PR electronics 2286 Bedienungsanleitung Seite 27

Tp are tuned according to the individual process. Before setting the
parameters, the method of regulation directly / inverted must be
determined. Direct controlling results in an active UP relay when the
process value > the setpoint. Inverted controlling results in an active
DOWN relay when the process value > the setpoint.
Inexperienced users may use the following "rule-of-thumb" for
determining the process parameters:
1. The pulse time Tp is set to a value so short that the process value is
barely affected by the supplied energy.
2. Set Xp at max., Ti and Td to 0 (only proportional controlling).
3. Reduce Xp until the process starts oscillating.
4. Increase Xp twofold.
5. Set Ti at max.
6. Reduce Ti until the process starts oscillating again.
7. Increase Ti twofold.
8. If the controller is too slow reaching its setpoint, the differential
controller can be activated. The differentiating function augments the
control signal proportionally to the rise time of the process signal.
Therefore the setting varies according to the process.
002 = PI step controller:
The controller controls motor-driven valves, throttle valves and dosage
units via the UP / DOWN relays by a variable OFF time according to
the difference between the process value and setpoint and to the
selected regulation parameters. The variable parameters are: Xp - the
proportional band, tAU - the exponential average time of the active
relay state - functions as integrating time, tP - the shortest active time
of the relays, nEU - the neutral zone, i.e. the band that the process is to
be kept within, and HSt - the pulse width hysteresis within the neutral
zone.
The PI step controller can be set as follows:
1. The setting method direct / inveted is determined. Direct controlling
results in an active UP relay when the process value > the setpoint.
Inverted controlling results in an active DOWN relay when the process
value > the setpoint.
2. The minimum pulse width tP is set in s. A reasonable start value is
0.5% of the actuating time - the period from closed to open state of
the actuator.
3. The neutral zone nEU is set as the band which the controlling process
is to be kept within. The neutral zone is set in % of the input span.
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003 = 3-point controller:
004 = dI/dt control:
005 = Comparator with an external setpoint:
4. The hysteresis HSt is set in % of the input span. A value of nEU/4 is
a reasonable start value. In processes with large dead times, HSt can
with advantage be diminished.
5. Set the proportional band Xp (hP) to max. = 999% and tAU to max.
= 999 s.
6. Reduce Xp (hP) until the process starts oscillating.
7. Increase Xp (hP) twofold.
8. Reduce tAU until the process starts oscillating.
9. Increase tAU twofold.
The neutral zone, which is set in % of the input span, is placed
symmetrically around the setpoint setting. When the process input is
lower than the neutral zone, the UP relay is activated until the process
input increases to the setpoint value. When the process input is higher
than the neutral zone, the DOWN relay is activated until the process
input decreases to the setpoint value. The setting parameters are SEt
setpoint, nEU neutral zone, dIr direct, and InU inverted. Direct / inverted
reverses the state of the UP / DOWN relays.
The function monitors the size of the decrease or increase (dl) of the
input within a set period of time (dt). A time constant for the input value
can be selected. The limit of the magnitude of the decrease / increase
(dI) is entered in the menus 1.2 and 1.3. The period of time (dt) over
which the change is to be monitored is entered in the menus 1.6 and
1.7. At a positive (dI/dt), the relays will be activated when the change of
the input signal exceeds the value (dI) in menu 1.2 or 1.3 within the set
period of time (dt) in menus 1.6 and 1.7. The relays will be de-activated
when the change is lower than the (dI) minus HS (the hysteresis) per
(dt).
At a negative (dI/dt), the relays will be activated when the change of the
input signal drops below the value (dI) in menu 1.2 or 1.3 within the set
period of time (dt) in menus 1.6 and 1.7. The relays will be de-activated
when the change is larger than the (dI) plus HS (the hysteresis) per (dt).
The process input A is compared with the external setpoint on input B.
When the two signals are within the neutral zone, no relays are active.
When A is smaller than B minus ½ neutral zone, the DOWN relay changes
its state. When A is larger than B plus ½ neutral zone, the UP relay
changes its state. The hysteresis is placed inside the neutral zone.
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