AUTOMOTIVE OSCILLOSCOPE

The beginner’s guide

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Y-ax

is

X-axis

OSCILLOSCOPE SCREEN

The graphics shown on the monitor arecalled waveforms. This form of visualizationshows the change of voltage through time.The divisions marked on the horizontal x-axisallow for the time parameters to bemeasured, and the vertical y-axis allow forthe voltage (or other parameters such ascurrent or pressure) values to be measured.Oscilloscope can show the changes in oneor more input signal over time, allowing foramplitude and shape of the voltage to beaccounted, as well as making phase andfrequency measurements. If no electricalcurrent source is plugged into to theoscilloscope, the waveform is represented bya straight line. This line is called “zero” linebecause it represents a level correspondingto a 0V voltage at the input of theoscilloscope.

2/17All oscilloscopes have screens on which the waveform is shown.The typical oscilloscope screen is divided into equal spaces(divisions) which allow visual interpretation of the signal parameters.

Zero line

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Signal parameters control panel

THE THREE SYSTEMS

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Vertical: This is the attenuation oramplification of the signal. You can controlthe voltage range for each channelseparately.

Horizontal: This is the time base. Use thetime control to set the time baserepresented horizontally across thescreen.

Trigger: This is the triggering of theoscilloscope. Use the trigger level tostabilize a repeating signal, or to trigger ona single event.

An oscilloscope consists of three different systems – vertical system,horizontal system, and trigger system. The control panel of an oscilloscopeis divided into these three sections. When using an oscilloscope, you adjustsettings in these areas to accommodate an incoming signal.

http://www.autoditex.comVERTICAL SYSTEM AND CONTROLS

Common vertical controls are:

Position: Allows you to move the waveform up anddown so it’s exactly where you want it on the screen.

Range: This setting is a scaling factor that varies thesize of the waveform on the screen. Sets the maximumvoltage you can display on the screen.

AC/DC Coupling: If the DC coupling is used, thewaveform contains both AC and DC. When you needto see certain signals more closely, use the ACcoupling which removes the DC component of thesignal and allows you to zoom in tighter on thewaveform and measure small AC disturbances.

Invert: This feature is directly related to how the signalwill display on the screen. It allows you to display themeasured signal inverted on the screen.

Bipolar/Unipolar control: When set to Bipolar, bothpositive and negative values of the signal are shown.Unipolar - only the positive values are shown.

4/17Vertical controls are used to position and scale thewaveform vertically, set the input coupling and adjustother signal parameters.

AC coupling

DC coupling

Invert off (signal is not inverted)

Invert on (signal is inverted)

Zero volts

Zero volts

http://www.autoditex.comHORIZONTAL SYSTEM AND CONTROLS

5/17An oscilloscope’s horizontal system is most closely associated with itsacquisition of an input signal. Horizontal controls are used to positionand scale the waveform horizontally. Time base is the most importantsetting here.

Common horizontal controls are:

Time base: Lets you select the rate at which thewaveform is drawn across the screen. Thissetting is a scale factor. Changing the time baseenables you to look at longer and shorter timeintervals of the input signal.

Zoom: Some oscilloscopes may have specialhorizontal magnification settings that let youdisplay a magnified section of the waveform onthe screen.

Position: The horizontal position control movesthe waveform left and right to exactly where youwant it on the screen. In some oscilloscopes thePre-trigger setting acts like position control.

Zoom panel

Time base

http://www.autoditex.comTRIGGER SYSTEM AND CONTROLS

Trigger level: The trigger level and slope controls providethe basic trigger point definition and determine how awaveform is displayed. The trigger level line in the mainsignal screen designates the trigger level’s position.

Trigger edge: For edge triggering, you select the slope(positive or negative) and level, and the oscilloscopetriggers when your signal meets these conditions.

Pre-trigger: This program option gives the opportunity toobserve the measured signal shifted to the right on thehorizontal axis. Varying the horizontal position allows youto capture what a signal did before a trigger event, knownas pre-trigger viewing. Thus, it determines the length ofviewable signal before and after the trigger event.

Trigger type: When setting the trigger level, you shouldtake into consideration the constant input signal offset.Automatic triggering is an appropriate choice formeasuring periodically repeated signals. Single is usedmost often when the input signal is variable, but it’s notrepeating periodically in time. It’s applicable for a singlepulse on input signal that can appear randomly at theinput.

