下降警报
下降报警由以下参数的下降水平引起：
测量值超过预先配置的阈值，还将导致：相关报警LED点亮。n、 锁存报警器
锁定报警是一种即使在监测的液位不再超过报警阈值。警报LED将保持点亮，直到操作报警复位。
o、 非锁存报警非锁定报警是指仅在被监控的液位超过报警阈值。报警指示灯报警级别保持时，将保持点亮，但将自动点亮当监测的液位不再超过报警阈值时复位。
p、 正常通电断电时，正常通电继电器激活例如，在系统电源故障的情况下）。LED将发生报警或故障时点亮，无论继电器处于配置状态。
q、 正常断电通电时，正常断电继电器激活（例如，在报警条件下）。LED将点亮
发生报警或故障时，无论继电器如何配置状态。
r、 延时报警（仅限2Vx软件版本）
响应某些继电器的报警事件的操作可能是：通过对继电器应用延迟功能进行修改。时滞函数
可在以下情况下将继电器的激活延迟一段时间：发生报警事件和/或在一段时间内保持继电器激活
报警事件清除后。延时设施可用仅用于高完整性中继卡的中继RL2至RL8。
延时功能有助于防止虚假报警，并确保外部电气设备的适当最小运行时间
连接到继电器的装置。控制卡版本
自System 57最初推出以来，有几个新功能：已添加以增强5701控制卡的功能。
每个软件版本的关键功能如中所示下表。请注意，安装在现有卡上的软件不能：
升级，但所有版本的软件和硬件都已完全升级
向后兼容，因此新卡可以合并到现有卡中毫无困难的系统
Falling Alarm
A falling alarm is caused by a falling level of the parameter being
measured crossing a preconfigured threshold and will also cause
the associated alarm LED to illuminate.
n. Latched Alarm
A latched alarm is an alarm that will remain active even though the
level monitored no longer crosses the alarm threshold. The alarm
LED will remain lit until the alarm reset is operated.
o. Non-latched Alarm
A non-latched alarm is an alarm that only remains active while the
level being monitored crosses the alarm threshold. The alarm LED
will remain lit while the alarm level remains but will automatically be
reset when the level monitored no longer crosses the alarm threshold.
p. Normally Energised
A normally energised relay is activated when the power is removed
from it, (eg. in the event of a system power failure). The LEDs will
illuminate when an alarm or fault condition occurs irrespective of the
relay configured state.
q. Normally De-energised
A normally de-energised relay is activated when the power is applied
to it, (eg. in the event of an alarm condition). The LEDs will illuminate
when an alarm or fault condition occurs irrespective of the relay
configured state.
r. Time Delay Alarms (Version 2Vx Software only)
The operation in response to alarm events of certain relays may be
modified by applying a delay function to the relays. Time delay functions
are available to delay the activation of a relay for a short period after
an alarm event occurs and/or to maintain relay activation for a period
after the alarm event has cleared. The time delay facilities are available
for relays RL2 to RL8 of the High Integrity Relay Card only.
The time delay function is useful to prevent spurious alarms and to
ensure appropriate minimum operating times for external electrical
apparatus connected to the relay.Control Card Versions
Since the original launch of System 57 several new features have
been added to enhance the capabilities of the 5701 Control Card.
The key features for each software version are illustrated in the
following table. Note that the software fitted to existing cards cannot
be upgraded, however all versions of software and hardware are fully
backward compatible so new cards can be incorporated into existing
systems without difficulty
