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1. Test Bench ou would be hard pressed to find an automotive technician who has not used an oscil loscope to diagnose a particular problem Most technicians either own a scope or are planning to buy one in the near future But with so many dif ferent scopes available to the automotive repair industry how will you select the scope that best suits your needs If you are not familiar with using an oscilloscope you may want to select a scope that has preset default setting for most of the items you will use it for Preset default settings save time while also helping the technician to become familiar with volt age time and trigger setting It is equally important that the default settings be adjustable and that the adjustments can be saved for later references Do you need a hand held scope that will handle ignition If so then the scope that you choose should have adequate primary and secondary igni tion capability for most vehicle ignition systems Remember that all of the digital storage oscillo scopes presently marketed for automotive use do not have the same ignition capabilities 20 First Impressions Of The Perception This month we turn our attention to the OTC Perception a digital storage oscilloscope DSO Additional versions of the Perception are sold by MAC Tools MAC Wave Enhanced MATCO Tools Reality and Cornwell Tools Tech Trace Other than slight differences in appearance such as the color of the out2. Actuator menu will open the scope display with the voltage time trigger level and slope preset to view the most com mon peak and hold injector patterns Although the settings are preset they can be adjusted to better view the waveform More importantly the adjust ments can be saved as the new default settings Sampling An Injector Waveform The time setting has been preset to 20 mS mean ing that the scope s display is 20 mS wide Figure 5 To decrease the time setting press the DOWN arrow key until the trigger symbol is highlighted Then press the RIGHT arrow key until the 20 mS time set ting is highlighted Press the Change Settings DOWN 21 The Perception arrow key once to decrease the time setting to 10 mS This will widen the injector waveform in respect to the scope s display because less time is displayed The waveform on a 10 mS scale will appear twice as wide as on a 20 mS scale Figure 6 The available time adjustment range is from 1 mS per display to two seconds per display Changing the voltage setting is just as easy as adjusting the time setting Use the UP arrow key to highlight the volt setting located at the upper left side of the dis play Then use the Change Setting key to increase or decrease the voltage setting per display Increasing the voltage setting decreases the vertical size of the waveform On the other hand decreasing the volts per display will increase the height of the wavefor
3. also changes the time per display for Channel 2 In most cases this would not be a problem however the time per display must be set differently when dual tracing an injector wave form and O sensor waveform in order to view an accurate picture of both Normally the injector waveform is viewed at approximately 10 20 mS per display An O sensor waveform cycles much slower making it difficult to examine in the same time frame Graphing the O sensor signal voltage gives a much clearer picture of the rich lean PCM control by allowing the time set ting of the graphing display to differ from the time setting of the scope display July 1998 IMPORT SERVICE Scoping The Ignition The Perception will display both primary and secondary igni tion waveforms Some DSOs have signal interference prob lems when connected to view a primary ignition waveform which will stall the vehicle by pulling the coil negative low The Perception has an internal resistance which prohibits the scope from affecting the negative side of the coil Selecting Ignition from the Component Tests menu will bring up the Ignition menu which con sists of PIP SPOUT DI Primary DI Secondary EI DIS Pri and EI DIS Sec Selecting DI Primary from the Ignition menu will automatically set up the scope s time per dis play volts per display trigger and slope to view the primary ignition waveform of a Distributor type ignition system Selecting EI DIS Pri wi
