KANOMAX 6501 series Climomaster - Manual (Page 55)

54 Principle of Measurement
Measurement of Wind-Temperature
(MODEL 6531/6541/6542/6533/6543/6561)
The coefficient of resistance of the temperature sensor has a
direct proportional relationship with the temperature. We can
measure the wind temperature by adjusting the sensor’s
temperature to the wind-temperature, and measuring its
coefficient of resistance.
Measurement of Humidity (Hygrometer)
(MODEL6531/6533)
The sensor is a pair of condensers and its
electro-capacity is dependent upon the amount of
water contained in its hydrophilic macromolecule
(humidity sensitive) membrane.
The components of the sensors are a glass
foundation; a lower electrode; a macromolecule
membrane and an upper electrode.
The upper electrode will capture the change in
permittivity caused by condensation or
evaporation of water vapors to the macromolecule
membrane. (Electrostatic Capacity Type)
There is another type of hygrometer that uses a resistor instead of a condenser.
Typically Electrostatic Capacity types are good for low humidity measurements and the
resistor types are good for high humidity measurements.
Theory of detecting static pressure (MODEL6501-B0/6501-C0)
To measure static pressure, we use a diffusion-type semiconductor pressure sensor.
The diffusion-type semiconductor pressure sensor is incorporated under the principle
that the resonant frequency of a piezo-crystal decreases linearly with the pressure
applied. On a thin diaphragm of silicon, there are four diffusion resistors (sensor chips)
placed in a fixed distant apart. (Pic.1)
When the pressure is applied from above, the diaphragm will deflect downward. When
it is deflected, the sensors near the center (R3 and R4) will have compressing stress and
the sensors near the perimeter (R1 and R2) will have tensile stress instead. (Pic.2) The
diffusion coefficient of the diffusion resistor changes according to these two stresses.
If we create a bridge among these diffusion resistors (Pic.3), it is possible to detect
voltage that is proportional to the amount of pressure applied. These sensors can be
affected by the temperature, and therefore, a temperature compensation circuit must be
added.
Pic.2
Upper
Electrode
Lower
Electrode
Glass
Foundation
Macromolecule
Membrane
Diaphragm
Pressure
Pic.1 Pressure Sensor
R1 R
R4
R1～R4：Diffusion Resistant
R3
Pic.3 Detecting Circuit
R1
R2 R4
R3
Cur
ren
t
i
Output
Wind
Temp Sensor
(Platinum Resistor)
Wind