FB_HVAC2PointCtrl

This function block represents a 2-point controller. The controller is enabled via bEnable = TRUE and is then active.

VAR_INPUT

eDataSecurityType    : E_HVACDataSecurityType;
bSetDefault          : BOOL;
bEnable              : BOOL;
rW                   : REAL;
rX                   : REAL;
bReset               : BOOL;

eDataSecurityType: If eDataSecurityType:= eHVACDataSecurityType_Persistent, the persistent VAR_IN_OUT variables of the function block are stored in the flash of the computer if a value changes. For this to work, the function block FB_HVACPersistentDataHandling must be instanced once in the main program, which is called cyclically. Otherwise the instanced FB is not released internally.

A change of value can be initiated by the building management system, a local operating device or via a write access from TwinCAT. When the computer is restarted the saved data are automatically read back from the flash into the RAM.

Application example: example_persistent.zip

If eDataSecurityType:= eHVACDataSecurityType_Idle the persistently declared variables are not saved in a fail-safe manner.

Notice
A cyclically changing variable must never be linked with the IN_OUT variable of a function block, if eDataSecurityType:= eHVACDataSecurityType_Persistent. It would lead to early wear of the flash memory.

bSetDefault: If the variable is TRUE, the default values of the VAR_IN_OUT variables are adopted.

bEnable: The controller is enabled via a TRUE and is then active.

rW: The setpoint is transferred with the rW variable.

rX: The actual value of the control loop is transferred with the rX variable.

bReset: Acknowledge input in the event of a fault.

VAR_OUTPUT

bOut              : BOOL;  
bInvalidParameter : BOOL;

bOut: Switching output of the two-point controller.

bInvalidParameter: TRUE if an error has occurred during the plausibility check. The message must be acknowledged with bReset.

VAR_IN_OUT

rHighLimit      : REAL;
rLowLimit       : REAL;
bDirection      : BOOL;
tDelayOn        : TIME;
tDelayOff       : TIME;

rHighLimit: Upper limit of the control deviation (0..32767). The variable is saved persistently. Preset to 0.

rLowLimit: Lower limit of the control deviation (0..32767). The variable is saved persistently. Preset to 0.

bDirection: The control direction of the controller is determined by bDirection. FALSE = heating mode; TRUE = cooling mode. The variable is saved persistently. Preset to 0.

tDelayOn: Switch-on delay [s]. The variable is saved persistently. Preset to 0 s.

tDelayOff: Switch-off delay [s]. The variable is saved persistently. Preset to 0 s.

Timing characteristics

Figure 1:

Curve of switching output bOut for a two-point controller in relation to the upper/lower limits of the control deviation, with no switch-on or release delay.

Figure 2:

Curve of switching output bOut for a two-point controller in relation to the upper limit rHighLimit = 3 and the lower limit rLowLimit = 8 with a switch-on delay of tDelayOn = 4s and a release delay of tDelayOff = 6s.

Requirements

Development environment	required library	required function
TwinCAT 3.1 build 4022.16 or higher	Tc2_HVAC V3.3.1.0	TF8000 \| TC3 HVAC V1.0.0.0