Chapter Three: Overview
Overview of Alarms
87
If a relay is set up as an actuated relay and an alarm condition arises, the relay will be configured
as shown in Figure 23.
Normally Open (Pin 11)
Normally Closed (Pin 13)
Relay B Common
(Pin 12)
Figure 23: Relay B during an Alarm Condition, when configured as an Actuated Relay
Refer to Table 21, page 65, for the pinouts of relays A and B, and Table 22, page 67, for the
pinouts of relays C and D.
The last user-defined function is the relay latching state. This parameter determines the alarm
relay behavior after an alarm condition ceases. If the relay latching state is activated (a low at the
rear panel input), a relay remains in its alarm position even after pressure drops below the alarm
trip point. If the relay latching state is deactivated (high), a relay returns to its previous position
after the pressure drops below the alarm trip point.
The alarm latching state can only be altered via a signal sent through the General I/O connector
on the rear panel (contact closure to ground), or with an RS-232 unlatch-all-alarmed-relays
command. If no latching signal is connected to the rear panel, the relay latching status is
deactivated (high), and the relay will switch contacts back and forth as the pressure crosses above
and below trip point.
For example, assume relay B is set to be actuated during an alarm condition, but the pressure is
still below the alarm trip point. The relay latching state for alarm B is not activated. When the
pressure rises above the trip point set for alarm B, relay B switches contacts (Figure 23). When
the pressure drops below the trip point again, the relay switches back to its previous position
because the relay latching state is deactivated.
Use relay B as our second example, and it is still set to be actuated during an alarm condition. In
this example, however, the latching state is activated. When the pressure rises above the trip
point set for alarm B, relay B switches contacts as it did before. The relay is said to be latched.
When the pressure drops below the trip point again, the relay does not change contacts. The
relay remains latched until it is unlatched via the General I/O connector, or through the RS-232
command (only possible if the pressure is below the trip point).
Default Settings of the Trip Point Alarms
Parameter
Default Setting
Actuation State
Actuated
Channel
1
Latching State
Disabled
Trip Point Value
1000 Torr
Table 36: Default Settings of the Trip Point Alarms
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