13
1: Value “FuOC” OK
2: Value “FuOC” too high
3: Value “FuOC” too low
4.5 – DOUBLE ACTION PID CONTROLLER (1rEG - 2rEG)
All the parameters referred to the PID control are contained into the group
“
]
rEG”.
The Double Action PID control is used to control plants where there is an element which causes a positive increment (ex.
Heating) and an element which causes a negative increment (ex. Cooling).
This type of control is obtainable 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 degree of freedom.
In order to obtain a 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 it’s recommended to use solid state relays (SSR) to drive the actuators.
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.
Whenever par. “Prat” = 0, the output 2rEG is disabled and the controller behaves exactly as a single action PID controller,
through output 1rEG.
4.7 - AUTOTUNING
AND SELFTUNING FUNCTIONS
All the parameters referred to the AUTOTUNING and SELFTUNING functions are contained into the group
“
]
rEG”.
The AUTOTUNING and SELTUNING functions permit the automatic tuning of the PID controller.
The
AUTOTUNING
function permits the PID parameters calculation through a tuning cycle FAST type and, at the end of this
operation, the parameters are stored into the instrument’s memory and remain constant during the control.
The
SELFTUNING
function (rule based "TUNE-IN") permits instead the control monitoring and the continuous calculation of
the parameters during the control.
Both functions automatically calculate the following parameters :
"Pb"
– Proportional Band
"tcr1"
– Cycle time of the output 1rEG
“tcr 2”
– Cycle time of the output 2rEG
"Int"
– Integral Time
"dEr"
– Derivative Time
“FuOC” -
Fuzzy Overshoot Control
and, for the Double Action PID control, also :
"Prat"
- Ratio P 2rEG/ P 1rEG
