Setting The Alarm Limits - Honeywell 7866 Operation And Maintenance Manual

Calibration
5.8

Setting the Alarm Limits

Each 7866 Digital Controller/Indicator can be supplied with two alarms and two alarm relay outputs as a
standard. (Second alarm is mutually exclusive with 4-20 mA ranging output.) The alarms are set to operate
in Range 3 only. The intention of the alarms is to detect the loss of Hydrogen for the sealed system. The
assumption is that the lost Hydrogen will be replaced with atmospheric air.
Alarms are indicated on the left side of the display. When an Alarm is "in force," a number "1" or "2" will
be visible.
Alarm 1
Ideally the sealed system is filled to 100 % Hydrogen. As the hydrogen percentage falls the first alarm will
engage. The default setting is 98.0 %. The alarm setpoint can be adjusted to suit the process requirement.
When the alarm trips the normally open relay will de-energize and the relay contact will close. This relay
contact can be used to interlock the system with the main process controller or wired to an alarm bell or
flasher.
See wiring diagram in Section 3.7 for more detail (Figure 3-5) on the alarm terminal configuration.
Alarm 1 may also be used to call for make up Hydrogen. The alarm will activate when the measured
percentage of hydrogen falls below the setpoint. A deadband, also called "hysteresis", will prevent clearing
of the alarm until the measured Hydrogen is below the setpoint by 0.5 percent.
Alarm 2
(mutually exclusive with 4-20 ranging output)
When installed, the second alarm is intended to identify significant losses of Hydrogen. Alarm 2 is set to
90.0 percent Hydrogen at the factory. This alarm should be set to warn operators and the main process
control system of impending danger. With the inclusion of Air in the hydrogen filled system, there is a
serious possibility of combustion. The relay contact that is linked with this alarm should be wired to an
alarm annunciating horn, flasher, and/or shutdown safety system.
Alarm 2 is connected to Relay Output #1. See wiring diagram in Section 3.7 for more detail (Figure 3-5) on the alarm
terminal configuration.
Alarm will activate when the measured percentage of hydrogen falls below the setpoint. A deadband, also
called "hysteresis", will prevent clearing of the alarm until the measured Hydrogen is above the setpoint by
0.5 percent.
56 7866 Triple Range Digital H and CO Analyzer/Indicator - Operation and Maintenance
2 2
9/06