Teledyne 400E, Instruction Manual, Page: 221 / 318

Model 400E Ozone Analyzer
Instruction Manual THEORY OF OPERATION
P/N 04316 Rev: B 221
The Measurement / Reference Cycle consists of:
Time Index Status
0 seconds Measure/Reference Valve Opens to the Measure Path.
0 – 2 seconds
Wait Period. Ensures that the Absorption tube has been adequately flushed of
any previously present gasses.
2 – 3 seconds
Analyzer measures the average UV light intensity of O
3
bearing Sample Gas ( I )
during this period.
3 seconds Measure/Reference Valve Opens to the Reference P ath.
3 – 5 seconds
Wait Period. Ensures that the Absorption tube has been adequately flushed of O
3
b3earing gas.
5 – 6 seconds
Analyzer measures the average UV light intensity of Non-O
3
bearing Sample Gas
( I
0
) during this period.
CYCLE REPEAT EVERY 6 SECONDS
10.1.4.
Interferent Rejection
The detection of O
3
is subject to interference from a number of sources including,
SO
2
, NO
2
, NO, H
2
O, aromatic hydrocarbons such as meta-xylene and Mercury
vapor. The Model 400E’s basic method or operation successfully rejects interference
from most of these interferents.
The O
3
Scrubber located on the Reference Path (see Figure 10-2) is specifically
designed to ONLY remove O
3
from the Sample Gas. Thus the variation in intensities
of the UV light detected during the instrument’s Measurement Phase versus the
Reference Phase is ONLY due to the presence or absence of O
3
. Thus the effect of
interferents on the detected UV Light intensity is ignored by the instrument.
Even if the concentration of interfering gases were to fluctuate so wildly as to be
significantly different during consecutive Reference and Measurement Phases, this
would only cause the O
3
concentration reported by the instrument to become noisy.
The average of such noisy readings would still be a relatively accurate
representation of the O
3
concentration in the Sample Gas.
Interference from SO
2
, NO
2
, NO and H
2
O are very effectively rejected by the model
400E. The two types of interferents that may cause problems for the Model 400E
are aromatic hydrocarbons and mercury vapor.