Honeywell VRX180 user manual Ratio Setpoint, Setpoint Select, SETPOINT#2, Soft PID YES, no

Programming Function Blocks and Features

Table 4-10 Loop Prompts (continued)

Prompt	Range/Selections	Definition
RATIO SETPOINT		Enter a number will equal the ratio that the ratio control loop
		will maintain between its process variable and a “wild
		variable.” The wild variable may be the Output Value of any
		analog input or calculated value function block over which the
		ration loop will have no control.
		The RATIO SETPOINT menu choice is essentially a multiplier
		applied to the wild variable’s value. This multiplication’s result
		will be a working set point for the loop that will ensure the
		desired “process variable-to-wild variable” ratio. For example,
		suppose you intend to use the ratio control loop to maintain a
		50% fuel-air ratio in the operation of a furnace. If the loop will
		be directly controlling air flow (i.e. - air flow will be the loop’s
		process variable) and fuel flow will be used as a wild variable
		to generate the ratio loop’s working set point, the RATIO
		SETPOINT menu choice will have to be set to 0.50. Hence, if
		fuel flow is measured to be 60, the working set point that will
		be used in the ratio loop’s control of air flow will be (60) x
		(0.50) = 30.
		To make a ratio control loop’s working set point equal to the
		product of RATIO SETPOINT and a specific wild variable
		value, the loop’s working set point must be toggled to SP2
		using the “SP (Set Point Select)” key while viewing the loop’s
		ON LINE display. Refer to Figure 4-1.
SETPOINT SELECT	OFF, discrete parameter, 0,	When the DISCR VS KEY SEL discrete is ON (1) this
	1	parameter takes the place of the On-Line Tune Loop menu’s
		Toggle Set point Source prompt.
		SETPOINT SELECT = ON (1) = Set point2
		SETPOINT SELECT = OFF (0) = Set point1
		When DISCR VS KEY SEL is OFF(0), SETPOINT SELECT
		has no effect.
SETPOINT#1 &	Set point #1 can be a	Set point #1 and #2 are independent set points. Either may be
SETPOINT#2	number only. Set point #2	the active set point for the loop. When viewing a live ON
	can be a number, an analog	LINE mode control loop display, a loop may be switched
	parameter, or OFF.	between SETPOINT #1 and SETPOINT #2 by accessing the
		Tune Loop menu and selecting TOGGLE SETPOINT
		SOURCE. Operation of the loop using SETPOINT #1 will be
		indicated by the presence of an “SP1” symbol on the loop’s
		display. “SP2” will be the symbol observed when the loop is
		operating using SETPOINT #2.
		While SETPOINT #2 may be programmed as a numerical
		value, it may also be used as a remote set point input to the
		loop. You may link SETPOINT #2 to any of several analog
		parameters that include the Output Values of analog input or
		calculated value function blocks. If used as a remote set point
		input, SETPOINT #2’s value may not be manually changed
		from within any live ON LINE mode control loop displays.
SOFT PID	YES, NO	Soft PID action (YES) causes the control algorithm to not
		calculate proportional output corresponding to errors resulting
		from changes to set point. The algorithm will adjust its Reset
		(Integral) term to a value required to maintain the present
		output when the set point is changed. Normal proportional
		action should occur for all changes and variations to the
		controlled variable.

98 Video Recorder – User Manual