Automotive Lab Scope Diagnostics
Unlike the voltmeter, with an oscilloscope you can not only see the mean values of the voltage in the circuits measured, but also the change and shape of that voltage through time.
All oscilloscopes have screens on which the waveform is shown. The screen can be a cathode-ray tube type, a liquid crystal display (LCD) or in the form of a computer program. The typical oscilloscope screen is divided into equal spaces (divisions) which allow to visually interpreting the parameters of the signal.
The graphics shown on the monitor are called waveforms. Usually oscilloscopes show only waveforms of the voltage. This form of visualization shows the change of voltage through time.
The divisions marked on the horizontal(x) axis allow for the time parameters to be measured, and the vertical(y) axis allow for the voltage values to be measured.
2. What purposes have oscilloscopes in automotive diagnostics?
The oscilloscope helps us find the problem quick and easy. Often the problem hasn’t recorded an error code (DTC) in the corresponding ECU, a DTC that can be read with a code reader. Usually a DTC is recorded when there is a broken cable or a cable has short circuited to a positive or negative supply. But when a detector or a mechanism has stopped working in some mid position, there is no error recorded. In this case, as when you need to find the reason that caused an error to be recorded – the automobile oscilloscope is your most needed instrument.
With the increase of sensors, actuators and wiring diagrams built in the modern automobiles, the automobile oscilloscope is an instrument which diagnoses irregularities in the automobile faster and easier. The oscilloscope is a irreplaceable tool, when you have to observe output signals from inductive sensors, whose output signals form a impulse sequence, slow-changing analog signals, primary and secondary ignition circuits, intake manifold absolute pressure, starter current waveforms, charging currents and etc.
3. What types of oscilloscopes are there?
The ones with a cathode-ray tube screens. They show detailed graphics, and can usually show high frequencies, but are not suited for observing short processes repeated through a long time interval or relatively slow processes like the ones in an automobile.
Digital storage oscilloscope
The observed result from the digital storage oscilloscope is almost identical to the analog, but the signal shown on the DSO can be “frozen still” on the screen, saved on the PC’s hard drive, and used later, or printed. Further more only the current “screen” shown on the monitor can be saved, and a sequence of many screens can later be opened and observed through time as an animation. Any screen saved in the working file can be printed.
There are two kinds of digital oscilloscopes: independent which are external device, and PC oscilloscopes. The PC-based oscilloscopes are a new type of "oscilloscope" that consists of a specialized signal acquisition board, which can be an external USB or Parallel port device, or an internal add-on PCI or ISA card.
One, dual and multiple-trace oscilloscopes
Depending on the number of measuring inputs, both analog and digital oscilloscopes can be divided into 3 types: one-trace, dual-trace and multiple-trace oscilloscopes.
Universal and specialized oscilloscopes
Depending on their purpose oscilloscopes are divided into 2 groups – universal and specialized. In automobile repair, an ignition analyzer is used to show the spark waveforms for each cylinder. In this way the specialized automobile oscilloscopes are also used for testing injectors, ABS, O2 sensor, quick compression tests, fuel pump, CAN Bus and much more. The Motortester is a specialized automobile oscilloscope.
4. What’s the universal oscilloscope?
The universal oscilloscope is an electronic measuring device used only for observing electrical voltage through time. The screen of the oscilloscope shows the changes in one or more input signals over time in an X-Y display, allowing for the amplitude and shape of the voltage to be accounted, as well as making phase and frequency measurements of the signal.
In order for the oscilloscope to observe other physical parameters, as well as observing voltages outside its original ranges different types of additional attachments and transformers that convert the given input into voltage are used.
5. What is the difference between a motortester and a lab scope?
The motortester is one kind of specialized oscilloscope used for auto diagnostics.
The main difference between a motortester and a universal oscilloscope is that the motortester is capable of visualizing short-timed processes like the ignition spark process. This process is exceptionally fast, and the period of repeat of the ignition of sparks in time is many times greater than the time the spark itself exists. This is easily observable when testing the engine in idle speed, when the majority of the measurements are conducted.
For example: if we observe the ignition cycle of a 4 cylinder gasoline engine, and an ignition spark that lasts around 2ms, at 800 RPM, the time period between sparks on a single cylinder would be 150ms. What this means is that the ‘length’ of the spark would account for around 2% of the actual work cycle, and therefore the burning of the sparks will be seen as very thin lines on the screen of the oscilloscope, and no information about the phases of the ignition would be seen. Because of this many diagnostics are forced to increase the RPM of the engine thus shortening the ignition cycle thus ‘saturating’ the waveform of the cycle.
The motortester shows all the cylinders simultaneously, and allows for detailed observation of the time period that includes: dwell period, drilling voltage, burn time and turbulence of voltage.
Most motortesters can show the cylinders graphs next to each other, or under one another, excluding the long time periods between sparks, this method is also known as “parade”.
Another distinctive feature of the motortester is that it can show its time divisions on its horizontal (x) axis in milliseconds as well as in degrees – up to 720 degrees.
6. Features that allow PC-based oscilloscopes to be used in auto diagnostics.
Lower cost than a stand-alone oscilloscope, assuming the user already owns a PC.
Easy exporting of data to standard PC software such as spreadsheets and word processors.
The software of the device can be directly installed on a PC and upgraded via CD or directly download from the Internet without having to send the device back to its manufacturer.
Use of the PC's disc storage functions, which cost a lot extra when added to a self-contained oscilloscope.
PCs typically have large high-resolution color displays which can be easier to read than the smaller displays found on conventional scopes. Color can be utilized to differentiate waveforms.
PC-based USB oscilloscope get their power supply from a USB port, so no external source is required.
The USB oscilloscope as any other USB device can be turned on/off without having to turn off/on the computer.