Level relay
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Description
The FB_LevelRelay function block monitors a level and evaluates whether it is within a predefined range. It realistically maps normally closed and normally open contacts (13–14 / 21–22), including optional input enable and simulation mode. The internal state #Level_OK
signals a valid level; the outputs follow this state, taking the inputs into account.
Note: This logic is intended as a template. It must be integrated, tested, and approved by qualified personnel before productive use. Improper integration may result in incorrect level evaluation or unexpected switching behavior.
How it works
Reset
With #Reset
, the block is reset to a safe initial state: Normally closed contact ( #NO_13_14
) inactive, normally open contact ( #NC_21_22
) active (error/idle state). Status shows Reset, errors are reset.
Disabled
If #Enable
is not set, both contacts remain off. The block behaves passively without error indication.
Level rating
The current level ( #Level
) is checked: It is considered valid if it is between the lower and upper limits ( #LO_Limit ≤ #Level ≤ #HI_Limit
), then #Level_OK
is set.
simulation
In simulation mode, the contacts are controlled directly via #Level_OK
: Normally closed contact is activated when the level is valid, normally open contact when the level is invalid.
Normal operation
In real operation, the inputs also act as releases:
-
#NO_13_14
is only active if#Input_13
is set and the level is valid. -
#NC_21_22
is only active if#Input_21
is set and the level is out of range.
Status and diagnostics are reset if no errors are present.
Technical details
-
Inputs:
#Enable
,#Reset
,#SimMode
,#Level
,#LO_Limit
,#HI_Limit
,#Input_13
,#Input_21
-
Internal state:
#Level_OK
– TRUE if level is within the allowed range -
Outputs:
#NO_13_14
(normally closed),#NC_21_22
(normally closed) -
Status & Diagnosis:
#Error
,#Status
,#DiagnosticCode
- Modes: Reset, Disabled, Simulation, Real-time
- Logic: Area check with optional input release and realistic contact mapping
Possible applications
- Level control with defined switching conditions
- Pre-validation of level conditions in simulation mode
- Integration into process and alarm chains for status feedback
- Linking sensor values with approved contacts for safe processes
Note: A complete technical inspection and approval by qualified personnel is required before productive use.
compatibility
- Can be used in PLC systems with SCL support (e.g. Siemens TIA Portal)
- Modular integration into higher-level control, safety and diagnostic architectures
- Simulation allows safe tests without real level changes
- Safe basic state when deactivated
Scope of delivery
You will receive:
- An SCL file with the implemented function block FB_LevelRelay
- Complete declaration of all inputs/outputs and internal states
- Commented logic for quick adaptation
- Quick guide to integration into automation projects
The download link will be provided after purchase.
Support
I am happy to support you with:
- Adjustment of level limits and release logic
- Integration into control and alarm chains
- Simulation and validation before live use
- Specific extensions for your application
Contact is possible via shop message or email. Extensions are available as optional customizations.