Documentation

Min / Max Controller (T33)

Minimum and maximum controller

Block name

T33_MIN_MAX_CONTROLLER

ST call

PROGRAM TEST_T33
	VAR 
		REAL1,REAL2,REAL3,REAL4,REAL5,REAL6,REAL7,REAL8: REAL;
		BOOL1,BOOL2,BOOL3,BOOL4,BOOL5,BOOL6,BOOL7,BOOL8: BOOL;
		FB: LIB.HVAC.V1_0.T33_MIN_MAX_CONTROLLER;
	END_VAR
	FB(IN:= REAL1, WALARMAX:= REAL1, WALARMIN:= REAL2, WMAX:= REAL3, WMIN:= REAL4, XPALARMAX:= REAL5, XPALARMIN:= REAL6, XPMAX:= REAL7, XPMIN:= REAL8, BALARMAX=> BOOL1, BALARMAXN=> BOOL2, BALARMIN=> BOOL3, BALARMINN=> BOOL4, BMAX=> BOOL5, BMAXN=>BOOL6, BMIN=> BOOL7, BMINN=>BOOL8);	
END_PROGRAM

Library

LIB\HVAC

Version

V1.0

Description

The block monitors the measured value and announces exceeding of alarm limits.

Inputs

Outputs

Function

The block contains two pairs of comparators. When controlling water pressure in a heating system, the min signal is used to control the supply water valve, max signal to control the water drainage valve, min min signal to disable all aggregates, and max max signal to indicate the maximum system pressure level. Other values can be monitored and controlled as well, like temperature, humidity, etc. Hysteresis prevents hunting at the setpoint value.

The hysteresis, or Xp band, is used to prevent flickering of the output signal.

Similar applies for the alarm signals:

The block can be used to control pressure, water level, but also 2-point heating and cooling systems. It is useful thank to four comparators in one block which save schema space and improve legibility.

Application example

The block compares the measured water pressure PWATER with the pressure setpoint PWATERSETPT. As soon as the pressure drops below the min value, the water valve SOLENOIDVALVE opens, when the pressure rises above WMIN + HYSTERESE the valve closes. When the WALARMAX or WALARMIN are teached, the alarms are invoked. The min min pressure disables the boiler and pump operation. The operation is restored only after the alarm has been acknowledged and reset (the MEMORY output must be FALSE).