Boiler Interlocks

medium

Combines pressure, level, and flame inputs into a burner permissive and reports which condition is blocking.

What it teaches

A safety permissive is a multi-input AND — every condition must be true for the burner to run. The industrial half: when the permissive is down, the operator needs to know why, so each condition also drives its own blocking-status flag. Teaches the interlock-plus-annunciator pattern every burner panel uses.

Parameters

Tag	Direction	Type	Default	Description
In_Run	Input	BOOL	0	Operator run request for the burner
In_Pressure	Input	REAL	5.5	Boiler steam pressure in bar
In_Level	Input	REAL	60	Drum water level in percent
In_FlameOK	Input	BOOL	0	Flame safeguard healthy; 0 means a flame fault
Cfg_HiPressure	Input	REAL	8	Pressure at or above this blocks the burner
Cfg_LoLevel	Input	REAL	30	Level below this blocks the burner
Out_Burner	Output	BOOL	0	Burner run command
Sts_Permissive	Output	BOOL	0	1 while every interlock is satisfied
Sts_PressureBlock	Output	BOOL	0	1 while high pressure is blocking the burner
Sts_LevelBlock	Output	BOOL	0	1 while low water level is blocking the burner
Sts_FlameBlock	Output	BOOL	0	1 while the flame safeguard is blocking the burner

Required behavior

Sts_PressureBlock is 1 while In_Pressure is at or above Cfg_HiPressure.
Sts_LevelBlock is 1 while In_Level is below Cfg_LoLevel. A level exactly at Cfg_LoLevel does not block.
Sts_FlameBlock is 1 while In_FlameOK is 0.
Sts_Permissive is 1 only while all three blocking flags are 0.
Out_Burner is 1 while In_Run and Sts_Permissive are both 1.
The blocking flags report whether or not In_Run is 1, so the operator can see what is holding the burner before asking for it.
More than one flag can be 1 at the same time. Each flag reports its own condition only.
Nothing latches. When a condition returns inside its limit its flag clears at once, and Out_Burner resumes on the same run request.
A change to Cfg_HiPressure or Cfg_LoLevel takes effect immediately.