RKI Instruments GD-70D Series - Manual (Page 80)

Detection principle
GD-70D - 80 -
<Galvanic Cell Type>
By immersing precious metal and lead in electrolyte and
connecting them with a lead wire, a battery can be made
(galvanic cell). When oxygen passes through the barrier,
deoxidizing reaction occurs at the precious metal electrode
while oxidizing reaction occurs at the lead electrode.
The electric current generated by this reaction goes
through load resistance (thermister), where it is converted
into voltage so that it can be read. When the oxygen
concentration is decreased, deoxidizing reaction at the
precious metal electrode is also decreased, thus lowering
the voltage at both ends of the thermister.
Special precautions for this principle
1.
The readings of the detector fluctuate slightly in response to changes in the air pressure. In particular, be
careful of alarm activation when a low air pressure is brought in by typhoon. The environmental
(temperature, humidity, etc.) changes in the installation site may also have influences on the readings.
2.
The alarm must be set within a range where the performance of the detector can be ensured. The
standard alarm setpoint is 18 vol%.
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.
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 sensitivity calibration are
performed for every six months.
Barrier
Negative
electrode
Electrolyte
Thermister
Positive
electrode
Output terminal
Structure diagram