RKI Instruments GD-70D Series - Manual (Page 76)

Detection principle
GD-70D - 76 -
<Pyrolysis-Particle Type>
When the gas to be detected is heated to several hundred
degrees, particulate solid oxides are formed.
This is a sensor to detect particles formed in such a way by using
the α ray absorbing method.
Structure
This unit consists of a pyrolyzer which heats gas to several
hundred degrees and a particle detector which detect oxides.
The pyrolyzer has a quartz pipe at its center covered with a
heating element and a heat insulator around it.
The particle detector consists of the measurement box in which α
ray always generates ion current and the compensation box
which has the identical structure (gas is not introduced).
Principle
When most of organic metal (MO) gas, such as TEOS,
are heated, particulate oxides are formed. Sample gas
which is decomposed to oxides in the Pyrolyzer is
introduced into the particle detector.
Inside of the measurement box of the particle detector,
the α ray radiation source *1 ionizes the air and
generates ion current.
Ion current is also generated in the compensation box,
and its ratio is maintained at a certain level in both the
measurement box and the compensation box when no
gas is present. When particles are introduced into the
measurement box, the particles adsorb ions, thus
reducing the ion current. Its ratio to the compensation
box changes, which can be obtained from the detector.
* 1: Am-241 37kBq
Special precautions for this principle
1.
The detector is interfered by gases other than the gas to be detected, and vapors.
Please note that the alarm can be triggered by interference. In addition, it may be fluctuated by
environmental (temperature, humidity, etc.) changes in the installation site.
2.
The alarm must be set within a range where the performance of the detector can be ensured.
In facilities compliant with the High Pressure Gas Safety Act, an alarm setting below our standard alarm
setpoint may trigger a false alarm.
3.
This is a safety device, not a control device.
The alarm contact output of the detector must be used for an external alarm lamp/buzzer, while the
alarm signal output must be used for an indicator or external recorder. If these outputs are used to
control other devices, we shall not be responsible for any malfunctions.
4.
The gas detection sensor unit attached to the detector contains a small amount of radioactive materials.
Do not disassemble it, or dispose of it like other wastes. (For information on how to handle the sensor,
see the "Safety Manual".)
5.
For maintenance of the detector, it must go through a regular maintenance, including replacement and
adjustment of the regular replacement parts as specified in the operating manual. In addition, because
this is a safety device, it is recommended that a regular maintenance and gas calibration are performed
for every six months in accordance with the regulations.
Heat insulator
Heater
Gas
Quartz pipe
(Pyrolyzer)
High input impedance amplifier
V +
V
-
Sample gas
Measurement box
Insulator
Output
Collector electrode
Compensation box
(Particle detector)
Am-241
Am-241
A