4. ease in the voltage drop across the injector The trigger voltage level would normally need to be adjusted so the scope will not redraw the trace each time the voltage drops to 5 volts during the high fre quency hold time The Trigger Auto Level OFF ON function located under the Advanced Setup menu eliminates the need to make such trigger adjustments When the Trigger Auto Level is turned ON the scope has the unique ability to recognize the normal characteristics of the waveform and automatically setting the trigger level so that the waveform will appear at the center of the screen While the Trigger Auto Level is turn ON it is almost impossible to set the trigger voltage level incorrectly Turning the Trigger Auto Level OFF however will set up the scope so that the trigger level must be set manually Some DMMs have the ability to measure saturated switch type injector pulse width but will read incor rectly when measuring peak and hold injector pulse width The peak time of a peak and hold injector waveform does not change This amount of time is physically required to open the injector Only the hold time varies to control fuel In most cases a DMM will measure only the peak time and does not recognize the hold time as part of the injector pulse width The hold time starts at the rising edge of the first spike and ends at the rising edge of the last spike The PCM will vary the width of the hold time only The true pulse width is the comb
5. ined peak and hold time Figure 8 Multimeter The Perception has the ability to simultaneously display both the injector pulse width in mS and the wavetorm By highlighting the Meter measurements 24 4 gt os E Dual Tracing Injector and O Sensor Figure 10 Secondary Ignition Testing g located in the center of the screen above the scope display the Change Settings keys can be used to select from several types of measurements The Meter measurement selections consist of INJOT Injector On Time INJPK Injector Peak Voltage IGNBT Ignition Burn Time IGNPV Ignition Peak Voltage IGNBV Ignition Burn Voltage DWELL RMP DUTY Duty Cycle WIDTH PERIOD FREQ Frequency PK PK Voltage Peak to Peak NEG PK Negative Peak Voltage POS PK Positive Peak voltage ACAVG AC Average Voltage and DCAVG DC Average Voltage Up to four types of measurements can be viewed simultane ously with the scope display Graphing Capabilities Because of its graphing and multimeter functions the Perception is not limited to displaying wave forms Although nothing replaces an oscilloscope display I found the graphing capability of the Perception to be particularly useful when dual trac ing an injector waveform and an O sensor waveform Figure 9 In the Dual Display mode the scope s time per display is adjustable but the time for both displays must be set the same Adjusting the time per display for Channel 1
6. ll set up the scope to view a Distributorless Ignition system s primary ignition waveform Time voltage and trigger adjustments can be made to better view the waveform To view a secondary ignition waveform the Capacitive Probe must be connected to the Perception s Channel 1 port and ground port Because of the wide air gap between the rotor and dis tributor cap on DI systems clamp ing the probe around a spark plug wire will result in an insufficient signal Clamping the probe around the coil wire Figure 10 provides an inductive signal that is more sta ble for viewing secondary ignition Advanced Settings The Advanced Setup menu F igure 11a C on next page allows the user to manually configure most of the Perception s operating char acteristics Here the user can cou ple Channel 1 and or Channel 2 to AC or DC select the probe type to be used Volt Amp Ignition Temp set the trigger mode to Auto or Wait and turn Trigger level ON or OFF IMPORT SERVICE July 1998 Using the DOWN arrow key to scroll to the bottom of the menu will bring up the next Advanced Setup menu page which allows the user to adjust the Horizontal Trigger Position turn the Beeper On or Off set the mV per A for the low current Amp Probe select the Temp Scale display F or C select number of cylinders for dwell measure ments select dwell in degrees or percent duty cycle select number of sparks per shaft rota tion and selec
7. m making it appear taller in respect to the dis play Figure 7 Figure 6 Changing Waveform Time Base Trigger level voltage and slope are preset as well Adjusting the trigger level voltage tells the scope at what point to start draw ing the trace The slope can be set to positive or negative which tells the scope to start the trace on a rising or falling voltage of the waveform The preset trigger for viewing a peak and hold injector pattern is 5 volts nega tive slope This tells the scope to start the trace when the injector driver pulls the negative side of the injector s winding from bat tery voltage to 5 volts This only happens once per injector pulse unless it is a Bosch type peak and hold injector which cycles above and below 5 volts at a high frequency during the hold time Normally a peak and hold injector is pulled to ground approximately 0 50 mV volts for a fixed amount of time to allow the injector to open During this time peak time the voltage drop across the injector is equal to battery charging voltage The PCM then decreases the volt age drop across the injector while holding the pintle off its Figure 7 Changing Voltage Scale seat using less current than was initially required to lift it The Bosch type peak and hold injector is cycled during current limiting rather than a direct linear The Perception Figure 8 Figure 9 17 Peak And Hold Injector Waveform decr
