Vanliga frågor och svar om grunderna, uppstart och produkterna Kompaktregulator JUMO dTRON 16.1, JUMO cTRON, flerkanalig process- och programregulator JUMO IMAGO 500, Processregulator JUMO DICON 400, 500, 501 och regulatorn JUMO dTRON 304/308/316
Styrenheter som JUMO IMAGO 500, JUMO DICON 500 och nu även den nya JUMO dTRON-serien innehåller ett särskilt programvaruverktyg i inställningsprogrammet för övervakning och dokumentation av driftsättningen, vilket gör den betydligt enklare.
Denna startprogramvara gör det möjligt att visualisera och lagra analoga och binära signaler medan systemet optimeras.
Särskilt för komplexa processer är en visuell presentation i realtid av de viktigaste processdata praktiskt taget oumbärlig för styrteknikern.
Allt du behöver för systemoptimering är en av de styrenheter som nämns ovan, en dator med inställningsprogrammet och en gränssnittsanslutning via en inställningskabel med RS232- eller USB-gränssnitt. Denna anslutning är nödvändig i vilket fall som helst för inställningsprogrammeringen, och är därför vanligtvis tillgänglig.
Viktiga inställningar, t.ex. fritt val av signaler för att visa de enskilda analoga och binära värdena i instrumentet, zoom, olika utskriftsalternativ, visa eller dölja enskilda kurvor, fri skalning och val av färger ingår alla som standard i detta programvaruverktyg.
Programmets viktigaste funktioner omfattar:Programmet är inte bara användbart, det ger också många andra fördelar - även ekonomiska fördelar - jämfört med konventionell övervakning av processtyrning, till exempel:
Regleroptimering (eller inställning) är justeringen av regulatorn för en specifik process eller reglerkrets. Reglerparametrarna måste väljas så att den mest gynnsamma responsen för reglerkretsen uppnås under de givna driftsförhållandena. Detta optimala svar kan dock definieras på olika sätt, t.ex. att nå börvärdet snabbt, med en liten överskridning, eller en något längre stabiliseringstid utan överskridning. Om allt som förväntas av regulatorn är ett svar som för en gränskontakt (utan pulsdrift) finns det inget behov av att hitta de optimala inställningarna för proportionellt band, derivattid eller återställningstid. Det är endast kopplingsdifferentialen som måste fördefinieras.
I de flesta fall kan styrenheten själv bestämma styrparametrarna genom funktionen för självoptimering (autotuning), om processen tillåter självoptimering. Alternativt kan den optimala parameterinställningen bestämmas "manuellt" genom experiment och empiriska ekvationer (se formlerna i tillägget).
När styrenheter byts ut, eller med identiska styrinstallationer, kan styrparametrar också accepteras eller anges direkt.
Efter en manuell parameterinställning får autotuning inte längre startas, eftersom detta skulle skriva över inställningarna.
Formler för inställning enligt pendlingsmetoden:
Controller action |
|
P | XP = XPk / 0,5 |
PI | XP = XPk / 0,45 T P = 0,85 ·TK |
PID | XP = XPk / 0,6 Tn = 0,5 · TK Tv = 0,12 · TK |
Formler för inställning enligt stegrespons:
Controller action | Control loop | Error |
P | XP = 3,3 · KS · (Tu/Tg) · 100 % | XP = 3,3 · KS · (Tu/Tg) · 100 % |
PI | XP = 2,86 · KS · (Tu/Tg) · 100 % T n = 1,2 · Tg |
XP = 1,66 · KS · (Tu/Tg) · 100 % T n = 4 · Tu |
PID | XP = 1,66 · KS · (Tu/Tg) · 100 % T n = 1 · Tg T v = 0,5 · Tu |
XP = 1,05 · KS · (Tu/Tg) · 100 % T n = 2,4 · Tu T v = 0,42 · Tu |
Omvänt: Regulatorns utgång Y är större än 0, eller reläet aktiveras när processvärdet är mindre än börvärdet t.ex. uppvärmning).
Direkt: Regulatorns utgång Y är större än 0, eller reläet aktiveras när processvärdet är större än börvärdet (t.ex. kylning).
Den modulerande regulatorn har liksom 3-stegsregulatorn, två växlande styrutgångar, vilka dock är särskilt utformade för motordrivna manöverdon, t.ex. för öppning eller stängning.
m det krävs en kontinuerlig utsignal för 3-stegsregulatorn för att upprätthålla en viss utgångsnivå, kan vi se att i fallet med den modulerande regulatorn kommer den elektriska ställdonsdriften att stanna kvar i det läge som uppnås när det inte finns någon ytterligare signal från regulatorn.
På så sätt kan manöverdonet till exempel förbli 60 % öppet även om det inte styrs av regulatorn i detta ögonblick.
