen. While waveform is the preferred name, it is also called a trace or a pattern.

Duty Cycle: The percentage (%) of time a signal remains ON during one period.

Duty cycle is similar to pulse width, except pulse width is measured in time instead of percent. See Pulse Width.

Duty cycle is calculated by dividing the pulse width (s, ms, or s) by the period (s, ms, or s), and then multiplying the result by 100. For example, a signal with a 50 ms pulse width and a 100 ms period has a 50% duty cycle.

% Duty Cycle =

Pulse Width X 100

Period

Pulse Width Modulation (PWM): A signal that varies the pulse width of a signal. It is also called variable duty cycle.

13


Leading Edge: When viewing a waveform, the change in vertical height at the beginning of the signal. It is also called the rising edge or positive edge.

Trailing Edge: When viewing a waveform, the decrease in vertical height at the end of a signal. It is also called the falling edge or negative edge.

14


Networked Signals: A signal that consists of a sequence of coded pulses (sequence of event signals) used to broadcast data between a network of control modules. The CAN, LIN, and FlexRay buses are networked signals.

Sawtooth Wave: A signal in which the amplitude instanteously rises and then ramps down, giving the appearance of a sawtooth.

NoteThe following lists provide general information on sensors, actuators, and their signals. They are not intended to account for every sensor and actuator in the vehicle, and applications include, but are not limited to, those listed.!

15

Analyzing Automotive Electrical Signals

Three Factors

Three factors affect automotive signals:

Amplitude

Frequency

Sequence of Events

Amplitude: ON/OFF, analog, pulse width modulated, and duty cycle signals are characterized by the rate of change in amplitude, or the time the signal remains in the high or low state.

When used in sensor applications, the amplitude or pulse width (duty cycle) of a signal is varied to supply data to a control module. Thermistors, potentiometers, Hall switches and pressure sensors are commonly used in this way.

Frequency: Square and sine wave signals are examples of signals that are characterized by changes in frequency (the number of times they repeat themselves per second).

In sensor applications, Hall and inductive sensors are used to provide rotational data such as RPM, CMP, and wheel speed sensors.

Sequence of Events: Sequence of event signals are characterized by a series of pulses that can be compared to messages sent by Morse code.

By altering the sequence of the pulses, an almost in nite number of coded messages can be quickly and accurately transmitted between different control modules. Networked signals that are used by the CAN, LIN, and FlexRay buses are examples of sequence of event signals.

16

Automotive Electrical Sensors and Actuators

Analog Sensors

Thermistor: A two wire sensor that utilizes a resistor whose resistance varies with temperature. The thermistors used in most automotive applications have a Negative Temperature Coef cient (NTC), where the resistance of the thermistor decreases as the temperature increases. In a Positive Temperature Coef cient (PTC) thermistor, the resistance of the thermistor increases as the temperature increases.

NTC thermistors are commonly used as temperature sensors. The temperature value is not obtained by reading the sensor resistance directly, but instead by placing a reference voltage (usually ve volts) and ground across the sensor and then reading the resulting voltage drop.

Potentiometer: A three wire variable resistor that is used as a voltage divider. A reference voltage (usually ve volts or battery voltage) and ground are placed across a resistance element.

A wiper is moved across the element to produce an in nitely variable voltage signal from zero up to the reference voltage, which is measured on the third wire. In automotive applications, potentiometers are commonly used as position sensors for motors, or for measuring throttle plate position.

Inductive Sensor: A two wire sensor that measures the rotation of a shaft. Unlike other sensors, this sensor does not have an external power supply. Instead, it contains a permanent magnet that creates a magnetic eld which collapses and expands when a sensor wheel is rotated through it, generating an AC sine wave signal.

The frequency of this signal varies with changes in the RPM of the sensor wheel. Many crankshaft position (RPM) sensors and older ABS wheel speed sensors are inductive sensors.

