CartScope for testing
Published by CV Workshop, Autumn 2004
Rob Cooper goes hi-tech with the Pico oscilloscope
The Pico diagnostic kit includes the ADC-212/100 PC Oscilloscope; software (including a library of automotive waveforms and help files), and all the accessories required to measure electrical or electronic waveforms on a commercial vehicle. The AC/DC current clamp is rated at 2,000 Amps to match the high current draw of CV starter motors and to allow you to monitor charging currents or starter currents for relative compression testing. You also get all the necessary probes, pickups and clips, and a cigar lighter power lead.
With the oscilloscope you can check the CAN bus, injectors and fuel pumps, starter and charging circuits, ABS, crank, airflow sensors and glow plugs, and timer relays. It has a sampling rate of 100 MS/s (for capturing CAN bus signals) and a memory of 128 KB so that complex waveforms, such as cam and crank signals, can be recorded without sacrificing horizontal resolution.
we have a growing need for equipment that can help us quickly diagnose electronic faults
The PicoScope software converts the computer into an oscilloscope, spectrum analyser and a digital multimeter. Once it is loaded, the PC displays a drop-down menu with sub-menus for testing sensors, actuators, injectors and CAN bus signals. Once a particular test is selected, PicoScope automatically displays an example waveform and configures itself for optimum timebase, voltage scales and trigger settings. There are help files showing where to attach test probes and safety advice.
Learning curve
We were interested in the oscilloscope because we have a growing need for equipment that can help us quickly diagnose electronic faults. ABS sensors, for example, already cause numerous problems and more vehicle systems are being controlled electronically.
Testing with the oscilloscope was a bit of a learning curve. To start with, you have to familiarise yourself with the software on the computer, so you known basically how each test is done. This takes time, so to avoid being overwhelmed, the best way, I think, is to start with two or three tests and gradually increase the number of things you use it for.
Getting the kit setup in the workshop and the computer booted and ready-to-use is a definite must. Ideally the kit needs to be on a trolley. Otherwise if you are testing, say ABS sensors at the back of a trailer or coach, you have to carry the laptop, oscilloscope and probes the length of the vehicle, and make sure there is a convenient power outlet.
There's quite a lot of connections involved. Both the computer and the oscilloscope need a power feed and the oscilloscope connects to the computer via a printer-type cable. The probes plug into the oscilloscope. Unless you are checking something in the cab, the cigar lighter power lead for the oscilloscope is not long enough to stretch to all the points on truck and buses you want to check.
Using the laptop is quite straightforward. You just select the test you want to do. We didn’t want to risk our new computer out in the workshop, so we used an ancient laptop. If you were using the oscilloscope regularly, it would be worth investing in a newer computer. Although perfectly adequate, ours creaked along a bit, which would get frustrating.
The Software
The oscilloscope can capture the majority of signals on the truck
The PicoScope automotive diagnostic software interprets the signals captured by the oscilloscope. The oscilloscope can capture the majority of signals on the truck, including ignition, airflow, oxygen and ABS.
We concentrated on using it to help us check ABS sensors, which we've been having a lot of trouble with, and to do compression tests on misfiring engines.
The compression test helped us diagnose an engine starting problem by measuring the current draw. It did not tell us which cylinder was misfiring, but it did eliminate other possible reasons for the misfire.
When the ABS warning light comes on in the cab, diagnosing the problem is not straightforward. You can check the power feed to the ABS with a voltmeter, of course, but if the fault is intermittent, that doesn't help. It could be the sensor itself, a power problem or a connection fault.
The oscilloscope gives you enough information to pin-point the fault. To check whether ABS sensors are functioning, you simply clip the probes to the sensor and look at the screen. If you suspect the problem is a slipping pulse, the Pico kit will confirm it.
Waveform library
If you need more diagnosis help, there is a library of good and bad automotive waveforms on Pico’s website. They are organized into groups such as ABS, Air Flow, Alternator and so on. You can display multiple waveforms at the same time including those for starter current, injection units and crank sensors, and primary and secondary ignitions.
We didn’t actually get to use them, but including bad waveforms is a good idea, because if your actual waveform matches or is close, it’s likely to be the same faulty component.
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