OZONE MONITOR BMT 932 Manual, Rev. 02/2021
39
20 Trouble Shooting
19.1 Negative Ozone Concentration Values
Negative ozone concentration values do not exist, of course. But an ozone monitor actually can
display negative values. The reason is not fully understood. The mechanism probably is as fol-
lows: The scrubber is converting substances contained in the sample to something which pro-
duces an extinction of the UV radiation in the range of 254 nm used to measure the ozone. Dur-
ing the zeroing cycle the zero ozone reference is taken with this contaminated sample. During the
measuring cycle the contamination above is no more present (because the scrubber is no more
included in the sample gas line) and the sample is more transparent than before which means: the
concentration measured seems to be lower than it really is, even negative.
A wrong positive ozone concentration can be displayed by an ozone monitor when 1) the sample
contains substances which produce an extinction in the UV range around 254 nm, and 2) the
scrubber retains these substances partly or completely. Even without any ozone contained in the
sample, the extinction at about 254 nm is lower during the zeroing cycle than during the measur-
ing cycle which leads to a positive ozone concentration displayed which actually does not exist.
The problems mentioned above demonstrate the high importance of using a scrubber material
which is well adapted to the specific circumstances of the atmosphere in which the ozone content
shall be measured.
In case the BMT 932 has to be sent in for service, please use the following addresses:
BMT MESSTECHNIK GmbH
Hamburger Strasse 19
D-14532 Stahnsdorf, Germany
Tel. +49 - 3329 - 696 77 - 0, Fax +49 - 3329 - 696 77 - 29
http://www.bmt-berlin.de
service@bmt-berlin.de
North America
OSTI Inc.
P.O. Box 3320
Monterey, CA 93940, U.S.A.
Tel. +1 - 831 - 649 1141, Fax +1 - 831 - 649 1151
http://www.osti-inc.com
Please contact BMT MESSTECHNIK or OSTI Inc. before you send in any instruments.
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