RKI Instruments GD-70D Series - Manual (Page 75)

Detection principle
- 75 - GD-70
Detection principle
<Electrochemical Type>
The electric potential between the working
electrode and reference electrode is kept at a
certain level by a potentiostat circuit.
The gas to be detected is electrolyzed directly at
the working electrode. Because the electric
current generated there is proportional to the gas
concentration, the gas concentration can be
known by measuring the electric current flown
between the working electrode and the opposite
electrode.
Special precautions for this principle
1.
The detector is interfered by gases other than the gas to be detected, solvents, vapors, etc.
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 (threshold limit value) 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.
Because the contact point of the gas detector sensor is made of porous polymeric membrane, the water
repellency of the membrane is deteriorated by solvents, thus causing an electrolyte leak from its inside.
Do not use solvents near the detector. If you must use a solvent for unavoidable reasons, attach the
recommended filter to the inlet of the gas detector while using the solvent and for one hour after that.
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.
Electrolyte
R (Resistance)
Reference
electrode
Opposite
electrode
Working
electrode
Gas
permeable
membrane
Gas in
Gas out
Structure diagram
Potentiostat circuit