How the Logic Works
CELTROL CONTROL STRATEGY
The celtrol control system is very flexible and allows each plant to fine tune control strategies to maximize cell performance. In the following discussion, the control strategies and the numerical values are meant to be typical and not specific to any particular logic employed at any facility. The CELTORL control logic can perform process control functions:
- Automatic Voltage Control (VAC)
- Noise Control
- Tapping Routine
- Anode Set Routine
- Stability Routine
- Alumina Feed Control
- Search Routine
- Starve Routine
- Anode Effect Termination
AUTOMATIC VOLTAGE CONTROL
By mathematically filtering cell voltage over various periods, the calculated smooth cell voltage is compared to the target voltage to determine if an adjustment is needed. An adjustment is needed when the smooth cell voltage falls outside of preset limits around the target voltage. Routines such as Noise Control and Anode Set add temporary voltage to the cell, and the AVC computes these as part of the target cell voltage. A Fixed Voltage set point can be given by supervision through the operator's workstation . This means that the Target Voltage is the Fixed Voltage set point plus any load increase. All other variable set point increments, including the CELTROL panel voltage select switch value, are ignored until the Fixed Voltage set point is taken off through the supervision workstation
NOISE CONTROL
This routine determines if a cell is "noisy" (unstable voltage) by integrating the cell noise resistance over a set time span. If a noisy condition is determined, the cell voltage display will flash the cell voltage. If the cell is found to be "noisy" for three (3) consecutive time periods, the routine will make adjustments to the cell and turn on the "Noise Control" light. If this condition persists after reaching preset maximum voltage in an attempt to stabilize the cell, a "Noisy Too Long" condition is established; the "Noise Control " light will then begin to flash and an audio message will be broadcast to the operators. When the Noise Control routine establishes that the unstable condition has been corrected by its action, it will gradually return the cell to its status prior to becoming too "Noisy". This control routine will hold if the Search routine starts, and it will continue to hold until Search Feed occurs. The Noise Control routine is terminated and the "Noise Control " light turned off whenever a Tapping routine, Anode Set routine, or manual condition is entered.
TAPPING ROUTINE
When selected cells have been pre-initialized by the line supervisory staff through a remote workstation console or through a pre-established computerized schedule, the Tapping routine lowers the anodes during tapping to maintain the cell near target voltage. Additional voltage can automatically be added after tapping as an aid in eliminating the noise created by tapping. This extra voltage will automatically be reduced by the AVC routine over time to return the setpoint to its proper position.
ANODE SET ROUTINE
This routine is also pre-initialized for selected cells by the line supervisory staff through a remote workstation console, and it provides a one-time temporary voltage addition to the cell's target voltage for a programmed time period just after an anode is set. The Anode Set light comes on when the temporary voltage is added. Following the anode setting action, the added voltage is reduced by a preset amount per feed cycle until target set voltage is reached, after which the anode set light will go out. This routine terminates the Search routine; however, the Noise Control routine has precedence over it.
STABILITY ROUTINE
The Stability routine, activated manually, adds a one-time voltage increase to a pot. This voltage is reduced by a variable amount over a variable time length to return the pot to its base voltage. This routine is used to stabilize a pot when normal operation has been disturbed; such as, after tapping the pot, setting anodes, or adding chemicals to the bath. The Stability routine must be enabled through the Enable/Disable Functions function at the operator's workstation. This routine can only be activated once in a given period of time, and the routine won't run if there is any temporary voltage or Noise Control voltage on the pot.
ALUMINA FEED CONTROL
The Alumina Feed Control routine is capable of a wide range of feed and break or punch control for each cell. The feed and/or punch parameters include: Feed time Number of dumps Dump time Number of breaks/punches Punch downtime These parameters are all accessible and can be easily changed by properly authorized personnel. In addition, the four-position rotary switches located on the door of each CELTROL controller allow incremental control at the cell. Base = base feed rate B/2 = half base feed rate O = break/punch only, no feed OFF = no break, punch or feed The normal feed cycles are altered when the Search, Starve or AET routines are in effect.
SEARCH ROUTINE
The Search routine is activated 8 hours (or after some other programmed period) after an anode effect. The routine can also be activated at any time by command through the remote CRT terminals. The routine provides a check against overfeeding, without forcing an anode effect. The Search light will be on when this routine is activated. Search routine is terminated when... Search is complete (demand feed occurs) Tap or Anode Set routines are initiated An anode effect occurs or a Supervisor can terminate this function through the workstation console.
STARVE ROUTINE
The purpose of this CELTROL routine is to get the ore concentration in the cell to a known level. The routine will force an anode effect by extending the feed cycle time. Activation time is variable and is typically set for 48 to 144 hours after an anode effect. The Starve light is on when this routine is in progress. An anode effect will terminate the starve routine. Supervision can also terminate this function through the workstation console.
ANODE EFFECT TERMINATION
The AET sequence is easily variable as to the time intervals and sequence of feed dumps, punches, and anode movements. This routine takes priority over AVC and Feed, but will not operate if Tapping is in progress or the auto/manual switch is in manual. During the AET sequence, a special AVC allows voltage to be brought back to target cell voltage, and normal feed cycle resumes after AET is complete. The AE light is steady during anode effect and flashes if AET is unsuccessful. If the AET sequence is unsuccessful, the CELTROL controller then calls over the audio system for assistance in extinguishing the AE.