7
GA0383P02 Rev. C
System Description
The GCM-A is primarily designed for use on air-cooled generators, although application to
other air-cooled machines is possible. Its main purpose is to provide early warning and
detection of overheating (or arcing) in these machines.
The major components of the GCM-A are the System Electronics and the sampling system.
System Electronics
The System Electronics consist of one display board, one controller board, one input/output
board, two airflow metering boards, one power supply, one vacuum pump, one cloud
chamber, one blower fan and one sampling manifold.
The System Electronics provide calibration, mode selection, alarm contacts, data logging,
system inputs/outputs and diagnostics.
Fail-safe operation of the GCM-A is assured by:
• On power-up the GCM-A must execute and pass qualifying self tests. Failure in any test
results in the suspension of operation and the annunciation of the condition causing the
failure.
• Following power-up and/or system reset, the GCM-A is continuously supervised by an
independent watchdog monitor that serves to reset it should its operation become
erratic.
• The GCM-A is completely self-supervised and continuously checks itself for legal
processor functioning, proper vacuum levels, internal voltages, communication accuracy,
integrity of cabling and relay operation. Any faults are immediately annunciated.
Display Panel
The Control/Display Panel provides control of all functions of the GCM-A as well as
complete annunciation of GCM-A’s status (Figure 17). Functions are accessed by means of
a four-button membrane-switch keypad and 20-character Liquid Crystal Display (LCD).
Generally, pressing the Fn (Function) key causes the LCD to continuously scroll the names
of the available functions. A function may then be accessed by pressing the Enter key when
the function name appears. See “GCM-A Menu Displays” for more information.
The Display Panel provides Light Emitting Diodes (LED’s) to annunciate GCM-A status; they
indicate Warning, Alarm and Trouble conditions. A green LED indicates AC Power.
Since all configuration constants are stored in non-volatile memory, these values will not be
lost should the system be initialized, or should it lose, then regain, AC power.
Input/Output Board
The Input/Output board assembly has terminal strips where all customer connections to the
relay and signal outputs are made. Wire access is provided by the three knockouts at the
top and/or bottom of the Enclosure.
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