PMM has enlisted Darren Cotton, of AVC UK, to attend the full range of course modules on the Bosch Diagnostic Technician Programme over the coming months. On his third visit to Bosch, Darren took part in Module VSTD 9: Oscilloscope Operation & Signal Test Methods. Here’s how he got on.
The Oscilloscope Operation module covers two days and it takes a more detailed look at the course content of the previous module – (VSE 1) Essential Test Procedures. It is therefore beneficial if delegates have previously attended the Essential Test Procedures (VSE 1) as these two modules complement each other. This course focused on the set-up of an oscilloscope to measure a component, connection to a component, controls and adjustment, settings, waveform interpretation and analysis, test methods, and waveform display methods. We began the day with an overview of oscilloscopes, determining the variety of different tests that it is possible to undertake using this fantastic piece of kit. Firstly, we looked at the difference between analogue and digital signals, before considering what test applications digital multimeters are suitable for and discussing the limitations of a digital multimeter.
Our first practical task was comparing the digital multimeter against the oscilloscope and observing the visual difference on a live running engine. Back at the training room, the trainer went through the oscilloscope setup and explained the X and Y axes, sample rate, level and edge triggering and zoom functions. Each step was explained in detail, with the trainer making sure that each delegate understood the voltage parameter, voltage scale setting and time base setting for various common components. Basic waveform types, such as sine, step ramp, square and pulse were also explained.
This knowledge was then put into practice in the workshop. The group was split into two and we chose two components to view and stabilise. First up was a petrol injector – adjusting the voltage, with time to view and analyse the injector. An inductive crank sensor was connected, and the trainer made sure each delegate got involved, with the results and procedure discussed back in the training room. This brought us on to the importance of understanding the operation of the component we are measuring and how a sensor can modify or form a signal. Understanding a wiring diagram is also crucial, and this was covered in Bosch module ‘Essential test Procedures (VSE1)’, when making a connection. This section became a very interactive discussion within the groups, as the trainer asked the group questions, making sure we all understood the connection to the oscilloscope.
We stayed in the same groups and carried out various practical tasks in the workshop, including looking at camshaft sensor and crankshaft sensor dual display. We also used the trigger source to stabilise the waveform with an injector and primary ignition and performed starter current and volt drop testing. Having discussed the various waveforms we see with different components, we then moved into electrical noise and how we can eliminate outside noise using the oscilloscope’s signal filter feature, making sure we use this to observe the function format or pattern. The trainer showed the group the effects the filter has when using it in the correct manner and also when using it incorrectly.
This brought us into analysing waveforms, calculating the rise and fall time of a switching signal and the inclusion of measuring AC voltages, identifying the amplitude and peak values. A magnified example of an inductive ABS sensor was shown to the group, and the trainer showed us some measuring techniques with this waveform, calculating the peak and V effective (RMS) values, as well as ratio and frequency. We then scoped an inductive crankshaft sensor and used the calculation given in the training room.
The biggest benefit of this course was that it gave oscilloscope owners the knowledge and confidence to enable them to resurrect a versatile tool that for many had been resigned to a life in the toolbox. This module is ideal for those not using their oscilloscope enough due to lack of confidence or those wanting to improve their diagnostic procedures. You will realise how important an oscilloscope can be for certain tests and procedures. Three different oscilloscopes where used during the day, which gave us the opportunity to understand the set-up, learn and analyse different waveforms, and discover how we can interpret the signals we see.