Det digitala ingångsfiltret (dF) dämpar ingångssignalerna och påverkar både indikering och styrenhet. Ju större värde för "dF",
desto större är dämpningen av insignalen. Ett extremt högt eller lågt värde kan ha en negativ inverkan på reglerkvaliteten. I de flesta fall kan standardinställningen för "dF" användas för driften.
3-state controllers have two outputs which may be either switching or
continuous (relay contact or e.g. 4 - 20 mA). 3-state controllers are
used if the control variable has to be or can be influenced through two
actuators with opposing action.
This may be a climatic cabinet with
a thyristor power unit for the electric heating and a solenoid valve
for cooling. In this example, a 3-state controller with a continuous
(analog) output for the heating function (controller output 1) and a
switching output for the cooling function (controller output 2) would be
the best choice.
On 3-state controllers, the parameters
proportional band, reset time, derivative time and hysteresis, familiar
from 2-state controllers, can often be set separately for both operating
senses. The 3-state controller additionally features the parameter
Modulating controllers have two switching outputs and are especially
designed for operating actuator drives which can, for instance, open or
close a flap valve.
Actuators/actuator drives that can be operated:
AC motor actuators, DC motors, 3-phase motor actuators, hydraulic cylinders with solenoid valves etc.
Cascade control can significantly improve the control quality. This applies in particular to the dynamic action of the control loop, in other words, the transition of the process variable following setpoint changes or disturbances.
Example 1: schematic construction of a cascade
Chocolate has to be heated to vs = 40 °C for processing. The chocolate temperature must nowhere exceed 50 °C (even close to the heater). It is therefore heated on a water bath.
Cascade control is used in order to achieve rapid stabilisation.
Controller 1 is always the master controller, controller 2 always the slave.
The setpoint for the slave controller is produced by output conversion.
The control output y1 is converted to a setpoint using the unit of the process value x2 (here: 0 - 100 % = 0 - 50 °C).
List of symbols
O2 - Output 2
I1 - Analogue input 1
I2 - Analogue input 2
C1 - Controller 1
C2 - Controller 2
w
1 - Setpoint controller 1
w
2 - Setpoint controller 2
x
1 - Process value controller 1
x
2 - Process value controller 2
x
w1 - Deviation controller 1
x
w2 - Deviation controller 2
y
1 - Control output 1
y
2 - Control output 2; output 1 of controller 2
v
s - Chocolate temperature
v
w - Water bath temperature
Example 2: construction of a trimming cascade
Two charges of chocolate have to be heated to 40 °C and 50 °C. The chocolate temperature must nowhere (not even close to a heater) exceed the setpoint by more than 10 °C. It is therefore heated on a water bath.
Trim cascade control is used to achieve rapid stabilisation without overshoot and without altering the controller configuration (output conversion) at a change of setpoint (batch change).
Controller 1 is always the master controller, controller 2 always the slave controller.
The setpoint for the slave controller is produced by output conversion and the addition of the master controller setpoint (w1).
In setpoint conversion, the control output y1 is converted to a value with the unit of the process value w2. It corresponds to the maximum permitted temperature difference (± | x1 - w1 |; here: 0 - 100 % = -10 to +10 °C).
List of symbols
O2 - Output 2
I1 - Analogue input 1
I2 - Analogue input 2
C1 - Controller 1
C2 - Controller 2
w1 - Setpoint controller 1
x1 - Process value controller 1
x2 - Process value controller 2
xw1 - Deviation controller 1
xw2 - Deviation controller 2
y1 - Control output 1
y2 - Control output 2; output 1 o controller 2
vs - Chocolate temperature
vw - Water bath temperature
If the process variable varies within a fixed interval about the
setpoint - the contact spacing Xsh - then neither of the outputs is
active. Exception: 3-state controllers with I and D components. Within
the contact spacing, only the proportional component is inactive.
This contact spacing is necessary to prevent continual switching
between the two manipulating variables, e.g. heating and cooling
registers, when the control variable is unsteady. The contact spacing
is also commonly called the dead band. Too small a dead band can lead
to a pointless waste of energy in a plant.
The I component of the controller output signal has the effect of continuously altering the manipulating variable, until the process value has reached the setpoint.
As long as the control deviation is present, the manipulating variable is integrated upwards or downwards. The longer the control deviation continues to be present in a controller, the larger the integral effect on the manipulating variable. The larger the control deviation and the smaller the reset time, the more pronounced (faster) the effect of the I component.
The I component ensures stabilization of the control loop without permanent control deviation. The reset time is a measure of the effect the control deviation duration has on the control action. A larger reset time means that the I component is less effective and vice versa. Within the specified time Tn (in sec.), the change in the manipulating variable that is produced by the P component (xp or pb), is added once more. Accordingly, there is a fixed relationship between the P and the I component. A change in the P component (xp) also means a changed time response, at a constant value for Tn.
