Functional Description; Explanation Of Terms; Exhaust Gas Sampling Probe; Measuring Chamber - Bosch BEA 070 Original Instructions Manual

3.8

Functional description

The BEA 070 records the absorption coefficients k [m
of the exhaust gas in compression ignition (diesel) en-
gines. To achieve this, some of the exhaust gas from the
tailpipe of the vehicle is conveyed via an exhaust gas
sampling probe and sampling hose to the measuring
chamber (without assisted suction ) while the vehicle is
accelerated freely.
The opacity, which is calculated from the absorption
coefficient, is measured.
3.8.1

Explanation of terms

The effective optical path length is the path of light
through which the exhaust gas flows. It measures
215 mm.
The opacity [%] and the absorption coefficient [m
are a measure of the quantity of light that is absorbed
by soot, white smoke and blue smoke.
The mass concentration [mg/m
of particulates in mg that are emitted by the diesel ve-
hicle for every 1 m of exhaust gas.
3
i
The basis for conversion of the absorption coef-
ficient into mass concentration is the conversion
table established by the British Motor Industry
Research Association (MIRA) .
3.8.2

Exhaust gas sampling probe

The exhaust gas sampling probes are designed such
that exhaust gas can be sampled in all types of exhaust
pipe. An adjusting mechanism ensures a minimum
insertion depth of 5 cm in the exhaust pipe.
Furthermore, the design guarantees a minimum dis-
tance of 10 mm from the inside wall of the exhaust
pipe.
3.8.3

Measuring chamber

For measuring opacity, a transmitter (LED) emits a
green light, which is partially absorbed by the exhaust
gas in the measuring chamber.
The proportion of light that is not absorbed reaches the
receiver (photo diode), and converts the optical signals
into electrical information.
Air curtains (a flow of purge air) prevent soot from
depositing itself on the optical windows.
The measuring chamber is equipped with a heater to
prevent water condensing on the walls of the chamber
and to keep the temperature of the exhaust gas above
dew point.
Zero position compensation takes place automatically.
Robert Bosch GmbH
]
-1
]
-1
] indicates the quantity
3
3.8.4

Correct operation

To ensure correct operation, the temperature of the
exhaust gas and the measuring chamber is continually
monitored.
In addition, zero position compensation takes place
before each measuring cycle. This incorporates a check
of the degree of contamination of the optical measuring
path.
If one of the above parameters is outside the permitted
tolerance, measurement is not possible.
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1 689 989 113 2018-06-08