ATC770 Microprocessor-Based Pressure/Process Controller 15
2.11 CONTROL AND RETRANSMISSION OUTPUTS COMMON SPECIFICATION
Reference Accuracy: ±0.1% of output span @ 25 ± 10°C and nominal line voltage.
Linearity Error: <0.1% of output span.
Output Noise: <0.1% of output span.
2.12 CONTROL ALGORITHM SPECIFICATION
Control Type: PID plus Integral Preload plus Anti-Reset Windup
Output Value Indication: Selectable between the following Modes:
• Range 0 / 100.0%
• Selectable with two calibrated values for RPM indication
• In automatic mode either mode is available
• In manual mode, a parameter is provided to select the first or second method of indication.
SMART Algorithm: The SMART procedure is activated by setting the SMART Parameter to ON. In
manual mode the controller will start the TUNE algorithm (SMRT led flashes), while in automatic
mode it will enable the ADAPTIVE function (SMRT led lights steady).
The SMART can select two types of procedures:
1. The TUNE algorithm
2. The Adaptive algorithm
1. TUNE ALGORITHM
To implement the TUNE algorithm, set the instrument in manual mode and the select SMART ON.
SMART will switch to OFF after the PID parameters (PB, TI, TD) are calculated (during this
procedure the LED will be flashing). The basic concepts of the auto-tuning system are based on the
open loop step response, for this reason the TUNE function may be activated only in the manual
mode.
The equivalent mathematical model of the process is characterized by three parameters: the gain,
the time constant and the equivalent time delay. The power output of the controller is changed by a
small step value. Then, the controller stores the process variable response. From the transient
response, the controller estimates the three basic process parameters by means of the area’s method.
It applies these parameters, and re-runs the step process. When this is done, it calculates the final
PID parameters.
The step response is a convenient way to characterize this type of process dynamics because its
model is based on the alteration of the behavior of the process and very accurately determining the
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