Protecting From Water Droplets; Cross Sensitivity With Other Gases - Michell Instruments XZR200 User Manual

XZR200 User's Manual
5.2.2

Protecting from Water Droplets

In environments where falling water droplets are likely, the sensor should be protected
from water falling directly onto the very hot sensor cap as this can cause massive
temperature shocks to the cell and heater. Popular methods include a hood over the
sensor cap or for the sensor to be mounted in a larger diameter cylinder.
At a very minimum the sensor cap should be angled downwards in the application as
this will defl ect any falling moisture and prevent the sensor cap from fi lling with water
(see Section 3, Installation).
5.2.3

Cross Sensitivity With Other Gases

Gases or chemicals that will have an infl uence on the life of the sensor or on the
measuring results are:
1. Combustible Gases
Small amounts of combustible gases will be burned at the hot Platinum
electrode surfaces or Al2O3 fi lters of the sensor. In general, combustion
will be stoichiometric as long as enough oxygen is available. The sensor
will measure the residual oxygen pressure which leads to a measurement
error (low oxygen reading). The sensor is not recommended for use in
applications where there are large amounts of combustible gases present
and an accurate O
Gases tested:
• H2 (Hydrogen) up to 2%; stoichiometric combustion
• CO (Carbon Monoxide) up to 2%; stoichiometric combustion
• CH4 (Methane) up to 2.5%; stoichiometric combustion
• NH3 (Ammonia) up to 1500 ppm; stoichiometric combustion
2. Heavy Metals
Vapors of metals like Zn (Zinc), Cd (Cadmium), Pb (Lead) and Bi (Bismuth)
will have an effect on the catalytic properties of the Pt– electrodes. Exposure
to these metal vapors must be avoided.
3. Halogen and Sulphur Compounds
Small amounts (< 100ppm) of Halogens and/or Sulphur compounds have no
effect on the performance of the oxygen sensor. Higher amounts of these
gases will, in time, cause readout problems or, especially in condensing
atmospheres, corrosion of sensor parts. These gases often outgas from
plastic housings and tubes when hot.
Investigated gases were:
• Halogens, F
• HCL (Hydrogen Chloride), HF (Hydrogen Fluoride)
• SO
• H
• Freons
• CS
Michell Instruments
measurement is required.
2
(Flourine), Cl
2
(Sulphur Dioxide)
2
S (Hydrogen Sulphide)
2
(Carbon Disulfi de)
2
GOOD MEASUREMENT PRACTICE
(Chlorine)
2
15