DATALOGIC AUTOMATION - TH-TS series
– INSTRUCTION MANUAL - Rev. 04 - PAGE 4
Please remember that a low value on this parameter reduces the
overshoot while a high value increase it.
1: Value “FuOC” OK
2: Value “FuOC” too high
3: Value “FuOC” too low
4.6 - DOUBLE ACTION PID CONTROL (1rEG - 2rEG)
All the parameters referring to PID control are contained in the group
“
]
rEG”.
The Double Action PID control is used to control plants where there
is an element which causes a positive increase (ex. Heating) and an
element which causes a negative increase (ex. Cooling).
This type of control can be obtained when 2 outputs are
programmed respectively as 1rEG and 2rEG and the par.
“Cont”
=
Pid.
The element causing a positive increase has to be connected to the
output programmed as 1rEG while the element causing a negative
increase has to be connected to the output programmed as 2rEG.
The Double Action PID control works on the outputs 1rEG and 2rEG
depending on the active Set Point
“SP”
and on the instrument’s PID
algorithm with two degrees of freedom.
In order to obtain good stability of the process variable, in case of
fast processes, the cycle times “tcr1” and “tcr2” have to have a low
value with a very frequent intervention of the control outputs.
In this case use of solid state relays (SSR) to drive the actuators is
recommended.
The Double Action PID control algorithm needs the programming of
the following parameters :
"Pb"
– Proportional Band
"tcr1"
– Cycle time of the output 1rEG
“tcr 2”
– Cycle time of the output 2rEG
"Int"
– Integral Time
"rS"
– Manual Reset (if “Int =0 only)
"dEr"
– Derivative Time
“FuOC” -
Fuzzy Overshoot Control
"Prat"
- Power Ratio or relation between power of the element
controlled by output 2rEG and power of the element controlled by
output 1rEG. If par. “Prat” = 0, the output 2rEG is disabled and the
control behaves exactly as a single action PID controller, through
output 1rEG.
4.7 - AUTOTUNING
AND SELFTUNING FUNCTIONS
All the parameters referring to the AUTOTUNING and SELFTUNING
functions are contained in the group
“
]
rEG”.
The AUTOTUNING and SELFTUNING functions permit the
automatic tuning of the PID controller.
The
AUTOTUNING
function permits the calculation of the PID
parameters by means of a FAST type tuning cycle and, at the end of
this operation, the parameters are stored into the instrument’s
memory and remain constant during control.
The
SELFTUNING
function (rule based "TUNE-IN") instead allows
control monitoring and the continuous calculation of the parameters
during control.
Both functions automatically calculate the following parameters :
"Pb"
– Proportional Band
"tcr1"
– Cycle time of the output 1rEG
"Int"
– Integral Time
"dEr"
– Derivative Time
“FuOC” -
Fuzzy Overshoot Control
and, for the Double Action PID control, also :
“tcr 2”
– Cycle time of the output 2rEG
"Prat"
- Ratio P 2rEG/ P 1rEG
To activate the AUTOTUNING function proceed as follows :
Press the T pushbutton, at this point the Auto-tuning function is
activated and is indicated by the flashing led AT/ST.
The regulator carries out several operations on the connected plant
in order to calculate the most suitable PID parameters.
If “Auto” = 1 or “Auto” = 2, and if, at the Auto-tuning start, the
condition for the lower process value is not found (with “Func”
=HEAt) than [SP- |SP/2|] or higher (with “Func” =CooL) than [SP+
|SP/2|], the display will show
“ErAt”
and the instrument will be
swapped to normal control conditions according to the previously
programmed parameters.
To make the error “ErAt” disappear, swap the instrument to the OFF
control (OFF) and then turn it to automatic control (rEG).
The Autotuning cycle duration has been limited to 12 hours
maximum.
If Auto-tuning is not completed within 12 hours, the instrument will
show
"noAt"
on the display
.
In case of probe error, the instrument automatically stops the cycle in
progress.
The values calculated by Auto-tuning are automatically stored in the
instrument’s memory at the end of the correct PID parameters
tuning.
Note :
The instrument is already programmed in our factory to carry
out autotuning at every instrument switch on ("Auto" = 1).
To activate the SELFTUNING function proceed as follows
1) Program par.
"SELF"
= yES
2) Exit from the parameter programming.
3) Connect the instrument to the controlled plant.
4) Activate Self-tuning selecting par.
“tunE”
in the main menu (or by
correctly programming key “U”).
When the Self-tuning function is active, the led AT/ST is permanently
lit up and all the PID parameters ("Pb", "Int", "dEr", etc.) are no
longer visualized.
4.8 - REACHING OF THE SET POINT AT CONTROLLED SPEED
AND AUTOMATIC SWITCHING BETWEEN TWO SET POINTS
(RISE RAMP, FALL RAMP AND DWELL TIME)
All the parameters referring to the ramps functioning are contained in
the group
“
]
rEG”.
It is possible to reach the set point in a predetermined time (in any
case longer than the time the plant would naturally need). This could
be useful in those processes (heating or chemical treatments, etc.)
where the set point has to be reached gradually, in a predetermined
time.
Once the instrument has reached the first Set Point (SP1) it is
possible to have automatic switching to the second Set Point (SP2)
after a set time, thus obtaining a simple automatic thermic cycle.
These functions are available for all the programmable controls (PID
single and double action, ON/OFF and Neutral Zone ON/OFF).
The function is determined by the following parameters :
"SLor"
- Gradient of rise ramp (Process value < Set point)
expressed in unit/minute
"SLoF"
- Gradient of fall ramp (Process value > Set point)
expressed in unit/minute.
"dur.t"
– Dwell time of Set Point SP1 before automatic switching to
Set Point 2 SP2 (expressed in hrs. and min.).
The functions are deactivated when the relative parameters are =
InF.
When the Set Point value is changed or at switch on, the instrument
automatically determines which of the two values “SLor” or “SLoF” it
has to use.
Note:
In case of PID control, if Auto-tuning is desired whilst the ramp
function is active, this will not be carried out until the tuning cycle has
been completed.
It is therefore recommended that Auto-tuning be started avoiding
activating the ramp function and, once the tuning is finished,
deactivate Auto-tuning (“Auto” = OFF), program the desired ramps
and, if it automatic tuning is desired, enable the Self-tuning function.