Trigger source: Allows you to choose from which inputchannel the triggering is being done.

6/17Triggering is one of the key functions within the oscilloscope. The triggerevent defines the point in time at which a repeating “window” of waveforminformation is stabilized for viewing. The moment, when the plotting of thenew screen starts, is called a “triggering” moment.

Trigger level

Trigger source is Channel A and we have signal only on it. Trigger type is Automatic!

Triggering on the “rising” edge

Pre-trigger

http://www.autoditex.comINPUT PROBES

To perform high voltage or current signals measurements such as:injectors, primary and secondary ignition and etc., you have toextend the input range of the oscilloscope with a suitable inputprobe.

Input probes

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You can choose from various input probes for eachinput channel separately. Common input probesare:

• Coil-on-Plug pick-up clamps;• Inductive pick-up clamps;• Voltage input attenuators;• AC/DC current clamps;• Pressure sensors and transducers

(Boost pressure sensor, Common rail pressure sensors).

With the Probe editor can edit or add your owncustom input probes to suit the measurement task.It’s very important that the input probes should atleast match, if not exceed the bandwidth of theoscilloscope.

http://www.autoditex.comAUTOMOTIVE PRESETS

Pre-sets automatically adjust the vertical scales, time base, thetrigger position and etc. for easy setup and operation. With the helpof the pre-sets you can make various sensor, ignition and injectormeasurements very easy. Preset editor allows you to add new andedit existing presets.

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Pre-sets are divided into different categories:

Sensors: Contains a rich set of engine sensorssuch as: MAF, lambda, CMP, CKP, ABS, MAP,TPS etc.

Injectors: Includes various petrol, diesel andLPG/CNG injectors.

Ignition: Covers all primary and secondaryignition types: coil-on-plug, direct, DIS,distributor etc.

Diesel: Includes common rail pressure sensorand injectors, turbo boost pressure sensor, fuelpressure and quantity valves etc.

Electrical system: Allows for battery andcharging tests as well as potentiometer andsolenoid measurements.

Communication: CAN bus measurements

Pre-sets

http://www.autoditex.comMEASUREMENT MARKERS - CURSORS

Cursors follow the mouse pointer and display the X and Y values at that point

Cursors are very useful when you to determine the exact value ofthe parameter on the Y axis, and the Time on the X axis. You canalso measure the difference in the X and Y values between twopoints.

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With the help of the Cursors, you can easymeasure the difference in the X and Yvalues between two points. Just click on thelocations of the graph that you want tomeasure and this places a temporary staticmarker on the selected point. When twomarkers are placed the absolute differencevalues are displayed in the measurementmarker label. ΔT is the absolute timedifference, ΔV is the absolute difference inthe quantity being measured by the activechannel. This functionality is not availablewhile running a measurement.

http://www.autoditex.comMEASUREMENT MARKERS – 720 DEGREE SCALE

720 degree cursors make the diagnosis easier allowing you tomake a measurement corresponding to an operating cycle of thefour-stroke cycle engine that requires two revolutions (720°) of thecrankshaft.

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Pressing the 720 degree button enables adraggable, expandable 720 degrees scale whichcan be expanded by left-clicking and dragging itsarrows. You can add any number of markers onthe screen and these markers can be draggedover the scale by clicking and dragging themarkers or their text. While the zoom is enabled,720-degree line position, its size, or the positionof the already added markers, cannot bechanged. This functionality is not available whilerunning a measurement.In the example on the left, the in-cylindercompression waveform is shown. You can clearlysee the 720 degree markers as well as thepressure and vacuum values. See the In-cylinderpressure testing example waveform at slide 16.

Atmospheric pressure

http://www.autoditex.comEXAMPLE WAVEFORM – CRANKSHAFT POSITION SENSOR

Crankshaft Position Sensor (CKP) is an electromagnetic sensor bythe help of which the fuel injection system makes synchronization ofthe fuel injectors operation and the ignition system.

Crankshaft Position Sensor (CKP) sendssignal for the speed and the position of thecrankshaft to the onboard controller (ECU).This signal is a series of repetitive electricalvoltage impulses, generated by the sensorwhen the crankshaft is rotating. Based onthese impulses, the ECU controls the fuelinjectors and the ignition system.On the left a typical waveform from aCrankshaft Position Sensor - inductive type isshown. Notice the AC bipolar voltage (bothpositive and negative). In this case the voltagerange is set to ±5V and the time base is set to200mS.

