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PRESYS
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Instruments
Warning:
Whenever the derivative time (DER) is configured as zero, the auto-tune
algorithm will compute the parameters only for a PI control.
Before carrying out the auto-tune, the user should select the proper control
action (reverse or direct) to meet the requirements of this process.
The auto-tune algorithm is not carried out in the ON/OFF control.
The auto-tune algorithm is carried out regardless of whether the Controllers
are in the automatic or manual mode.
Types of auto-tune
Auto-tune on start-up
The auto-tune procedure on start-up is carried out whenever the controlled
variable is far from its setpoint value, as is usually the case on start-up.
For the user to activate the auto-tune on start-up, he should carry out the
following steps:
i) start by entering the Configuration level 6.
ii) to select the control network where the auto-tune will be carried out (CH-1) or
(CH-2).
iii) to select the ON option for the St.Up parameter (auto-tune on start-up) and press
ENTER.
iv) Note that the Controller's upper display show a flashing TUNE message,
indicating that the auto-tune algorithm is under development. Upon completion of the
auto tune algorithm, the TUNE message disappears from the upper display.
Auto-tune on demand
The on demand auto-tune procedure is carried out whenever the controlled
variable is close to its setpoint value and the system has already achieved its steady
condition. Therefore, before activating the auto-tune on demand make sure both the
controlled variable and the control output are stable.
Whenever the auto-tune on demand is activated, the Controllers start
generating a square wave in their control outputs with an amplitude selected by the
user (D.Out), centered on the output value, in order to cause oscillations on the
controlled process, as illustrated on figure 25. Based on such oscillation the auto-
tune algorithm computes the PID parameters and from that moment on the plant is
controlled by those new parameter values.
D.Out - This is the parameter determining the amplitude of the square wave
generated in the control output for auto-tune computation. The control output will
cause this value to vary for the more and for less from its present output.
DCY - 2057 Pressure Controller
Maintenance
Page 42
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