Systemoptimering på ett enkelt sätt - Startprogram för styrenhet från JUMO

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:

• övervakning och dokumentation av inställningsfasen eller den automatiska inställningen.
• generering av en stegvis ändring av börvärdet för att bestämma och registrera reglerkretsens egenskaper utifrån kretsresponsen.
• jämförelse mellan flera olika resultat av reglerkretsar med varierande reglerparametrar.
• stickprovskontroll av styrkretsens kvalitet under produktion eller vid byte av verktyg.
• spara datafiler för att snabbt skicka dem via e-post till en expertgrupp av rådgivare.

Programmet är inte bara användbart, det ger också många andra fördelar - även ekonomiska fördelar - jämfört med konventionell övervakning av processtyrning, till exempel:

• inga ytterligare inspelare eller andra periferiska enheter krävs för driftsättning.
• mycket kort tid krävs för montering och kabeldragning av mätutrustningen.
• ingen anslutning av extra mätutrustning till systemet eller de analoga signalerna från styrenheten.
• stor tidsbesparing tack vare den enkla Plug & Play-gränssnittskabeln.
• en överblick över all viktig processdata.
• simultan dokumentation av system- och/eller driftsättningsdata.

Uppstartsprogram - Driftråd - Exempel: JUMO IMAGO 500

Allmänt om optimering

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.

Regulatorns egenskap/funktionssätt (definitioner/urvalskriterier)

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).

Varför är en 3-stegsregulator olämplig för ställdon?

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.

Vad menas med digitalt ingångsfilter (dF)?

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.

What is meant by 3-state controller?

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

What is meant by modulating controller?

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.

What is meant by cascade control?

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 v_s = 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).

What is meant by contact spacing?

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.

What is meant by reset time?

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.

What is meant by proportional band (Xp1, Xp2)?

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).

What is meant by switching differential/hysteresis?

The switching differential is also referred to as hysteresis and is only relevant for switching controllers with proportional band = 0.
For controllers with inverse operating sense (e.g. heating control), the standard response is as follows:
The switching differential lies below the setpoint. This means that the controller switches off precisely then when the setpoint is exceeded. It only switches on again when the process value has fallen below the switch-on point, which lies below the setpoint by the amount of the switching differential.
On controllers with direct operating sense (e. g. cooling), the switching differential normally lies above the setpoint. As for controllers with inverse operating sense, the switch-off point is precisely at the setpoint. However, it is switched on again above the setpoint, shifted by the amount of the switching differential.

What is meant by actuator stroke time (tt)?

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.

What is meant by proportional controller with integral actuator driver?

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.

What is meant by derivative time?

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

• if the control variable decreases as a result of a disturbance in the process, the D component forms a positive manipulating variable, which counteracts the reduction in control variable.
• if the control variable increases as a result of a disturbance in the process, the D component forms a negative manipulating variable, which counteracts the increase in control variable.
• The damping action increases with the size of the setting for the derivative time (value in seconds).

What is meant by 2-state controller?

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.

What is meant by cycle time (Cy)?

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.

Literature on the subject

• Control Engineering - Basic principles and tips for practitioners