8. side case or the shape of the buttons on the control panel all versions of the tool func tion exactly the same The Perception is equipped with everything needed to view automotive waveforms including e Six AA Alkaline batteries e Test Leads e AC Adapter e Ignition Capacitive Probe for secondary ignition e Carrying Case e Scope User Manual and Video Refer to the photo that begins this article for a look at the Perception s accessories July 1998 IMPORT SERVICE Figure 1 Perception Controls Using The Perception In this section we ll give you a quick tour of the Perception s basic controls Before you purchase this or any other DSO we would suggest that you do a hands on trial of the scope under actual working conditions in your shop All DSOs have their own personalities and there s no better way to decide whether that personality is compatible with yours than to hold the scope in your own two hands Located just below the Perception screen are the four way arrow keys used to move the highlighter selector Figure 1 Enter and Exit buttons are locat ed on both the left and the right of the arrow keys which allows the user to access the controls with either hand Below the four way arrow keys are the two Change Setting keys for changing the settings of the scope graph and multimeter Located to the left of the Change Setting keys are the Light button back light on off Help button and Power button The
9. t the memory locations for glitch capture Using the DOWN arrow key to scroll to the bottom of the second page will bring up the final Advanced Setup page which consists of Sleep Mode On Off and Contrast adjustments The Perception Figure 11a Figure 11b Advanced Setup Menu 1 Glitch Capture By far the Perception s most unique feature is its abil ity to capture a waveform glitch Using a technology called anomaly triggering the Glitch Capture has the ability to recognize the normal characteristics of a particular waveform and store the abnormal section of the waveform in the event of a glitch This means the Perception has the intelligence to recognize the normal characteristics of waveforms that change in both amplitude and frequency such as a wheel speed sensor waveform and trigger on drop outs and abnormal spikes Upgrades Future upgrades and added options for the Perception will be accomplished via a PC through a modem This can be accomplished through a Bulletin Board System connection while the Perception is connected to a serial port via a RS232 cable The Flash EEPROM software can also be downloaded from the company web page then used to Flash Program the EEPROM of the tool through a RS232 cable A waveform database consisting of 75 000 vehicle setups is being developed for the Perception and will work in conjunction with OTC s GTI software This will allow the user to download and store waveforms from
10. the Perception to a PC If you would like to receive more information Circle No 126 for the OTC Perception Circle No 127 for the Mac Wave Enhanced Circle No 128 for the Matco Tools Reality or Circle No 129 for the Cornwell Tech Trace on the Reader Service Card m By Mitch Belew 26 Advanced Setup Menu 2 Figure 11c Advanced Setup Menu 3 The Perception IMPORT SERVICE July 1998
11. two controls located to the right of the Change Setting keys are the Hold button and the Glitch button Turning on the Perception will automatically bring up the Main Menu consisting of Component Tests Single Display Dual Display Advanced Setup and Glossary Figure 2 Selecting Single Display or Dual Display will automatically put you into the manual scope mode Selecting Component Tests opens the Component Tests menu which con sists of Sensors Actuators Electrical and Ignition Selecting an item from the Component Tests Menu Figure 3 will open additional submenus For instance selecting Actuators will open an Actuator Tests menu Figure 4 consisting of Injector PFI MFI saturated switch type Injector TBI peak and hold type Injector PNP Mixture Ctrl Sol EGR Ctrl Sol IAC Step Motor IAC Motor IAC Sol Trans Shift Sol Turbo Boost Sol and Glow Plug Amps All submenu items originating from the Component Tests menu have preset default time voltage and trigger settings meaning that selecting an item from either the IMPORT SERVICE July 1998 Figure 2 Figure 3 Main Menu Component Menu Sensors Actuators Electrical or Ignition menu will automatically set the scope s voltage time trigger level and slope for optimum acquisition and viewing of the waveform for that particular device Figure 5 p Figure 4 1 lags al a nr E Actuator Tests Menu TBI Waveform Selecting Injector TBI from the
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