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3.2.7. Cycle valve control panel
The Cycle Valve Control Panel provides both status and control, much like the Sample
Valve Control Panel. Status indicators include:
• Sample Pressure: This scale is psia or absolute pressure, measured at the gas cell.
The pressure is lowest during the Evacuation cycle. It peaks during the Analyze and
Background cycles (~ atmospheric or 14.7 psia). The scale confirms the proper
operation of the pumps and cycle valves.
• Cycle Status: LEDs light to show the stages of the scan cycle from Evacuation to
Analysis. The scan cycle is explained in the “Air sampling system.” A green LED
indicates the status is OK. An amber LED indicates a possible problem, i.e.,
inadequate pressure during the cycle.
• ZPD: The Zero Path Difference indicates the intensity of the infrared signal measured
by the detector.
• If the values are no longer in the green range, there may be a problem requiring service
attention.
• Control Panel Status: Refer to Control panel status. The Power On, Manual Mode, and
Comm. Active LEDs have the same functions on all three control panels.
The LEDs 1 to 8 light to indicate which valves are active during each sampling cycle. LEDs
1 to 6 correspond to valves S1-S6, with S7 and S8 provided for future use.
When the ACM 150 monitor is in Front panel Mode, press the buttons to activate the
momentary test switches for testing purposes. In other modes, the switches are inactive.
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