Red-lion PCU Manuel d'utilisateur télécharger pdf (Page 20)

OPERATION OVERVIEW

CONTROLLER POWER-UP

Upon applying power, the controller delays control action and process

indication for five seconds to perform several self-diagnostic tests and

displaybasic controller information. Initially, the controller illuminates both

displays and all annunciators to verify that all display elements are

functioning. The controller then displays the programmed input type in the

main display. Concurrently, it displays the current revision number of the

operating system software in the bottom display. The controller checks for

correctinternaloperation anddisplays an errormessage (E-XX) ifan internal

fault is detected (see Troubleshooting, page 73, for further information).

Upon completion of this sequence, the controller begins control action by

displaying the process value and updating the outputs based upon the PID

control calculation.

CONTROLLER POWER DOWN

At power down, the steady state control value as well as all parameters and

control modes are saved, to provide a quick and predictable process response

on the next power-up.

When powering down the process, it is important to power down the

controller at the same time. This prevents the reset action of the controller

from shifting the proportional band while the process signal is dropping and

prevents excessive overshoot on the next process start-up.

PROCESS START-UP

After starting the process, the controller’s PID settings must be initially

“tuned” to the process for optimum control. Minimal tuning consists of

adjusting the Proportional Band, Integral Time, and Derivative Time

parameters to achieve the optimum response to a process disturbance. The

controller can be tuned once, but must be re-tuned if the process has been

changed significantly. Several options exist for tuning these parameters:

A)Usethecontroller’sbuilt-inAuto-Tunefeature(seeAuto-Tune,page64).

B) Use a manual tuning technique (see Manual Tuning, page 76).

C) Use a third party tuning software package (generally expensive and not

always precise).

D) Use values based on control loop experience, calculated values or values

from a similar process.

If the controller is a replacement, the PID settings from the unit being

replaced may be used as good initial values. Be sure to consider any

differencesin the units and the PID settings when replacing. The PID settings

maybefine tuned by using the techniques outlined in the PID Control section.

Aftertuningthe controller totheprocess, it isimportantto power theloadand

the controller at the same time for best start-up response.

MANUAL (USER) & AUTOMATIC OPERATION

The controller can be transferred between Automatic control (closed

loop; PID or ON/OFF control) and Manual control (open loop). In the

Hidden Function Mode, the “trnf” parameter allows the operator to select

thedesired operating mode. To allow front panelswitching betweencontrol

modes, program the transfer (trnf) parameter to “Enbl” in the Lockout

Module.The user input or RS485 serial interface option may also be used to

perform the auto/manual transfer function, independent of the setting in the

Lockout Module.

Manualoperationprovides direct control of the output(s) from 0 to +100%,

or -100% to +100% if the secondary output is installed. For Valve Positioner

models with slidewire feedback, this mode allows manual valve positioning.

TheMAN(REMforRemoteSetpointmodels)annunciatorflashestoindicate

that the unit is in manual operation.

When transferring the controller mode from/to automatic, the control

power output(s) remain constant, exercising true “bumpless” transfer. When

transferringfrom manual to automatic, the power initially remains steady but

integral action corrects (if necessary) the closed loop power demand at a rate

proportional to the Integral Time. The programmable high and low power

limit values are ignored when the unit is in manual operation.

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Red-lion PCU Manuel d'utilisateur Page 20

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