188 EL3000 CONTINUOUS GAS ANALYZERS | OI/EL3000-EN REV. D
… 13 Maintenance
ZO23 – Function Test
Description
The function test is used to carry out a rapid and regular check
of the response time of the sample cell.
The function test can be carried out without any test gases by
feeding the sample gas with constant concentration.
The function test has a very high correlation to a check with test
gases. In case of doubt, the latter is decisive, however.
The function test facilitates the preventive maintenance of the
gas analyzer, since a requisite exchange of the sample cell
becomes plannable through the change in the response time.
Procedure
In the function test, the build-up of an oxygen potential in the
sample cell is simulated through the connection of an electrical
test current.
The change in the oxygen potential correlates with the response
time of the sample cell. A small change in the oxygen potential
points to a relatively fast response time of the measuring cell.
In this case, the result of the function test is ‘Test Passed’.
If the value deviates from the value before the completion of the
test by more than 10 % of the value before the beginning of the
test, the result is rejected, since it is assumed that the change in
the sample gas was too high during the test.
Test factor
The test result can be tailored to the required response time. For
this purpose, the test factor can be set by the user within the
range 1 to 200 %. A test factor of 100 % is set ex works.
95
-time for gas change in 0 to 10 ppm measuring
%
s
%
s
If the test criteria are not met, the test factor must either be
changed or the sample cell checked by means of test gases.
Check of the sample cell using test gases
To check the T
95
-time, two test gases with differing
concentrations are required in the measuring range (see Sample
gas on page 28), for example a test gas with 2 ppm O
2
and a test
gas with 8 ppm O
2
.
The T
95
-time is determined through alternating application of
the test gases.
Beforehand, purge the test gas valves and the gas lines with
oxygen-free gas (e.g. with nitrogen from a loop feeder) or with
sample gas (flow rate 5 to 10 l/h, duration approx. 2 h).
Performing the function test
The function test takes approx. 15 minutes. It is therefore
recommended that it is carried out at a time when the process
control is not adversely affected thereby.
The function test is executed in 2 phases:
1. After start-up, the test current is applied to the sample
cell for approx. 400 s.
2. The test current is then switched off, and the function
test is ended after another 400 s.
Menu path
‘ Maintenance / Diagnosis / Test Functions /
Analyzer Test / ZO23 Function Test’
Show Test Result Passed: End test.
Failure: change test factor.
Impossible: Keep measured gas concentration stable
or use test gas.
Execute Test Start function test by selecting OK; the remaining
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