RKI Instruments GD-70D Series - Manual (Page 79)

Detection principle
- 79 - GD-70D
<Semiconductor Type>
Metal dioxide can measure gas concentration based on changes
in the electric conductivity of semiconductor caused by gas
accumulated on its surface.
RL: Load resistance Vo: Output voltage
VH:Heater voltage Vs: Sensor voltage
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 sensing part of the gas detection sensor installed in this detector is made of porous sintered
bodies. If silicon or sulfide compounds are accumulated on the surface of porous sintered bodies, the
area of the gas sensing part becomes smaller, which may results in serious deterioration of its sensitivity.
For safety reasons, do not use the detector under presence of silicon or sulfide compounds even though
their amount is very small.
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.
Vs
VH
RL Vo