Miscellaneous; Relay Behaviour Under Fail-Safe Conditions - Siemens SITRANS LUT400 Operating Instructions Manual

Miscellaneous

Totalizer and samplers
Other Pump Controls
Refer to
closure is approximately 200 ms duration.

Relay behaviour under fail-safe conditions

A fail-safe condition generally indicates that the level reading is not reliable or is unknown. In
such a situation, pumps will not run and alarms (that are based on level or a derivative
reading) will not activate. The following describes this behaviour in detail, by relay function.
Alarm relays
Any alarm that is based on level, or a reading derived from level such as flow rate, will not
activate if there is a fail-safe condition. If the fail-safe condition occurs and the alarm is
already active, the alarm will de-activate.
The following alarm types will de-activate during a fail-safe condition:
• High Level
• Low Level
• In-bounds Level
• Out-of-bounds Level
• High Flow Rate
Low Flow Rate.
•
Note: A dedicated alarm exists for fail-safe condition as described above. See
safe fault
on page 65.
Pump relays
If a pump cycle is in progress at the time the fail-safe condition occurs, then the pump cycle
will end prematurely (as if the 'off' setpoints were reached). This has the effect of turning off all
pumps immediately. If a pump run-on occurrence was scheduled for the pump cycle,
occur
. However, if a pump run-on occurrence has already begun at the time the fail-safe
condition occurs, then the run-on will complete.
If no pump cycle is in progress at the time the fail-safe condition occurs, then subsequent
pump cycles will not occur (the fail-safe condition will prevent pumps from starting), until the
fail-safe condition is cleared.
Miscellaneous relays
External Totalizer relay
If the external totalizer is in the process of recording volume (i.e. the relay is clicking) when a
fail-safe condition occurs, then the current series of clicks will be allowed to complete.
When totalizing volume:
Since pumps do not run when in fail-safe, then the external totalizer will in general not
operate either. If a fail-safe condition occurs during a pump cycle then the volume
pumped for that cycle will
Page 66 SITRANS LUT400 (HART) – OPERATING INSTRUCTIONS
on page 87. Relays are normally de-energized, contact
not
be totalized.
Fail-
it will not
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