DMCplus控制器主要包含兩種類型的變量。對一被控過程唬复，自變量是指過程的輸入變量矗积，而因變量是過程的輸出變量。
過程輸入變量是指當(dāng)其發(fā)生變化時盅抚，會引起過程發(fā)生相應(yīng)變化的變量漠魏。過程輸出變量是指當(dāng)其發(fā)生變化時，不會影響過程妄均。
比如說柱锹，過程進(jìn)料速率、再沸器蒸汽流量設(shè)定值和環(huán)境溫度等都是過程輸入變量（自變量）丰包。因上述任一變量的變化都會使過程發(fā)生改變禁熏。過程輸入變量既可能是操作員設(shè)定，也可能是不斷變化的干擾邑彪。
塔頂溫度瞧毙、產(chǎn)品雜質(zhì)在線分析器等則是過程輸出變量（因變量）。盡管都可以由操作員所改變寄症，但它們都受到自變量的影響宙彪。
自變量進(jìn)一步分為操作變量(MVs)和干擾變量(DVs)(也被稱作前饋(FF)變量)。MVs是DMCplus控制器所操作的自變量有巧∈推幔可能包括流量控制器設(shè)定點，溫度控制器設(shè)定點篮迎，壓力控制器設(shè)定點等男图。
DVs(也被稱為前饋(FF)變量)是DMCplus控制器不能操作的但會顯著影響過程的自變量示姿。可能包括冷卻水溫度逊笆，進(jìn)料組成及環(huán)境空氣溫度等栈戳。
因變量也被稱為控制變量（CVs）。這些變量由DMCplus控制器控制难裆∽犹矗可能包括產(chǎn)物流質(zhì)量、溫度差牛、壓力命锄、壓差、閥位或其它過程輸出偏化。
盡管CV可以控制在一個固定的設(shè)定點脐恩，但通常它們被控制在上下限之間。這樣DMCplus控制器將有更多空間優(yōu)化過程侦讨。同時還能允許控制器中CVs數(shù)量大于MVs驶冒。
幾乎所有實際過程中，CVs數(shù)都超過MVs韵卤。然而骗污，其中大部分CVs在任意時刻都是不必受約束的。
? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ?圖3：復(fù)雜精餾過程
圖3給出一個復(fù)雜精餾過程例子沈条。這一例子有4個MVs需忿，1個DV和3個CVs，如下所列：
MVs
FIC-2001 ? ? ?塔頂回流量.SP
FIC-2002 ? ? ?塔中產(chǎn)品采出流量.SP
TIC-2003 ? ? ?進(jìn)料溫度.SP
FIC-2004 ? ? ?塔中回流量.SP
DV (FF)
FI-2005 ? ? ? ??塔進(jìn)料流量
CVs
AI-2020 ? ? ? ??塔頂采出產(chǎn)品雜質(zhì)含量
AI-2021 ? ? ? ??塔中采出產(chǎn)品雜質(zhì)含量
AI-2022 ? ? ? ??塔釜采出產(chǎn)品雜質(zhì)含量
該系統(tǒng)是一個強耦合系統(tǒng)蜡歹。改變?nèi)魏我粋€MV都會影響到3個CVs屋厘。改變DV(進(jìn)料流率)也會影響3個CVs。所有5個自變量都是過程輸入月而，3個CVs是過程輸出汗洒。
附原文：
There are two major types ofvariables in a DMCplus controller. Given a process to be controlled, the?independent?variables are inputs to the process and the?dependent variables?are those which are outputs from the process.
Process inputs are thosevariables that when changed, cause a corresponding change in the process.Process outputs are those variables that indicate a change in the process, butcannot affect the process.
Examples of process inputs(independent variables) are feed rate to the process, reboiler steam flow setpoint, and ambient temperature. A change in any of these causes the process tochange as well. Process inputs can either be changed by the operator or theymay be disturbances which change continuously.
Examples of process outputs (dependent variables) are a tower toptemperature and a product impurity analyzer. Neither of these can be changeddirectly by the operator, but both are affected by changes in independentvariables.
The independent variables are further classified as eithermanipulated
variables(MVs) ordisturbance variables(DVs), alsocalled Feed forward (FF) variables. Manipulated variables are those independentvariables which are manipulated by the DMCplus controller. These might includeflow controller set points, temperature controller set points, pressurecontroller set points, etc.
The disturbance variables, also known as feedforward variables, areindependent variables that significantly affect the process, but cannot be manipulatedby the DMCplus controller. These might include the cooling water supplytemperature, feed composition, ambient air temperature, etc.
Dependent variables are also known ascontrolled variables(CVs). These are the variables controlled by the DMCplus controller. Thesemight include product stream properties, temperatures, pressures, differentialpressures, valve positions, or other outputs from the process.
While controlled variables may be controlled to a fixed set point,normally they are controlled between upper and lower limits. This allows theDMCplus controller more room to optimize the process. It also allows acontroller to have significantly more controlled variables than it hasmanipulated variables.
In an actual process, it is nearly always the case that the number ofcontrolled variables exceeds the number of manipulated variables. However, atany given time, most of these controlled variables are not constrained.
The figure above shows an example of a process consisting of a ComplexFractionator. This example has four manipulated, one disturbance, and threecontrolled variables, as listed below:
Manipulated Variables
FIC-2001 ??Top Reflux Flow Controller Set Point
FIC-2002 ??Middle Product Flow Controller Set Point
TIC-2003 ??Feed Temperature Controller Set Point
FIC-2004 ??Middle Reflux Flow Controller Set Point
Disturbance Variables (Feed forward)
FI-2005 ? Tower Feed Flow
Controlled Variables
AI-2020 ??Top Product Impurity
AI-2021
Middle Product Impurity
AI-2022 ??Bottoms Product Impurity
This system is a highly interactive system. Changing any of the four manipulated variables affects all three dependent (controlled) variables.Changes in the disturbance variable (Feed Flow Rate) also affects all three controlled variables. All five independent variables are inputs to the process and all three controlled variables are outputs from the process.
? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ?2015.9.9
