Honeywell VRX180 user manual Function Block Types, Why use function blocks?, Function block

Programming and Operating Concepts

Table 3-3 Function Block Types

Function block	Type		Maximum	Purpose
name			available*
Alarm	AL	96		Causes alarms under specified conditions.
Analog Input	AI	48		Interfaces with measuring input hardware (thermocouple,
				RTD, mA, volts).
Analog Output	AO	8		Interfaces with analog output hardware (current output
				(CAT)) or with output relay hardware (time proportion
				(DAT)).
Calculated Value	CV	96		Performs various calculations on specified parameters.
Constant	CN	32		Outputs a number or an analog parameter value.
Discrete Input	DI	36		Interfaces with discrete input hardware (dry contact
				closure).
Discrete Output	DO	36		Interfaces with output relay hardware (AC relay, DC
				relay, mechanical relay, open collector output).
Loop	LP	8		PID or ON/OFF control with various outputs.
Setpoint Profiler	SP	4		Generates a time-varying setpoint for a loop’s Setpoint
				#2.
System	SY	1		Outputs discrete status of alarms, data storage, and
				diagnostics; outputs analog value of reference junction
				temperature. This function block is not programmable; its
				outputs are produced automatically.
Totalizer	TL	48		Outputs accumulated total over time.

* Depends on options ordered.

Why use function blocks?

Function blocks give you configuration flexibility. For instance, the instrument does not have a dedicated relay that is activated during an alarm; instead, you can program any of several Alarm function blocks to control any relay. Also, there is not a specific input for your process variable; any of several Analog Input function blocks can be programmed to be your process variable. In general, function blocks let you connect the output parameter of any function block to the input parameter of any function block.

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