Table of Contents
Advertisement
Troubleshooting & Service
7.3.5. INABILITY TO ZERO - NO ZERO BUTTON
7.3.6. NON-LINEAR RESPONSE
234
•
Check for leaks in the pneumatic systems as described in Section 7.5. Leaks can
dilute the span gas and, hence, the concentration that the analyzer measures may
fall short of the expected concentration defined in the CONC sub-menu.
•
If the low-level, hardware calibration has drifted (changed PMT response) or was
accidentally altered by the user, a low-level calibration may be necessary to get the
analyzer back into its proper range of expected values. One possible indicator of
this scenario is a slope or offset value that is outside of its allowed range (0.7-1.3 for
slope, -20 mV to 150 mV for offsets). See Section 7.6.4 on how to carry out a low-
level hardware calibration.
In general, the T200H/M will not display certain touchscreen buttons whenever the
actual value of a parameter is outside of the expected range for that parameter. If the
calibration menu does not show a ZERO button when carrying out a zero calibration, the
actual gas concentration must be significantly different from the actual zero point (as per
last calibration), which can have several reasons.
•
Confirm that there is a good source of zero air.
•
Check to make sure that there is no ambient air leaking into zero air line. Check for
leaks in the pneumatic systems as described in Section 7.5.
The T200H/M was factory calibrated to a high level of NO and should be linear to
within 1% of full scale. Common causes for non-linearity are:
•
Leaks in the pneumatic system. Leaks can add a constant of ambient air, zero air
or span gas to the current sample gas stream, which may be changing in concentra-
tions as the linearity test is performed. Check for leaks as described in Section 7.5.
•
The calibration device is in error. Check flow rates and concentrations, particularly
when using low concentrations. If a mass flow calibrator is used and the flow is less
than 10% of the full scale flow on either flow controller, you may need to purchase
lower concentration standards.
•
The standard gases may be mislabeled as to type or concentration.
concentrations may be outside the certified tolerance.
•
The sample delivery system may be contaminated. Check for dirt in the sample
lines or reaction cell.
•
Calibration gas source may be contaminated (NO
•
Dilution air contains sample or span gas.
•
Ozone concentration too low because of wet air in the generator. Generator system
needs to be cleaned and dried with dry supply air. Check the permeation dryer for
leaks. This mostly affects linearity at the low end.
•
Sample inlet may be contaminated with NO
Verify proper venting of the pump exhaust.
•
Span gas overflow is not properly vented and creates a back-pressure on the
sample inlet port. Also, if the span gas is not vented at all and does not supply
enough sample gas, the analyzer may be evacuating the sample line. Make sure to
create and properly vent excess span gas.
•
Diffusion of oxygen into Teflon-type tubing over long distances. PTFE or related
materials can act as permeation devices. In fact, the permeable membrane of NO
Teledyne API - Model T200H/T200M Operation Manual
in NO gas is common).
2
exhaust from this or other analyzers.
X
Labeled
2
07270D DCN7141
Advertisement
Table of Contents
