Emissions - Decreasing Fuel Consumption and Exhaust Gas Emissions in Transportation - page 84

A small size and a low price are the main preconditions for the wide ranging use
of sensors in transportation. There are different methods for the miniaturization of
sensors and actuators [ 20 ]:

• Combination of micro mechanical, micro electrical, and micro optical engi-
neering production methods;
• Utilization of uniform and flexible multibus interfaces, which is a standard
application in industrial computer systems;
• Combination of multi layer, hybrid, and semiconductor technologies;
• Application of small measurement errors with highly developed tuner

amplifiers;
• Changing analog signals to High Frequency signals for data transfer with low
hysteresis;
• Correction of sensor deviations at the measurement site;
• Comparison of measured values with stored basic values and compensation of
the sensor signals; and
• Storage of corrected information in the Electronic Programmable Read-Only
Memory (PROM)

Temperature, pressure, speed, number of revolutions, and inclination sensors
are widely used in all means of transportation. The direct analysis of combustion
products is still not state of the art and is one of the hardest measurement tasks.
One exception is the solid electrochemical technology for oxygen measurement.
These sensors are called Lambda tubes, operate with zirconium dioxide, and
optimally measure the O 2 concentration in the exhaust gas in two places—
upstream and downstream of the catalyst. The measuring tube consists of an
integrated heating element and provides the necessary operating temperature of
600C (1,112F) [ 21 ].
A changed form of Lambda sensor measures the NO concentration. Similarly
designed solid electrolytic measuring cells can be used for the analysis of
unburned substances such as CO and HC. Semiconductor and metallic oxide
sensors do not have the required accuracy and selectivity yet.
Anemometers, and Pitot and Prandtl tubes are important elements for the air
mass flow estimation in the air intake system for the combustion engine mea-
surement technology. The first operates with a heated wire, and the second with
combined pressure, sensors. The detector elements are usually installed in a
Wheatstone bridge to improve the precision of the signals [ 22 ].
The measurement of the mass flow of the exhaust gas is a very complicated
technology because of high temperatures and pressures, and fast changes of the
physical and chemical parameters in the combustion chamber and in the exhaust
gas after treatment system. The mass flow of individual combustion products in the
bend pipe of the combustion chamber and in the end pipe of the exhaust gas after
treatment system can be estimated only with highly complex technology to
achieve the required accuracy.