AirShortage

AirShortage (FB)

FUNCTION_BLOCK AirShortage

Short description

Detection of an air shortage situation and generation of a fault message Typical application: air shortage monitoring on a fan with a differential pressure switch

Representation

Interfaces

Inputs

Name	Data type	Value range	Initial value	Function
xPFb	BOOL			Input process feedback (differential pressure switch), FALSE = air shortage
xFanFb	BOOL			Fan running indication
xQuit	BOOL		FALSE	Reset of the fault message

Outputs

Name	Data type	Value range	Initial value	Function
xAlarm	BOOL			Output - fault message
tTimeToAlarm	TIME			Time duration until the fault message is triggered

Setpoints / parameters

Name	Data type	Value range	Initial value	Function
udiControlTime	UDINT	1s … 3600s	30s	Waiting time until input xPFb is evaluated
xControl	BOOL		TRUE	Enable monitoring

Function description

General

This function block is used to detect an air shortage situation at a fan by evaluating the signals input - differential pressure switch xPFb and operating feedback - fan xFanFb.

Output - fault message xAlarm

The output - fault message xAlarm is activated (xAlarm = TRUE), if the conditions 1 and 2 below are met simultaneously. Condition 1: The input for the differential pressure switch xPFb is in the state FALSE for at least the waiting time udiControlTime permanently (= air shortage situation). At the same time monitoring is generally enabled (xControl = TRUE). Condition 2: The operating feedback for the fan xFanFb is in the state FALSE for at least the waiting time udiControlTime is permanently in the state TRUE (= fan running). At the same time monitoring is generally enabled (xControl = TRUE). The output - fault message xAlarm is deactivated in the following cases (xAlarm = FALSE): Case 1: Conditions 1 and / or 2 are not met and the reset of the fault indication xQuit is active (= TRUE). Case 2: Conditions 1 and/or 2 are not met and the monitoring enable xControl is not active (= FALSE).

Time duration until the fault message is triggered tTimeToAlarm

At the output time duration until the fault message is triggered tTimeToAlarm different values are displayed depending on the operating situation. Situation 1: Output of the remaining time until the fault message is triggered (conditions: xPFb = FALSE, xControl = TRUE, xFanFb = TRUE) Situation 2: If situation 1 does not apply, the value 0.0 is output continuously.

CODESYS

InOut:

Scope	Name	Type	Initial
Input	xPFb	BOOL
Input	xFanFb	BOOL
Input	xQuit	BOOL	FALSE
Input Const	udiControlTime	UDINT	30
Input Const	xControl	BOOL	TRUE
Output	xAlarm	BOOL
Output	tTimeToAlarm	TIME