In a purely proportional controller (P controller) the manipulating variable (controller output Y) is proportional to the control deviation within the proportional band (Xp). The gain of the controller can be matched to the process by altering the proportional band. If a narrow proportional band is chosen, a small deviation is sufficient to achieve a 100 % output, i.e. the gain increases as the proportional band (Xp) is reduced. The reaction of the controller to a narrow proportional band is faster and more pronounced. A proportional band that is too narrow will cause the control loop to oscillate. Any alteration of the proportional band will also affect the I and D action of a PID controller to the same extent.
If the proportional band is set to zero, the controller action
is ineffective. This means that the controller operates solely as a
limit contact. The selected hysteresis or switching differential is
effective, the settings for the derivative time and the reset time,
however, are not taken into account.
For all controller types, except for the 3-state (double-setpoint)
controller, only the proportional band Xp1 is relevant. With 3-state
controllers only, separate settings for the proportional band (for both
operating senses) are necessary (e. g. Xp1 for heating and Xp2 for
cooling).
Die Schaltdifferenz wird auch als Hysterese bezeichnet und ist nur bei schaltenden Reglern mit Proportionalbereich = 0 relevant.
Für Regler mit inversem Wirksinn (z. B. Heizungsregelung) gilt für das standardmäßige Verhalten folgender Zusammenhang:
Die Schaltdifferenz liegt unterhalb des Sollwertes. Das bedeutet, der Regler schaltet genau beim Überschreiten des Sollwertes ab. Das erneute Einschalten erfolgt erst, wenn der Istwert unter den Einschaltpunkt gesunken ist, der um den Betrag der Schaltdifferenz unterhalb vom Sollwert liegt.
Bei Reglern mit direktem Wirksinn (z. B. Kühlung) liegt die Schaltdifferenz standardmäßig oberhalb des Sollwertes. Der Ausschaltpunkt liegt wie beim Regler mit inversem Wirksinn genau auf dem Sollwert. Das Wiedereinschalten erfolgt jedoch, um die Schaltdifferenz verschoben, oberhalb des Sollwertes.
The actuator stroke time is a variable provided by the actuator drive
and is therefore only relevant for modulating controllers or
proportional (continuous) controllers with integral actuator driver.
The time that the actuator drive takes to travel once across the full
usable manipulation range is set under actuator stroke time.
The actuator stroke time cannot be determined by self-optimization (autotuning). It must always be set before the optimization.
The actuator stroke time provides the controller with information about
the effect of the actuating pulses. At an actuator stroke time of 20
seconds, for example, the percentage change in manipulating variable, at
the same actuating pulse, is significantly larger than for an actuator
with 100 seconds stroke time, for example.
When selecting or dimensioning actuator drives, it must be taken into
account that a short stroke time of, say, less than 10 seconds will
result in large steps of the manipulating variable, and consequently to a
reduced control accuracy. If, for example, we assume that 0.5 seconds
is the shortest actuating pulse time, a stroke time of 10 seconds would
result in only 20 actuating steps. This would mean that the manipulating
variable can only be changed in 5 % steps.
Actuator drives with a very long stroke time can, however, be
disadvantageous as far as the dynamics is concerned, because the
manipulating variable can only be changed relatively slowly by the
control action. In actual operation, however, problems arising from
stroke times that are too short occur more frequently than those caused
by stroke times that are too long.
The short form "actuating controller" is used to describe a "proportional controller with integral actuator driver". In contrast to the modulating controller, an actuator feedback signal is essential for the actuating controller.
The actuating controller controls the clockwise or anticlockwise movement of the motorized actuator via 2 switching outputs.
The position of the motorized actuator is registered and compared with the manipulating variable (yR) of the proportional controller.
The intensity of the D component (differential component) can be set via the derivative time. The D component of a controller with PID or PD action reacts to the rate of change of the process value.
When the setpoint is approached, the D component acts as a brake, thereby preventing the control variable from overshooting the setpoint.
Basically, the D component has the following effects:
As soon as the control variable changes, the D component reacts against this change.
For a controller with an inverse operating sense (i.e. for heating) this would mean, for example
The 2-state controller (ON/OFF controller) switches the output when the
setpoint is reached. If the value falls below the setpoint by a
certain adjustable tolerance (xsd, switching differential, hysteresis),
then the output is switched on again. It therefore only has two
switching states. It is used in temperature control applications where
the heating or cooling is only switched on or off.
A 2-state controller with dynamics can, however, also operate with a P, I, or D component.
The switching cycle time is quoted in seconds and defines the period during which a full switching cycle consisting of switch-on and switch-off times takes place.
Generally, the cycle time should be selected so that the actual control process can still be smoothed out. At the same time, the switching frequency must always be taken into account.
The response can best be reset in manual mode so that the direct influence of the manipulating variable on the cycle time can be monitored. With a manipulating variable of 50 %, "Ton" and "Toff" are equal. If the manipulating variable is altered, this ratio alters accordingly.