Setting Measurement Gas Temperature And Pressure - YOKOGAWA ZR22G User Manual

8.7.5

Setting Measurement Gas Temperature and Pressure

The analyzer calculates the moisture content contained in exhaust gases and saturated water
vapors from the entered gas temperature and pressure to obtain the relative humidity and dew
point. The relative humidity may be obtained using the following theoretical equation (JIS Z
8806).
To obtain the relative humidity:
The relative humidity U that is obtained from JIS Z 8806 is:
U = e/es x 100
where, e = water vapor pressure of moist air
Since the gas-pressure ratio is equal to the volume ratio, the above equation may be expressed
mathematically by:
U = P x H/ es x 100
where, P = Gas pressure
The saturated water vapor pressure es is determined by a gas temperature, so the relative
humidity can be obtained by entering the above parameters.
To obtain the dew point:
The dew point is the temperature at which a water vapor pressure in the moist air is equal to the
saturated water vapor pressure.
The water vapor pressure in the moist air can be obtained from the gas pressure ad volume ratio
(= pressure ratio), as given below.
e = P x H
where, e = water vapor pressure in moist air
Use the above equation to find the water vapor in the moist air, and use the theoretical equation
(JIS Z 8806) to obtain the temperature at which that water vapor is equal to the saturated water
vapor pressure.
Setting Measurement Gas Temperature, Pressure
l
There are two ways of entering measurement gas temperatures: one is to measure actual gas
temperature using a temperature transmitter and the other is to enter a preset value manually.
Set the measurement gas temperature as follows:
(1) "Sensor menu" > "Setting"
(2) Select "Input temp./press. setting".
(3) "Select Humidity model setting".
(4) When you select "Temperature ipunt selection", a dialog box appears to select "Preset
value", "External input". Select according to your system.
When "preset value" is selected
(5) Enter the measurement gas temperature on "input temperature setting".
When "external input" is selected
(6) Enter the values of temperature of 4 mA point and 20mA point respectively of a temperature
transmitter you use.
(7) Select "Temp. upper limit alarm value" or "Temp. lower limit alarm value" when using an
alarm caused by temperature of measured gases. Enter the alarm temperature from the
numeric entry screen
es = Saturated water vapor
H = moisture content (volume ratio)
P = gas pressure
H = Humidity (moisture content) (volume ratio)
<8. Detailed Data Setting>
IM 11M12G01-02EN
8-26
1sh Edition : Mar. 25, 2021-00