FB_HVAC2PointCtrl
Application
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 variable rW.
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 on-off controller.
bInvalidParameter: TRUE if an error occurs 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 on-off controller in relation to the upper/lower limits of the control deviation, with no switch-on or switch-off delay.
Figure 2:
Curve of switching output bOut for a on-off controller in relation to the upper limit rHighLimit = 3 and the lower limit rLowLimit = 8 with a switch-on delay of tDelayOn = 4 s and a switch-off delay of tDelayOff = 6 s.
