在應用DMCplus技術的過程中，我們發現有兩種類型的變量可以被當作斜坡變量控制：真實的斜坡和“偽斜坡”。
真實斜坡，或積分型變量，是對應于材料或能量失衡的。最常見的真實斜坡變量是容器液位。
偽斜坡變量事實上是穩態時間非常長的穩態型變量，以至于在DMCplus控制器中被視為斜坡型。最常見的是高純精餾塔中的分析儀或溫度。這里的困難是相對于干擾的頻率，穩態時間非常長。將變量當做斜坡對待可以有更快的執行頻率。實際上在我們感興趣的時間里，所述變量的作用類似于斜坡，即使其最終會達到穩態。
DMCplus提供了允許程序失衡的能力。在實施斜坡型變量控制器時，這種能力的提供需要對控制器進行一些額外的照顧。
真實斜坡型變量必須處理得非常保守。容器排空可能會使泵燃燒起來，相反容器溢滿則可能會毀壞一臺壓縮機。真實的斜坡必須明確地被控制，并且必須配置為對應用非常關鍵。即使在限制之間，整定Equal Concern Error值也不能過大，否則可能會引起權重為0。
然而偽斜坡處理起來就不會這么保守。盡管穩態優化總試圖平衡偽斜坡，但如果不能，DMCplus控制器仍將盡可能持續運行由控制工程師所定義的MXNIMB周期數。不同于傳統斜坡，當穩態優化不能平衡斜坡時，系統不會為了確認其是否觸碰到任何上下允許失衡目標而對失衡進行檢查。
如前所述，事實上偽斜坡是具有長穩態時間的穩態變量；在控制器感興趣的時間里，變量作用像一個斜坡。
在控制器中這些變量都被當作斜坡型。盡管偽斜坡必須得到明確控制，但它們并沒有被聲明為對應用程序關鍵。參數MXNIMB用于指示是否容忍任何失衡周期。
偽坡道允許指定周期數緩和失衡與真實斜坡是不同的，前者不檢查是否觸碰允許失衡限制。如果穩態優化無法平衡偽斜坡，并且沒有超過最大失衡周期數，則賦予偽斜坡的設定值如圖25傳統失衡斜坡所示。
DMCplus動作計算設定點是一條以當前值為起點，斜率為穩態計算失衡值的延伸向未來的射線。即使當前值在操作限之外，這也是真實的。
注意：真實的斜坡不應該被定義為偽斜坡。真實斜坡的額外檢查對防止容器滿溢或干燥運行非常重要。
附原文：
In the course of applying the DMCplus technology, we have found two types of variables which can be controlled as ramps; the true ramps and "pseudo-ramps."
True ramps, or integrator type variables, are those that correspond to an imbalance of material or energy. The most common true ramp variable is a level in a vessel.
Pseudo-ramps are true steady-state type variables whose time to steady state is very long, that are treated like ramps in the DMCplus controller. These are most commonly analyzers or temperatures in high purity distillation towers. The difficulty here is that the time to steady state is very long, relative to the frequency of disturbance. Treating the variable like a ramp allows a faster execution frequency. In effect, over the time of interest, the variable acts like a ramp even though it eventually will come to steady state.
DMCplus provides the ability to allow a programmed imbalance. This ability provides but requires some additional care in implementing controllers with ramp type variables.
True ramp type variables must be handled very conservatively. Emptying a vessel can burn up a pump, or overfilling a vessel can destroy a compressor. True ramps must be explicitly controlled, and must be configured as critical to the application. Equal Concern Error values for tuning cannot be so large as to cause a zero weight,even between limits.
Pseudo-ramps are not handled quite so conservatively. Although the steady-state optimization attempts to balance the pseudo-ramp, if it cannot, DMCplus control will continue for as many cycles as are specified by the control engineer in MXNIMB. Unlike Traditional Ramps, the imbalance is not checked against any upper or lower allowed imbalance target, in the event that the steady-state optimization cannot balance the ramp.
As mentioned previously, pseudo ramps are really steady-state variables with very long steady-state time; over the time period of interest to the controller, the variable acts like a ramp.
As far at the controller is concerned, these variables are treated like ramps. While pseudo-ramps must be explicitly controlled, they do not have to be declared critical to the application. The parameter MXNIMB is used to indicate whether any imbalanced cycles will be tolerated.
A pseudo-ramp with a moderate?imbalance allowed for a specified number of cycles differs from a true ramp in?that no checking is done against allowed imbalance limits. If the steady-state?optimization is unable to balance the pseudo-ramp, and the maximum number of?imbalanced cycles has not been exceeded, then the pseudo-ramp is given a?setpoint as shown in Figure 25 in?Traditional?Ramps with Imbalance.
The DMCplus move calculation setpoint is a line starting at the current value and extending into the future with a slope equal to the steady-state calculated imbalance. This is true even if the current value is outside the operating limits.
Caution:True ramps should never be defined as pseudo-ramps. The extra checking on true ramps is extremely important in preventing vessels from overfilling or running dry.
? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? 2015.10.7
