Siemens SITRANS LUT400, Operating Instructions Manual

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A5E33329501 SITRANS LUT400 (HART) – OPERATING INSTRUCTIONS Page 69
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Relays controlled by HART Communications
A relay can be controlled directly by a remote system through communications. HART
commands can be used for this purpose. An expert knowledge of HART, and the use of
HART commands is recommended. For further details on configuring relays controlled by
HART, contact your Siemens representative.
Discrete Inputs
SITRANS LUT400 has two discrete inputs to trigger or alter the way SITRANS LUT400 controls
devices. A Backup Level Override, Pump Interlock, or a Switch (DI) Alarm can be configured
using discrete inputs, and discrete input logic can be reversed if necessary for the application.
Backup Level Override
Backup level override provides the option of overriding the ultrasonic input (signal from a
transducer) with another contacting point level device, such as the Pointek CLS200, to
determine the level output.
The material reading is fixed at the programmed switch level until the discrete input is
released. The LUT400 makes its decisions based on the override value.
Backup Level Override functionality is particularly useful in wet-wells and reservoirs that
use pumps:
• place a backup level switch high in a vessel to indicate when it is about to overflow
• place a backup level switch low in a vessel, to indicate when it is almost empty.
Basic operation
Configuring Backup Level Override involves three steps (see
2.9.1. Backup Level Override
).
1. Select a level override value. This will be the Level output produced by the
instrument when the backup level override condition is present.
2. Select the discrete input that is connected to the point-level device.
3. Enable the Backup Level Override function.
It may also be necessary to invert the logic of the discrete input, which is possible through the
LUT400 discrete input logic parameters (see
2.9.2. Discrete Input Logic
).
Backup Level Override parameters
Example:
SITRANS LUT400 is configured for a level measurement. In the same application,
Discrete Input 2 is connected to a Hi Level Backup switch at a level value of 4.3 m.
Note: A backup level override will prevent a fail-safe condition from occurring.