FourToTwoPipes (FB)¶

FUNCTION_BLOCK FourToTwoPipes

Control support for four-to-two-pipe assembly.

Application example¶

A four-to-two-pipe assembly consists of two shut-off valves (for heat / cool pipe) plus a control valve. They are used in plants to connect two-pipe aggregates to four-pipe supply.

Functionality¶

FourToTwoPipes takes care to control the shut-off valves to ensure they are not open in parallel. There are optional service indications (from shut-off valves) and a close-time to achieve this. In the rare case shut-off valves provide service indications it’s advisabe to use them. Otherwise FourToTwoPipes needs to rely on a properly configured close-time definitely covering travel time of shut-off valves plus safety reserve.

By construction four-to-two-pipe assemblies are supposed work in operation modes heat / cool / closed. Setpoints of the heat / cool sequence (0..100%) are scaled to the setting range (r*Begin..r*End - default 0..100%). The valve operation mode eModeIn can eventually provided by a specifc temperatur controller algorithm - in this case eModeOut follows the eModeIn. In case eModeIn is UNUSED, eModeOut is computed comparing rHeatSetpt / rCoolSetpt > 0.

Some controller algorithms may apply control range constraints - eventually a lower limit > 0%. In this case the setpoints of the heat / cool sequences will become inconsistent to determine the valve operation mode from. If the controller algorithm doesnt provides a valve operation mode, but inconsistent heat / cool sequences FourToTwoPipes falls back to heat.

InOut:

Scope	Name	Type	Initial	Comment
Input	`xEnable`	`BOOL`	TRUE	Enable
	`rHeat`	`REAL`		Heat control signal (0..100%).
	`rHeatBegin`	`REAL`	0.0	Heat control range begin (0..100%).
	`rHeatEnd`	`REAL`	100.0	Heat control range end (0..100%).
	`rCool`	`REAL`		Cool control signal (0..100%).
	`rCoolBegin`	`REAL`	0.0	Cool control range begin (0..100%).
	`rCoolEnd`	`REAL`	100.0	Cool control range end (0..100%).
	`eModeIn`	HeatCoolOperationMode	HeatCoolOperationMode.UNUSED	Controller operation mode.
	`tClose`	`TIME`	TIME#1m0s0ms	Close time - minimum time both shut-off valves needs to be closed.
	`xSvciHeatClosed`	`BOOL`	FALSE	Service indication - heat shut-off valve is closed
	`xSvciHeatClosed_Used`	`BOOL`	FALSE	Service indication svciHeatClosed is used / connected.
	`xSvciCoolClosed`	`BOOL`	FALSE	Service indication - cool shut-off valve is closed
	`xSvciCoolClosed_Used`	`BOOL`	FALSE	Service indication svciCoolClosed is used / connected.
	`itfDateTimeProvider`	`Util.IDateTimeProvider`	Globals.g_dtpDateTimeProvider	Source for the current date and time information in milliseconds since 1.1.1970 00:00:00.000
Output	`xHeat`	`BOOL`		Heat shut-off valve - TRUE if open
	`xCool`	`BOOL`		Cool shut-off valve - TRUE if open
	`rControl`	`REAL`		Control valve signal (0..100%).
	`eModeOut`	HeatCoolOperationMode	HeatCoolOperationMode.INACTIVE	Operation mode.
	`xError`	`BOOL`		Error indication - rEnd = rBegin or rSetpt out of range 0..100%.
	`eErrorID`	Error		Error ID