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Teledyne API - Model T200H/T200M Operation Manual Troubleshooting & Repair
233
next step. Do not leave the Perma Pure dryer without filter for more than a few
seconds, as you may draw in dust, which will reduce the performance of the dryer.
A leak between the flow meter and the reaction cell (where the flow-determining
critical orifice is located) may cause a low flow (the system draws in ambient air
through a leak after the flow meter). Check for leaks as described in Section 7.5.
Rep
air the leaking fitting, line or valve and re-check.
The most likely cause for zero or low ozone flow is a clogged critical flow orifice or
sintered filter within the orifice assembly. The orifice that sets the ozone flow is
located on the reaction cell. Check the actual ozone flow by disconnecting the tube
from the reaction cell and measuring the flow going into the cell. If this flow is
correct (see Table 10-3 for flow rates), the orifice works properly. If this flow is low,
replace or clean the orifice. The orifice holder assembly allows a quick and easy
replacement of the orifice, refer to Section 6.3.6 on how to do this. Appendix B lists
a spa
re part kit with a complete orifice assembly that allows a quick replacement
with minimum instrument down-time. The clogged orifice can then be cleaned while
the instrument is running with the replacement.
7.2.4. HIGH FLOW
Flows that are significantly higher than the allowed operating range (typically ±10-11%
of the nominal flow) should not occur in the T200H/M unless a pressurized sample, zero
or span gas is supplied to the inlet ports. Ensure to vent excess pressure and flow just
before the analyzer inlet ports.
When supplying sample, zero or span gas at ambient pressure, a high flow would
indicate that one or more of the critical flow orifices are physically broken (very
unlikely case), allowing more than nominal flow, or were replaced with an orifice of
wrong specifications. If the flows are within 15% higher than normal, we recommend to
re-calibrate the flow electronically using the procedure in Section 4.13.7.5, followed by
a regular review of these fl
ows over time to see if the new setting is retained properly.
7.2.5. SAMPLE FLOW IS ZERO OR LOW BUT ANALYZER REPORTS
CORRECT FLOW
that the T200H/M analyzer can report a correct flow rate even if there is no or a low
actual sample flow through the reaction cell. The sample flow on the T200H/M is only
calculated from the sample pressure and critical flow condition is verified from the
difference between sample pressure and vacuum pressure. If the critical flow orifice is
partially or completely clogged, both the sample and vacuum pressures are still within
their nominal ranges (the pump keeps pumping, the sample port is open to the
atmosphere), but there is no flow possible through the reaction cell.
Although measuring the actual flow is the best method, in most cases, this fault can also
be diagnosed by evaluating the two pressure values. Since there is no longer any flow,
the sample pressure should be equal to ambient pressure, which is about 1 in-Hg-A
higher than the sample pressure under normal operation. The reaction cell pressure, on
the other hand, is significantly lower than under normal operation, because the pump no
longer has to remove the sample gas and evacuates the reaction cell much better. Those
two indicators, taken together with a zero or low actual flow, indicate a clogged sample
orifice.
The T200H/M features a orifice holder, which makes switching sample and ozone flow
orifices very easy, refer to Section 6.3.6 on how to change the sample orifices and
Appendix B for part num
bers of these assemblies. Again, monitoring the pressures and
07270B DCN6512