RKI Instruments RX-517 - Manual (Page 34)

PT0E-0730
33
１１．Detection principle
１１−１ ． NDIR method (Non-Dispersive Infrared)
The model is based on NDIR method (Non-Dispersive Infrared) and this structure is shown below.
The infrared beam emitted from the light source passes through the measuring cell, and optical
band pass filter which can pass the absorption wave of measuring gas and attains to the infrared
sensor. The amount of infrared attaining to the infrared sensor through the measuring cell and
will decrease according to its density.
The variable amount of infrared is measured by the infrared sensor and it is displayed as gas
concentration.
Then, there is no sensitivity against CO etc which have the different absorption wave from the
measuring gas. Then there is no sensitivity against N2 and H2 etc which cannot absorb infrared.
As compared with the conventional catalytic combustion method, there is no poisoning material
to be absorbed and almost no sensitivity drop on this detection principle.
１１−２． GALVANIC CELL method
Galvanic cell is consisting of a lead anode and a gold cathode in electrolyte covered by a
membrane. When oxygen enters into the gold cathode, a current which is directly proportional
to the oxygen concentration will be produced, and amplified current will produce a reading on
a meter in percent oxygen.
隔膜
陰極
電解液
サーミスタ
陽極
出力端子
構造図
Membrane
Lead electrode
(Anode)
Gold electrode
(Cathode)
Solution
Output terminal
Thermistor
Figure
Light source
Measuring cell
Detector
Out
Band path
filter
Amp