Positive voltage

Negative voltageZe

ro v

oltsPositive voltage

around 7V

Negative voltage around 1V

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http://www.autoditex.comEXAMPLE WAVEFORM – COMMON RAIL PIEZO INJECTOR

Common Rail injectors make possible fine electronic control over the fuel injectiontime and quantity, and the higher pressure provides better fuel atomization.Injectors can be fired in rapidly several times during the injection cycle. With thisprecise control over injector firings, smaller, staggered quantities of fuel deliverycan be timed over the course of the power stroke to promote complete andaccurate combustion.

Piezo injectors make diesel engines even moreclean, more economic, more powerful and morequiet. Some advanced common rail fuelsystems perform as many as five injections perstroke. These injectors work by passingelectrical current through a stack of Piezocrystals, causing them to expand. Theexpansion and contraction of the crystalsdisplaces the fuel within the injector, causingthe needle valve to open and close extremelyquickly.

This a typical waveform from a Common Railpiezo injector. During the opening of the piezoinjector, a positive current up to 12 amperes isgenerated. Injector must be closed manuallyand this causes the negative current values!Notice the high positive voltage (up to 140V)and note that in this case a 10:1 or 20:1attenuator must be connected to the voltageinput due to the high input voltage!

Negative current up to -12A

Zero volts and amps

Positive voltage around 140V

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Positive current up to 12A

http://www.autoditex.comEXAMPLE WAVEFORM – PRIMARY IGNITION

Coil oscillations

Firing line

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Burn time

The coil is the heart of the ignition system. There areactually two coils (primary and secondary) of wire woundabout an iron core. These coils are insulated from eachother and the whole assembly is enclosed in an oil-filledcase.

Ignition systems can be divided into the following types:

• Distributor Ignition System;

• Direct Ignition System - individual coil for each cylinder;

• Coil-on-Plug (COP) type;

• DIS-Wasted Spark Ignition.

Primary voltage can rise up to 300-400V so a 20:1 inputattenuator must be connected to the input to collect theprimary ignition waveform. Ignition waveform containsspecific points and sections each of them talking aboutthe ignition system individual components condition:spark plugs, high tension wires, ignition coil(s) etc.

Ignition system is a system for igniting a air-fuel mixture. Ignition systemis divided into two electrical circuits - the primary and secondary circuits.The primary circuit carries low voltage. This circuit operates only onbattery current and is controlled by the breaker points and the ignitionswitch.

Pre-trigger

http://www.autoditex.comEXAMPLE WAVEFORM – SECONDARY COIL-ON-PLUG IGNITION

Elements of the secondary ignition pattern:

Dwell angle (dwell period): This is the angle on whichthe crankshaft rotates from the beginning of accumulationof energy in the primary winding of the ignition coil untiloccurring of the spark in the spark plug.

Advance angle: This is angle on which the crankshaft isrotating at the moment when the spark arises untilreaching the relevant cylinder at the top dead center.

Drilling voltage (firing line): This is the value of voltagein the secondary circuit at the time of appearance of thespark and it’s the maximum voltage in the secondarycircuit. It directly depends on the distance between theelectrodes of spark plugs and the mixture in the cylinders.Typical value of this tension is between 7 kV and 12 kV.

Voltage combustion of the mixture (spark kV): Thepoint when the actual spark across the gap starts to takeplace. This illustrates the energy required to actuallyinitiate the spark and keep it going.

Burn Time (spark duration): Spark combustion length isnormally 1.5mS to 2mS. The "spark line" is the actual timethe spark is moving across the plug gap.

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Cylinder 1 Cylinder 2 Cylinder 3 Cylinder 4

Coil oscillations

Firing line

Burn time

Three basic components make up the secondary circuit of the ignitionsystem - the ignition coil, the distributor, and the spark plug. SecondaryCoil-on-Plug (COP) systems use one individual coil for each spark plug.Each coil is located directly on top of its spark plug and does not useany external spark plug wires. Each coil pack also has an independentprimary circuit which must be tested individually.

Spark Kv point

Dwell period

http://www.autoditex.comEXAMPLE WAVEFORM – CAN BUS

The CAN controller is connected to all thecomponents on the network via these two wires.Each network node has a unique identifier. AllECUs on the bus are effectively in parallel andthat’s why all the nodes see all of the data, all ofthe time. A node only responds when it detectsits own identifier.

