The above figure graphically shows the voltage curve of a functioning injector valve which is activated for approx. 2ms. Much more important however, is, in the course of this text, the small red cross on the left in the rising voltage. It concerns a trigger-point, whose proper setting is essential for a correctly indicated oscilloscope picture.

When 'triggering' one determines the conditions under which parts of a constantly changing signal should be described on the monitor. Using todays oscilloscopes with memory, the previous area can be described by a cross placed not quite on the far left, earlier this area remained empty.

When should the representation on the monitor begin? For this purpose, one can select the rising or the falling flank. Should a certain Y-value fall short or should it be exceeded? The value is precisely set by shifting the cross upwards or downwards. In the above picture the value of about 10 V, which should be reached with a rising flank, has obviously been placed. Normally one uses 75% of the peak value. With the setting 'falling flank', the whole curve would move 2 ms to the left. Should the cross be placed much further upwards, above approx. 12 V, the whole picture starts to scroll horizontally, because the trigger-point is no longer relevant for this curve.

Oscilloscopes for electronic technicians have also other types of triggers, for the workshop however, these are sufficient. Since apart from the triggering, also the correct choice of scale is time consuming for the unpractised, there are certain siignals, like the one shown above, which can be pre-selected. The course and the maximum values for various vehicles does not differ greatly. Thus, triggering, scale division and the legend are preset. One can also save and store ones own settings as a basis for further measurments. 04/08