Free Acceleration Method; Description Of Function - Bosch RTM 430 Instandsetzungsanweisung

2.5 Free acceleration method

2.6 Description of function

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The diesel engine is accelerated without external load (it is operated only against the mass
of the engine). A measuring cycle covers idling, acceleration to maximum engine speed
following by idling again.
In order to measure the opacity, an emitter (LED) emits green light which is partially
absorbed by the exhaust gas in the cylindrical measurement chamber (length = 430 mm).
The non-absorbed light share reaches the receiver (photodiode) which converts the
optical signals to the electrical information which can be further-processed by
downstream evaluation units.
Soot deposits on the optical windows are avoided by air curtains, i.e. scavenging air
flowing tangentially past them.
The measurement chamber features a heater in order to avoid water condensation on the
measurement chamber wall and in order to keep the exhaust-gas temperature above the
dew point.
A measurement cannot conducted if the exhaust-gas temperature lies below the dew
point.
Zero adjustment is performed automatically by switching the valve over to fresh air.
Functions to guarantee proper operation include constantly monitoring the exhaust-gas
temperature and the measurement-chamber temperature which can be read out in the
service program.
In addition, a zero adjustment is performed prior to each measuring cycle, also including
a check of the degree of contamination of the optical measuring path.
If one of the aforesaid parameters is out of tolerance, measurement is no longer possible
and an error message is displayed in clear text.