CAN bus is a message-based protocol, designedspecifically for automotive applications but nowalso used in other areas such as aerospace,industrial automation and medical equipment.

It was specially developed for fast serial dataexchange between electronic controllers in motorvehicles. It connects the individual systems andsensors as an alternative to conventional multi-wire looms. It allows automotive components tocommunicate on a single or dual-wire networkeddata bus up to 1Mbps. CAN bus is one of fiveprotocols used in the OBD-II vehicle diagnosticsstandard.

15/17The CAN bus (Controller Area Network) is an automotive busdeveloped by Bosch, allowing microcontrollers and devices tocommunicate with each other within a vehicle without a hostcomputer. CAN bus uses two dedicated wires for communication.The wires are called CAN high and CAN low.

ACKNOWLEDGE BIT

ACKNOWLEDGE BIT

CAN low

CAN high

http://www.autoditex.comEXAMPLE WAVEFORM – IN-CYLINDER PRESSURE TESTING

By the position of the characteristic points and sections of thecylinder pressure waveform of a gasoline engine, you candetermine the proper synchronization between the crankshaft andthe gas-distributor shafts. Measurement and comparison of theabsolute cylinder pressure values at certain characteristic points,allows determining the condition of the cylinder seals. You candetect serious mechanical defects in the tested cylinder with thehelp of the cylinder pressure waveform.

To perform a cylinder compression test a pressure transducershould be screwed up in place of the spark plug of anycylinder. You can view the cylinder pressure waveform in realtime on your oscilloscope. You can also measure AC, turboand fuel pressures. Cylinder pressure waveform allows you todetermine:

• The real ignition advance angle by the ratio of TDC to the high voltage pulse.

• The condition of the engine mechanics by observing the pressure difference before and after the compression (approx.).

• The correct position of the exhaust camshaft by observing the opening angle of the exhaust valve.

• The correct position of the intake camshaft by observing the valve overlap position and the opening of the intake valve.

• The condition of the exhaust valve guide sleeve by the shape of the waveform.

• The permeability of the exhaust system by the pressure value at the exhaust phase in the area of the waveform between 180ᴼ and 360ᴼ.

• The presence and the vacuum value in the intake manifold.• The presence of a gap in the timing belt by the difference in

the angles of overlapping of the valves from one frame of the waveform to the next frame.

Pressure is around the atmospheric

Highest pressure value (indicates compression)

In these zones we have a vacuum

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This is the atmospheric pressure

http://www.autoditex.comCARSCOPE FAMILY OSCILLOSCOPES

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CarScope family oscilloscopes are used for all measurements and instructions in this guide!CarScope program has a pre-defined sensor-specific measuring settings and you just have toselect the sensor, actuator or ignition circuit that’s going to be tested and the softwareautomatically loads the required settings and gives you full details of how to connectthe device, a pattern waveform and general technical information for the component or thesystem under test. Plus, LAN are 4 channels and Viso is 2 channels. All have engine analyzerand ignition capabilities for use with any vehicle. You can choose from many automotiveaccessories to suit your measurement task. All CarScope devices are free from USBconnectivity problems, common for most automotive oscilloscopes.

CarScope Plus is a high quality four channel automotive digital storage oscilloscope withenhanced speeds especially built for the automotive industry. When you want speed, accuracyand reliability then this is the smart choice. CarScope Plus uses LAN Ethernet connection andhas a high stability trigger system made of four independent hardware-based circuits. This isan affordable way to diagnose today’s high-tech vehicles. CarScope Plus is an enhancedversion of CarScope LAN!

CarScope LAN is а system specially designed as a reliable and easy to use tool primarily forautomobile service professionals. It consists of a PC program and a hardware device.CarScope LAN uses LAN Ethernet connection to connect to the PC.

CarScope Viso is a professional automotive component tester with touch screen color displayand it’s the single solution to all your engine analysis needs. The Viso automotive digitalstorage oscilloscope provides you with affordable performance in a compact design. It’spacked with useful features such as: USB connectivity, component tester with built-in presetconfigurations, primary and secondary ignition capabilities with presets, dual graphingvoltmeter, frequency counter and context sensitive help menu. The Viso oscilloscope helps youget more done, in less time.