Honeywell VRX180 Manual De Usuario

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. 

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.  

Table 7-11 describes the Pretune STOPPED prompts. 

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 
parameters (#1 or #2) will 
be pretuned and installed. 

If tuning a split loop, set#1 applies to loop output between 0 
and +100; set#2 applies to loop output between 0 and -100. 

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. 

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