SCR air humidity and air temperature combination sensor, component description

B14.40-0003-06

Represented in vehicle 382.154

Arrangement

3 Combined sensor of air humidity and air temperature SCR (17B01)

The combined sensor of air humidity and air temperature SCR (3) is located on the outside part of the intake tube, between the air filter and the turbocharger.

Task

The combined air humidity and temperature sensor (3) measures the temperature and determines the water steam content in the intake air.

B14.40-0082-05

Represented in vehicle 634.011

3 Combined sensor of air humidity and air temperature SCR (17B01)

Composition

The combined air humidity and temperature sensor (3) consists of separate components to determine the temperature and to measure air humidity.

The components to determine the air humidity are "active", i.e., are supplied with tension. Unlike the components for measuring the temperature which are "passive".

Humidity sensor

To transmit the humidity, inside the sensor is a plate type capacitor with two plates and a layer of humidity sensitive synthetic material as insulator. The insulator is applied to the bottom plate. In the top plate there is an electrode permeable to water steam.

Temperature sensor

An NTC "Negative Temperature Coefficient" resistor is located inside the sensor to measure the temperature and means, that the electrical resistance diminishes when the temperature increases.

Function

Transmission of the humidity

The synthetic material layer, between the two capacitor plates, is sensitive to humidity and can store water molecules. The capacity and electrical conductivity changes, according to the humidity value of the air taken in.

This change in resistance also depends highly on the temperature and has to be compensated by the air temperature measurement. The values that modify in the electrical capacitor are transmitted at defined intervals as analog signals, to the MR control module. The MR control module calculates the relative air humidity, considering the determined value of the air temperature

Measuring of air temperature

The air that flows, depending on the temperature, influences the temperature measurement of the element inside the sensor and, therefore, the amount of electrical resistance.

The values that change themselves in the electrical resistance are transmitted at defined intervals as analog signals, to the MR control module. Based on the resistance value, the MR control module calculates the corresponding temperature