Switcher Block (v3.0)

• Full function block name: Lib.Mervis.v3_0.SwitcherBlock
• Inherits from: Lib.Mervis.v2_0.BaseAlarmBlock
• Required project references: Lib.Mervis

PROGRAM PUMP_CONTROL_DEMO
    VAR
        Heating_Demand : BOOL;
        Pressure_Switch : BOOL;
        Thermal_Fault : BOOL;
 
        PumpSwitcher : Lib.Mervis.v3_0.SwitcherBlock;
        Pump_Relay : BOOL;
    END_VAR
 
    PumpSwitcher(
        Demand := Heating_Demand, 
        Feedback := BOOL_TO_USINT(Pressure_Switch), 
        Failure := Thermal_Fault,
        RunDown := T#2m,                // 2 minutes overrun to cool down
        FeedbackTimeout := T#10s        // Wait 10s for pressure to build up
    );
 
    Pump_Relay := PumpSwitcher.Command;
END_PROGRAM

Description of Feedback values

Description of ControlFlags values

Description of CompositeState output values

This block integrates standard, highly-used functionalities required for safely and effectively switching physical devices (such as pumps, fans, or compressors). The core capabilities include:

• Operating Modes: Supports Auto, Manual OFF, and Manual ON logic.
• Feedback Monitoring: Verifies that the physical device has actually started.
• Alarm Management:
  • Not Run (Fail to Start): Triggered if the block issues a Command, but the physical Feedback does not become active within the FeedbackTimeout period.
  • Failure: Triggered by an external fault signal mapped to the Failure input, or optionally by an EmergencyShutdown.
• Periodic Kick (Exercise Function): Prevents mechanical seizing (e.g., pump rotors during summer) by automatically running the device for a short duration at set intervals.
• Run-Down (Overrun): Keeps the device running for a specified time after the demand has ceased (crucial for dissipating residual heat).
• Emergency Shutdown: Instantly halts the device, overriding all internal logic.
• Maintenance Counters: Tracks total operating hours and start counts.

Execution Logic: A switch command is generated based on the Demand input (in Auto mode) or forced by the Manual ON mode. Once the Command is active, the block monitors the Feedback. If the feedback is not detected within the FeedbackTimeout, a Not Run alarm is generated.

If an external fault occurs (e.g., a frequency inverter fault or thermal overload), the Failure input generates a Failure alarm. Setting the EmergencyShutdown input to TRUE immediately deactivates the Command regardless of the selected operating mode.

In Automatic mode, the device may also start independently of the Demand if the KickFunctionInterval expires. It will run strictly for the KickFunctionDuration.

When the Demand becomes inactive, the run-down timer begins. The Command remains active for the duration specified by RunDown, ensuring safe shutdown procedures (like cooling down a boiler loop) are completed before the relay is finally deactivated.

This block is highly recommended for controlling physical outputs like circulation pumps or exhaust fans.

Scenario: Heating Circulation Pump In a standard commercial boiler room, a circulation pump must run whenever the heating controller requests heat (Demand). However, abruptly stopping the pump when the burner turns off can cause water to boil in the heat exchanger due to residual heat.

• By configuring the RunDown property to `T#2m`, the pump will continue circulating water for 2 minutes after the demand stops.
• During the summer, the pump is turned off for months. To prevent the impeller from seizing due to rust or sediment, the KickFunctionInterval is set to `T#7d` (7 days) and the KickFunctionDuration to `T#30s`.
• A differential pressure switch is wired to the Feedback pin. If the PLC turns the pump on but detects no water pressure within 10 seconds (FeedbackTimeout), it triggers an alarm to alert the facility manager of a broken belt or seized motor.