PN 305200901, Rev YT
Since the ow control is a closed loop method of control, troubleshooting and
isolating the Proportional Solenoid Valve (PSV) versus the Flow Meter can be
slightly dicult. First, focus on the control of the PSV. This proportional valve is
ever neither completely closed nor completely open. During normal operation,
its duty cycle range is approximately 45–50 % (or, 45–50 % open). To check the
PSV duty cycle, observe the Flow Duty parameter on the Monitor tab.
As the Reference and Sample Period timers count down during their corre-
sponding cycles, you can observe the ow duty number changing in order to
maintain the 50 SCCM ow rate, regardless of the path or leg the gas is owing
through. If you notice that during the Sample Countdown period, the ow
seems to be controlled, but during the Reference period the ow seems to
drift out of tolerance, then you have isolated the ow problem to the Refer-
ence path or leg. Try removing the Reference Dryer and installing a jumper
or bypass in its place (1/8-inch tubing). There could be some obstruction in
the Dryer (internal). As a result, even when the PSV valve is at its maximum
duty cycle, a higher pressure dierential will be needed to overcome the ow
obstruction. This will cause the electronic feedback loop ow control to fail.
If after removing the Dryer the ow problem persists and you cannot deter-
mine if it is in either the Sample or Reference legs, the next step will be to re-
place the Flow Meter. Contact AMETEK to purchase a Flow Meter replacement
kit (PN 305449901S). If the new Flow Meter still does not x the problem, the
last step will be to replace the PSV valve (PN 230510001).
In summary, ow problems could be caused by one or more of the following
factors:
• Inlet pressure, Outlet pressure, or both.
• Partially or fully plugged capillary or manifold.
• Bad PSV valve, Flow Meter, or both.
• Software problem. Software problems on ow are not common, but
should be considered and checked. AMETEK will have you check software
parameters if needed.
4-16 | 3050-OLV Moisture Analyzer
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