Mercedes S-Class
+ Mercedes-Benz cars of the class S (W-140)
+ Operation manual
+ Routine maintenance
+ Engine
+ Cooling systems, heating
+ Power supply system and release
- Engine electric equipment
- Systems of ignition and engine management - the general information
Checks of a control system of ignition and injection
Search of malfunctions - the general information and preliminary checks
Check and adjustment of a corner of an advancing of ignition
Spark plugs
Self-diagnostics of systems of electronic control of OBD
Diagnostics of electronic system of the automatic air conditioner (AC)
Application of an oscillograph for observation of signals of a control system
Ignition coils - installation details
Removal, installation and adjustment of the sensor of position of the camshaft (CMP)
The distributor of ignition (M119.97 engines) - installation details
+ Systems of a charge and start
+ Gear shifting box
+ Automatic transmission
+ Coupling
+ Brake system
+ Suspension bracket and steering
+ Body
+ Onboard electric equipment
Application of an oscillograph for observation of signals of a control system
General information
Digital multimeters perfectly are suitable for check of the electric chains which are in a static state, and also for fixing of slow changes of the traced parameters. When conducting the dynamic checks which are carried out on the working engine and also at identification of the reasons of sporadic failures the oscillograph becomes absolutely irreplaceable tool.Some oscillographs allow to keep oscillograms in the built-in module of memory with the subsequent conclusion of results to the press or their transfer to the carrier of the personal computer already in stationary conditions.
The oscillograph allows to observe periodic signals and to measure tension, frequency, width (duration) of rectangular impulses, and also levels of slowly changing tension. The oscillograph can be used when performing the following procedures:
a) Identifications of failures of unstable character;
b) Checks of results of the made corrections;
c) Activity monitoring a lambda probe of a control system of the engine equipped with the catalytic converter;
d) The analysis of the signals developed a lambda probe which deviation of parameters from norm is unconditional the evidence of violation of serviceability of functioning of a control system in general. On the other hand, correctness of a form of the impulses given by the sensor can serve as a reliable guarantee of lack of violations 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 obtained information can be easily made by elementary visual comparison of the oscillograms removed during check with the temporary dependences typical for various sensors and actuation mechanisms of automobile control systems given below.
Parameters of periodic signals
General information
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Characteristics of any periodic signal |
Everyone, removed by means of an oscillograph signal, can be described by means of the following key parameters:
a) Amplitude: the maximum and minimum tension (V) of a signal within the period;
b) Period: Duration of a cycle of a signal (ms);
c) Frequency: Number of cycles per second (Hz);
d) Width: Duration of a rectangular impulse (ms, microsec);
e) Porosity: The repetition period relation to width (In foreign terminology the return is applied porosity the parameter called by a running cycle, expressed in %);
f) Signal form: Sequence of rectangular impulses, single emissions, sinusoid, sawtooth impulses, etc.
Usually characteristics of the faulty device strongly differ from reference that allows the skilled operator easily and to quickly reveal the refused component by the analysis of the corresponding oscillogram.
Signals of a direct current
The only performance data of such signals is tension.Signals of a direct current are developed by the following devices:
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Sensor of temperature of cooling liquid of the engine (ECT) |
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The sensor of temperature of the soaked-up air (IAT) |
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Sensor of provision of a butterfly valve (TPS) |
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Warmed up a lambda probe |
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Measuring instrument of a volume expense of a stream of air (VAF) |
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Measuring instrument of mass of air (MAF) |
Signals of alternating current
The main characteristics of these signals are amplitude, frequency and a form of a signal.|
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Sensor of a detonation (KS) |
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Inductive RPM meter of the engine |
Frequency-modulated signals (WC)
Performance data of frequency-modulated signals are amplitude, frequency, a form of a sig