mru OPTIMA 7 BIOGAS, Руководство пользователя

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MRU Instruments, Inc. USER MANUAL OPTIMA 7 BIOGAS
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5.2 Electrochemical measured principle
The oxygen content of the sample gas is measured with a 2 electrode electrochemical sensor.
Toxic gases like carbon monoxide (CO), nitrogen oxide (NO), nitrogen dioxide (NO
2
), sulphur dioxide (SO
2
), and hydrogen
sulphide (H
2
S) are measured with 3 electrode sensors.
The electrochemical sensors are based on gas diffusion technology.
The advantage of this technology is that the signal generated is direct proportionally and linear to the volume concentra-
tion (% or ppm) of the analysis gas components.
When the gas being measured contacts the sensing electrode, it reacts on the electrode surface either through oxidation
(for example CO, SO
2
, NO) or reduction (like NO
2
, and Cl
2
).
Example: CO sensor:
CO reacts at the sensing electrode as follows:
CO + H
2
O -> CO
2
+ 2H+ + 2e-
and at the counter electrode, oxygen from air will be re-oxidized to water:
½ O
2
+ 2H+ + 2e- -> H
2
O
The sensor supplies a constant current signal (
m
A-range) that is monitored and analyzed. The current intensity is depend-
ant upon the volume concentration of the sample gas, while other parameters like temperature and cross sensitivity are
calculated by the analyzer.
5.3 Principle of the IR-bench
A regulated infrared source (IR) provides light in the range of 2 to 8 microns (µm). The infrared light is directed through
the sample cell to the optical detector. The source is electronically modulated with no chopper wheels and no moving
parts.
The residual infrared energy, not absorbed by the sample gas, is guided to the optical detector. It passes an optical nar-
row band pass.
Infrared light passed through the filter is collected by a pyro-electric detectors. It produce a voltage that is proportional
to light intensity.
Unlike electrochemical sensors, the NDIR measurement shows no ageing due the gas concentration measured.
It’s lifetime is only limited by the lifetime of the IR source.
Pos.
1 Sample gas
2 Particle filter
3 Sensing Electrode
4 Reference Electrode
5 Counter Electrode
6 Connection pin
7 Electrolyte reservoir
8 Electrolyte
9 Capillary diffusion
barrier