Description Of Function - Bosch BEA 750 Original Instructions Manual

en 24 | BEA 750 | Product description
4.8

Description of function

The BEA 750 is used to measure the exhaust gas
components CO, HC, CO
2
be retrofitted). The excess air factor (Lambda) is
calculated on the basis of the gas values measured.
The non-dispersive infrared method (NDIR – non-
dispersive infrared spectroscopy) is employed for
measuring the CO, CO and HC quantities. The oxygen
2
is determined using a sensor with electro-chemical
action.
Warm-up time
The BEA 750 warm-up time is approx. 1 minute.
Measurements cannot be taken during this period.
Zero calibration at the start of exhaust emissions
tests
After switching on the pump, the zero point of the
analysis system is automatically calibrated (duration
30 seconds) with ambient air (zero gas).
Zero calibration during exhaust emissions tests
Following the start of an exhaust emissions test, the
BEA 750 automatically implements a system check
with ambient air at irregular intervals. To perform the
system check, the BEA 750 switches a solenoid valve
to ambient air. The system is flushed with zero gas
for 30 seconds. An active carbon filter removes the
hydrocarbons from the ambient air drawn in.
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, O and NO (NO can
2
Lambda air ratio measurement
The BEA 750 calculates the excess air factor (Lambda)
from the measured HC, CO, CO
concentrations.
Precise oxygen measurement is important for
Lambda calculation. Lambda calculation and oxygen
measurement must be activated for this purpose.
The Lambda value is calculated with the aid of the
Brettschneider formula:


[ ]
CO
[ ] [ ]

H
+ + +
CV
CO O x
2 2

4
2


λ
=
 
H O
CV CV
+ −
 
1 x
 
4 2
[] Concentration in % by vol, also for HC
K Conversion factor for HC from NDIR to FID (value 8)
1
Hcv Hydrogen/carbon ratio in the fuel (typically 1.7261) *
Ocv Oxygen/carbon ratio in the fuel (typically 0.0175) *
* Dependent on the fuel used.
Oxygen measurement
The BEA 750 is equipped with an O
sensor is a wearing part.
The oxygen measurement is automatically adjusted to
the air oxygen content of 20.9 % by vol and is required
for Lambda calculation.
and oxygen
2


[ ]
O (
3 5 , [ ] [
CV 
− +
x CO CO
[ ] 2

CO
2
+ 
3 5 ,

CO
2
( )
[ ] [ ] [ ]
+ +
CO CO K x HC
2 1
sensor. The O
2 2
Robert Bosch GmbH
)
]