Opel Astra, Zafira

Since 1998 of release

Repair and car operation

Application of an oscillograph for supervision of workers of a control system

The general information

Digital multimeters perfectly approach for check of the electric chains which are in a static condition, and also for fixing of slow changes of traced parametres. At carrying out of the dynamic checks which are carried out on the working engine, and also at revealing of the reasons of sporadic failures by absolutely irreplaceable tool there is an oscillograph.

Some oscillographs allow to keep oscillograms in the built in module of memory with the subsequent conclusion of results to the press or their swapping to the carrier of the personal computer already in stationary conditions.

The oscillograph allows to observe periodic signals and to measure pressure, frequency, width (duration) of rectangular impulses, and also levels of slowly varying pressure. The oscillograph can be used at performance of following procedures:

• Revealings of failures of astable character;
• Checks of results of the made corrections;
• Monitoring of activity of a ljambda-probe of a control system of the engine equipped каталитическим with the converter;
• The analysis of the signals developed by a ljambda-probe which deviation of parametres from norm is unconditional the certificate of infringement of serviceability of functioning of a control system as a whole. On the other hand, correctness of the form of impulses given out by the gauge can serve as a reliable guarantee of absence of infringements in a control system.

Reliability and simplicity of operation of modern oscillographs do not demand any special special knowledge and experience from the operator. Interpretation of the received information can be easily made by elementary visual comparison of the oscillograms removed during check with the time dependences resulted more low typical for various gauges and actuation mechanisms of automobile control systems.

Parametres of periodic signals

The general information

Characteristics of any periodic signal

Each signal removed by means of an oscillograph (see an illustration of the Characteristic of any periodic signal), can be described by means of the following key parametres:

• Amplitude: the Difference of the maximum and minimum pressure () a signal within the period;
• The period: Duration of a cycle of a signal (мс);
• Frequency: Quantity of cycles in a second (Hz);
• Width: Duration of a rectangular impulse (мс, мкс);
• Porosity: the Relation of the period of repetition to width (in foreign terminology return is applied porosity parametre named a running cycle, expressed in %);
• The signal form: Sequence of rectangular impulses, individual emissions, a sinusoid, sawtooth impulses, etc.

Usually characteristics of the faulty device strongly differ from reference that allows the skilled operator easily and quickly to reveal the refused component by the analysis of the corresponding oscillogram.

Direct current signals

Unique performance data of such signals is pressure.

Direct current signals are developed by the devices presented more low.

Alternating current signals

The basic characteristics of the given signals are the amplitude, frequency and the signal form.

The frequency-modulated signals (ЧМ)

Performance data of the frequency-modulated signals are the amplitude, frequency, the form of a signal and width of periodic impulses.

Sources ЧМ of signals are the devices presented more low.

The signals modulated on width of an impulse (ШИМ)

Performance data of signals of pulse-width modulation (ШИМ) are the amplitude, frequency, the form of a signal and porosity of periodic impulses.

Sources of signals ШИМ are presented below the device.

The coded sequence of rectangular impulses

Performance data are the amplitude, frequency and the form of sequence of separate impulses.

This sort of signals are generated by the module of memory of self-diagnostics ECM of a control system of the engine.

The amplitude and the signal form remain the constants, the written down value will stand out until memory of the module will not be cleared.

Interpretation of oscillograms

The form of a signal given out by an oscillograph depends on set of various factors and can change appreciably. In a kind told before to start replacement of a suspected component in case of discrepancy of the form of the removed diagnostic signal with the reference oscillogram, it is necessary to analyse the received result carefully.

Digital signal

Analogue signal

Pressure

Zero level of a reference signal cannot be considered as absolute basic value, - "zero" of a real signal, depending on concrete parametres of a checked chain, it can appear shifted concerning reference ([1] - the Digital signal see an illustration) within a certain admissible range.

The full amplitude of a signal depends on pressure of a food of a checked contour and also can vary in certain limits concerning reference value ([3] - the Digital signal see an illustration and [2] - the Analog signal see an illustration).

In chains of a direct current pressure of a signal is limited to pressure of a food. As an example it is possible to result a chain of system of stabilisation of turns of idling (IAC) which alarm pressure does not change in any way with change of turns of the engine.

In chains of an alternating current the amplitude of a signal already unequivocally depends on frequency of operation of a source of a signal so, the amplitude of the signal which is given out by the gauge of position of a cranked shaft (CKP) will increase with increase of turns of the engine.

