Honeywell VRX180 Pretune Loop, Stages Of Pretune, Pretune Stopped menu, Pretune Stopped Prompts

Online Operation Using Menus

Pretune Loop

Pretune calculates optimum values for a loop's Proportional Band/Gain, Reset and Rate by analyzing the reaction of the loop to a "step change" in setpoint or output. After these new tuning values have been calculated you have the option of applying (installing) or not applying them to a preselected tune set of the loop. You can pretune a loop while another loop is pretuning.

To use pretune, your process time constant must be at least 60 seconds. The process time constant is defined as the time needed for the PV to change by 63% of a step change in the setpoint. For example, if the setpoint changes instantaneously by 100 degrees, the time constant is the amount of time needed for the PV to change 63 degrees.

To pretune a loop, select PRETUNE from the TUNE LOOP online menu. Select a loop to tune. Pretune occurs in 4 stages as indicated by the status. Each status has its own menu. Table 7-10 shows the stages of pretune.

		Table 7-10 Stages Of Pretune
Order	Status	Meaning
1	STOPPED	Pretuning not operating, waiting to be started by operator. See STOPPED menu.
2	IDENTIFYING	Pretune is identifying process dynamics as a result of a setpoint or output change.
		This process may take up to 4 to 6 process time constants. See Table 7-12
3	CALCULATING	Identification is complete and calculation of new tuning parameters is in process.
		See Table 7-12
4	COMPLETE	Calculations are complete and new parameters are ready to replace the loop's
		tuning parameters, if desired. See Table 7-13

NOTE: While using Pretune, it is recommended that Overshoot Suppression is turned off. With overshoot suppression on, Pretune may not work or may give inaccurate tunings.

Pretune STOPPED menu

Table 7-11 describes the Pretune STOPPED prompts.

Table 7-11 Pretune STOPPED Prompts

Prompt	Range/Selections		Definition
STATUS	This is a read-only prompt.	Status stopped.
PV	This is a read-only prompt.		Current process variable value of the loop being tuned.
OUTPUT	This is a read-only prompt.	Current output value of the loop being tuned.
SETPOINT	This is a read-only prompt.		Current working set point value of the loop being tuned
TUNE SET	Select which set of tuning		If tuning a split loop, set#1 applies to loop output between 0
	parameters (#1 or #2) will		and +100; set#2 applies to loop output between 0 and -100.
	be pretuned and installed.
OPTIMIZE	Select SET PT or LOAD		This optimizes the new tuning parameters according to their
			intended use (that is, controlling changes in setpoint or
			process load).
OVERSHOOT	Select YES or NO.		This determines whether or not some overshoot is
			acceptable in the pretune specified tuning.
			Continued on next page

238 Video Recorder – User Manual