OZONE ANALYZER BMT 964 Manual, Rev. 04/2021
8
Photometers and Dirt
Using 254 nm UV radiation the ozone photometer "looks" through the gas, or the water, in
which the ozone is contained. It looks via two cuvette windows made of fused quartz. When
these windows become dirty the instrument cannot distinguish between a reduction of the UV
radiation by the ozone present in the cuvette - and the reduction by dirty cuvette windows. The
most important rule for operating an ozone photometer is: "The only real enemy of an ozone
photometer is dirt!"
When measuring ozone, namely in an industrial environment, it really pays off to thoroughly pro-
tect the ozone analyser from any dirt which might be contained in the ozone sample gas.
BMT ozone analysers for gaseous ozone are equipped with particle filters containing a replacea-
ble filter insert. The filter inserts should from time to time be checked for dirt (see page 29,
Maintenance), and be replaced on a regular basis depending on the degree of particle content of
the sample gas.
The ozone gas coming from most types of ozone generators contains more or less nitrogen ox-
ides because the oxygen feed gas contains nitrogen, inadvertently, or intentionally. Namely medi-
um sized and big generators are operated with high nitrogen doping. When such generators are
serviced without disconnecting the ozone analyser the danger of dirt getting into the analyser is
particularly high.
Caution: High concentration of nitrogen oxides in the sample gas must be avoided. If this could
occur e.g. during generator service, sample gas flow must be stopped!
The following two drawings show two possible configurations:
"bleed" flow
0.1 - 1l/ min
system flow
system pressure > a mbient pressure
measurement ta kes pla ce
at ambient pressure
"bleed" flow ra te depends
on system pressure
VENT mode
throttle
rota meter
vent to
ambient
ozone destruct
(low flow resistance)
OZON E
AN ALYZER
system flow any system pressure
bypass flow
0.1 - 1 l/ min
measurement ta kes pla ce
at system pressure
bypa ss flow rate depends
on system flow ra te
defined
flow resistance
PRESS mode
OZON E
AN ALYZER
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