Knock Sensor: A two wire sensor that is used to measure spark knock in an engine. This sensor uses a crystal material that generates an AC voltage when mechanical stress is applied to it (piezoelectric effect) when spark knock occurs. During installation, a knock sensor must be properly torqued to read spark knock correctly.

Digital Sensors

Hall Sensors and Switches: A two or three wire electronic sensor that produces a variable frequency square wave signal. Power and ground are supplied to a Hall Effect Transistor which is located in a magnetic eld generated by a permanent magnet.

As the magnet eld is altered by moving the magnet in relation to the transistor, or by moving a shutter wheel through the magnetic eld, the reference voltage is alternately pulled high or low, resulting in a square wave signal. Hall sensors are often used to measure the position of rotating components such as camshaft position sensors.

Pressure Sensor: A three wire electronic sensor that converts pressure measurements into an electrical signal. Power and ground are supplied to a pressure sensing device, which then produces a PWM or analog signal relative to the measured pressure.

The third wire transmits the PWM signal to the control module. While the majority of automotive pressure sensors fall into this category, some older types of sensors may use potentiometers to read pressure.

17

Automotive Electrical Sensors and Actuators

Actuators

Solenoid: A two wire electromechanical device used to control the ow of liquids, gases, or the operation of mechanical components. To operate the solenoid, an ON/OFF, PWM, or variable frequency signal (commonly a switched ground) is supplied to a winding inside the solenoid, which in turn generates a magnetic eld that moves a plunger.

Depending on the design of the solenoid, the plunger may be normally open, or normally closed in its rest state. A fuel injector is an example of a solenoid.

When the signal to the solenoid is switched OFF and the magnetic eld around the winding collapses, the winding produces a phenomenon called inductive kick.

Inductive kick is a high voltage pulse that is injected back into the control circuit, and is similar in principal to the pulse produced by an ignition coil, although the voltage is much lower (generally around 30 to 60 volts).

Relay: An electromechanical switch that uses a low current input signal to control a high current output signal. It contains a winding that is used to magnetically move a set of points (switch), similar to the operation of a solenoid. When an ON/OFF signal is supplied to the winding, a magnetic eld is generated which changes the position of the switch.

Depending on the design of the relay, the switch may be normally open, or normally closed, in its rest state. The most common type of relay is a four wire relay, which uses two wires for the control circuit and two wires for the switched circuit.

Relays that use more than four wires are usually variations of this design, usually containing multiple control and switched circuits. If a relay contains logic circuits, it is generally considered a control module, although it may still be called a relay.

Like solenoids, relays also produce an inductive kick. Automotive relays may have a built-in suppression circuit consisting of a resistor or diode placed parallel to the winding.

Motor: A device that converts electrical energy into rotational motion. On late model vehicles, the speed of most motors is controlled using PWM circuits.

If a motor has low output, checking the motor amperage can determine if the problem is electrical or mechanical. Increasing the electrical resistance in a motor circuit will decrease the amperage in the circuit, while increasing the mechanical load on the motor shaft will increase the amperage in the circuit.

The direction of motor rotation can be changed by reversing the polarity of the signals to the motor.

Notes

18

Knowledge Assessment

19

An online Knowledge Assessment (exam) is available for this Self-Study Workbook.

The Knowledge Assessment is required for Certi cation.

You can nd this Knowledge Assessment at:

www.accessaudi.com

From the accessaudi.com Homepage: Click on the ACADEMY tab Click on the Academy Site link Click on the CRC/Certi cation link Click on Course Catalog and select 970193B DSO Hands-On Exercise Self-Study

Workbook Assessment

For assistance call:

Audi Academy

Certi cation Resource Center (CRC)

1-877-283-4562

(8:00 a.m. to 8:00 p.m. EST)

Or you may send an email to:

[email protected]

Thank you for reading this Self-Study Workbook and taking the assessment.

dso function generator exercise

Documents