Basic Operation; Backup Level Override Parameters; Level Override Conditions - Siemens SITRANS LUT400 Operating Instructions Manual

General Operation
7.3 Discrete Inputs
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.
Note
A backup level override will prevent a fail-safe condition from occurring.
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.
7.3.1.1

Basic operation

Configuring Backup Level Override involves three steps (see Backup Level Override (2.9.1)
(Page 208) ).
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 Discrete Input Logic (2.9.2) (Page 208) ).
7.3.1.2

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.
Parameter
Level Override Value (2.9.1.2) (Page 208)
Discrete Input Number (2.9.1.3) (Page 208)
Enable (2.9.1.1) (Page 208)
When the level rises to 4.3 m and the switch is activated, the reading is forced to 4.3 m
where it stays until the switch is de-activated.
7.3.1.3

Level Override conditions

When the discrete input activates, the level output will immediately take on the value chosen
in step 1 above. The LUT400 LCD will indicate that the discrete input has been activated.
When a Backup Level Override condition clears (the discrete input is deactivated), the level
will return to the value determined from the ultrasonic transducer or, if no echo is available,
the device will enter the fail-safe condition.
92
Sample Value
4.3
DISCRETE INPUT 2
ENABLED
Operating Instructions, 07/2019, A5E33329501-AC
SITRANS LUT400