A-3-8 Appendix 3: ZO23 Trace Oxygen Analyzer Module 42/24-10 EN Rev. 9
Function Test
Description The function test is used to carry out a rapid and regular check of the response
time of the measuring cell. The function test can be carried out without any
additional test gases by feeding the sample gas with constant concentration. It
has a very high correlation with the check using gas. 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 measuring cell becomes plannable
through the change in the response time. The values determined in the function
test are stored in the log. As a result, the progression of the response time of the
measuring cell can always be traced back.
Procedure In the function test, the build-up of an oxygen potential in the measuring cell is
simulated through the connection of an electrical test current. The change in the
oxygen potential correlates with the response time of the measuring 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 beginning of the test by more than 10 %
after completion of the function 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. In this connection,
the test factor can be set by the user within the range 1 to 200 %. A test factor of
100 % is set ex works.
Test factor 1 to 99 % Test requirements lower T90 time > 60 s
Test factor 100 to 200 % Test requirements higher T90 time ≤ 60 to 20 s
If the test criteria are not met, the test factor must either be changed or the meas-
uring cell checked by means of test gases.
Check of the
Measuring Cell Using
Test Gases
Two test gases with different concentrations within the measuring range are
required to check the T95 time, e.g. a test gas with 2 ppm O
2
and one with 8 ppm
O
2
(refer to “Information for the Installation and Sample Conditioning”, page A-3-4).
The T95 time is determined through alternate application of the test gases. Before-
hand, purge the test gas valves and the gas supply line 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 hrs).
Carrying out 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:
Test current on
After start-up, the test current is applied to the measuring
cell for approx. 400 s.
Test current off
The test current is then switched off, and the function test
is ended after a further 400 s.
Menu Path MENU → Maintenance/Test → Analyzer spec. adjustm. →
ZO23 function test
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