59
12
Appendix
12-1. Detection principle of Non-Dispersive Infrared
Ray
The Model RI-600 applies the Non-Dispersive Infrared Ray Absorption (NDIR) technique to detect target
gas. The infrared beam emitted from the light source passes through the gas cell and reaches the IR
sensor. The target gas enters the gas cell from the gas inlet.
When the target gas enters the gas cell, the amount of infrared ray received by the IR sensor decreases
since the infrared ray emitted from IR source is absorbed by the target gas.
This decreased amount is detected by IR sensor and output as gas concentration. There is an optical band
pass filter in front of IR sensor which allows the absorption wave of the target gas to pass through.
Then, there is no sensitivity for the gas which has the different absorption wave from the target gas.
Furthermore, there is no sensitivity against N
2
and H
2
etc. which cannot absorb infrared ray.
12-2. Definition of terms
ppm
Gas concentration indicated in the unit of one-millionth of the volume
vol%
Gas concentration indicated in the unit of one-hundredth of the volume
Calibration
Find relationship of the readings, display values or setpoints with the actual values
by using the calibration gas, etc.
Maintenance
mode
When maintenance is performed on the monitor, the alarm contact is disconnected,
and a signal to indicate the maintenance mode status is sent out to the external
output signal. As a result, maintenance can be performed on a single unit of the
monitor.
Initial clear
The reading is unstable for a few seconds after the power is turned on. To prevent
malfunctions for that period, the alarm contact is deactivated. In addition, a signal
to indicate the initial clear status is sent out to the external output.
Zero
suppression
A function to cut off the influences of environmental changes, interference gases,
etc.
Alarm delay time
A function which temporarily suspends alarm activation to prevent a false alarm
caused by outside noise.
Infrared Ray
CO2
in Air
Infrared light
Gas cell
Infrared sensor
Dust filter
Optical filter
タ
Display
Analog output
Contact