FACTS Engineering Direct Logic 405, Руководство пользователя

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PID FUNDAMENTALS 5.2
LOOP OPERATING MODES
The Temperature Controller operates in one of two modes, either PID or ON/OFF control.
PID Control
In PID Control mode, the Temperature Controller initially computes and controls the outputs based on
the programmed PID parameters stored in V-Memory. These parameters are normally calculated during
the Auto Tuning process. All alarms limits are continually monitored.
ON/OFF Control
In ON/OFF Control mode, the Temperature Controller outputs turn on and off based on only the Process
Temperature, Set Point, ON/OFF Hysteresis, and control type either heating or cooling.
LOOP ALGORITHM
This section describes the PID algorithm used by the Temperature Controller.
Loop Variables
All loop calculations are performed using normalized Reals. A normalized Real is a floating point
number in the range of 0.0 to 1.0. High precision is maintained since the floating point calculation is
carried out to eight significant digits. The output from the loop is converted from a normalized Real to
either a 12-bit number, 0-4095, or the amount of output 0-100.0%.
PID Control
The Temperature Controller provides feedback loops using the PID (Proportional-Integral-Derivative)
algorithm. The controller Output is computed from the measured process variable (temperature) as
follows:
Let
Kc = Proportional gain.
Ti = Reset or integral time.
Td = Derivative time or rate.
SP = SetPoint.
PV(t) = Process Variable (temperature) at time "t".
e(t) = SP - PV(t) = PV error (deviation from SetPoint at time "t")
Then
M(t) = Controller output at time "t"
M t Kc e t
Ti
E x dx Td
d
dt
e t M
o
t
( ) ( ) ( ) ( )
= + +





 +
∫
1
0