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General Operation
7.3 Discrete Inputs
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 211) ).
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 212) ).
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 212)
Discrete Input Number (2.9.1.3) (Page 212)
Enable (2.9.1.1) (Page 212)
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, 04/2021, A5E33329501-AG
SITRANS LUT400
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Troubleshooting
