Model 4802A
16
There is a unique situation that may occur with some frequency in certain applications.
An alarm may occur and the operator will accept this alarm by pressing the
Master
Accept
Button. If the alarm output is latching and the condition at the sensor returns to
normal (safe) the alarm output will need to be reset, as previously stated in Section 4.4.
If, however, the alarm output is not reset and that alarm set point is exceeded again, the
front panel LED, the associated mimic open collector, and the unaccept outputs will re-
flash or re-activate. This gives the operator an indication of a new alarm condition that
must be re-accepted.
A type of alarm, other than the A1 & A2 alarms, is the fault alarm. The fault alarm can be
accepted similarly to the A1 & A2 alarms. The front panel
Fault
LED will flash and the
fault unaccept (FUA) open collector will energize when a fault is detected. By pressing
the
Accept
button on the front panel, the FUA output will de-energize and the
Fault
LED will stop flashing. It will stay illuminated until the fault condition is corrected.
4.5 Resetting Latched Alarms
The user may select a “latching” or “non-latching” alarm output for A1 and/or A2. If an
alarm output activates and the condition that caused that activation is no longer present,
a non-latching alarm output will reset automatically. A latched alarm output needs to be
reset manually.
Resetting latched alarm outputs is accomplished with the
Master Reset
Button located
on the Facilities Module (FM002A). Pressing the
Master Reset
Button will reset any
latched conditions that are no longer valid.
NOTE -
Latched alarm conditions cannot be Reset until they have been Accepted (see
Section 4.4).
EXAMPLE -
The sensor detects a gas concentration in excess of an alarm set point (trip
level). The associated alarm outputs will activate. After a few moments, the gas
concentration drops below the alarm set point. If the alarm outputs are latched and
Accepted, the operator can press the Master Reset Button and the latched alarm
outputs will return to their normal (safe) state.
4.5.1 LED Test
The
Master Reset
Button performs another function. If the operator presses and holds
the
Master Reset
Button for two or more seconds, all of the LED’s and LED segments
in the digital display will illuminate for as long as the operator presses the button. This is
called the LED Test. The LED test cannot be performed while the unit is in alarm or
fault, or during a Card Test.
4.6 CAL/INH Open Collector
There is an open collector that will energize anytime the unit is put in the:
•
calibration
•
calibration
check
•
setup
•
setup
check,
or
•
inhibit
mode.
This open collector output is referenced to the system’s ground/common. Energizing this
output merely provides a path to ground as is the case with all energized open collector
outputs. De-energized, this output will be in a high impedance state.