In a kind told if the amplitude of a signal removed by means of an oscillograph appears excessively low or high (up to trimming of top levels), it is enough to switch only a working range of the device, having passed to a corresponding scale of measurement.

At check of the equipment of chains with electromagnetic management (for example, system IAC) at food switching-off pressure throws ([4] - the Digital signal see an illustration) which at the analysis of results of measurement can be ignored easy can be observed.

It is not necessary to worry also at occurrence of such deformations of the oscillogram, as скашивание the bottom part of forward front of rectangular impulses ([5] - the Digital signal see an illustration) if, of course, the fact выполаживания front is not a sign of infringement of serviceability of functioning of a checked component.

Frequency

Frequency of repetition of alarm impulses depends on working frequency of a source of signals.

The form of a removed signal can be edited and led to a kind convenient for the analysis by switching on an oscillograph of scale of time development of the image.

As already it was told above, for signal reduction to a legible kind it is enough to switch scale of time development of an oscillograph.

In certain cases the signal oscillogram appears developed mirror concerning reference dependence that speaks реверсивностью polarity of connection of a corresponding element and, in the absence of an interdiction for change of polarity of connection, can be ignored at the analysis.

Typical signals of components of control systems of the engine

Modern oscillographs are usually equipped only by two alarm wires together with a set various щупов, allowing to carry out device connection practically to any device.

The red wire is connected to a positive pole of an oscillograph and usually connected to the plug of the electronic module of management (ECM). The black wire should be connected to reliably earthed point (weight).

Fuel injectors

Management of structure of an air-fuel mix in modern automobile electronic systems of injection of fuel is carried out by timely updating of duration of opening of electromagnetic valves of injectors.

Often on the oscillogram it is possible to observe also a series of the short pulsations following directly behind the initiating negative rectangular impulse and supporting the electromagnetic valve of an injector abroach, and also the sharp positive throw of pressure accompanying the moment of closing of the valve.

Serviceability of functioning ECM can be checked easily up by means of an oscillograph by visual supervision of changes of the form of an operating signal at a variation of working parametres of the engine. So, duration of impulses at проворачивании the engine on single turns should be a little above, than at unit work on low turns. Increase of turns of the engine should be accompanied by respective increase in time of stay of injectors abroach. The given dependence is especially well shown at opening throttle заслонки by short pressing a gas pedal.

At cold start the engine requires some enrichment of an air-fuel mix that is provided with automatic increase in duration of opening of injectors. In process of warming up duration of operating impulses on the oscillogram should be reduced continuously, gradually coming nearer to value typical for single turns.

In injection systems in which the injector of cold start is not applied, at cold start of the engine the additional operating impulses shown on the oscillogram in the form of pulsations of variable length are used.

In the table resulted more low typical dependence of duration of operating impulses of opening of injectors on a working condition of the engine is presented.

Inductive gauges

The increase in turns of the engine should be accompanied by increase in amplitude of a pulse signal developed by the gauge.

The electromagnetic valve of stabilisation of turns of idling (IAC)

In motor industry electromagnetic valves IAC of set of the various types which are giving out signals also of the various form are used.

The general distinctive feature of all valves is that fact that porosity of a signal should decrease with loading increase for the engine, connected with inclusion of additional consumers of the capacity causing fall of turns of idling.

If porosity of the oscillogram changes with loading increase, however at inclusion of consumers infringement of stability of turns of idling takes place, check up a condition of a chain of the electromagnetic valve, and also correctness given out ECM a command signal.

Usually in chains of stabilisation of turns of idling the 4-polar step-by-step electric motor which description is resulted more low is used. Check of 2-contact and 3-contact valves IAC is made in a similar manner, however oscillograms of alarm pressure given out by them are absolutely unlike.

The step-by-step electromotor, reacting on given out ECM a pulsing operating signal, makes step updating of turns of idling of the engine according to working temperature of a cooling liquid and current loading on the engine.

Levels of operating signals can be checked up by means of an oscillograph, measuring щуп which is connected serially to each of four plugs of the step-by-step motor.

Ljambda-probe (the oxygen gauge)

The increase in turns of the engine should be accompanied by increase of amplitude of a signal, reduction - decrease.

The detonation gauge (KS)

Ignition signal on an amplifier exit

At increase in turns of the engine frequency of a signal should increase in direct ratio.

Primary winding of the coil of ignition

Non-uniformity of throws can be caused excessive resistance of a secondary winding, and also malfunction of condition ВВ of a wire of the coil or a candle wire.