在应用DMCplus技术的过程中，我们发现有两种类型的变量可以被当作斜坡变量控制：真实的斜坡和“伪斜坡”。
真实斜坡，或积分型变量，是对应于材料或能量失衡的。最常见的真实斜坡变量是容器液位。
伪斜坡变量事实上是稳态时间非常长的稳态型变量，以至于在DMCplus控制器中被视为斜坡型。最常见的是高纯精馏塔中的分析仪或温度。这里的困难是相对于干扰的频率，稳态时间非常长。将变量当做斜坡对待可以有更快的执行频率。实际上在我们感兴趣的时间里，所述变量的作用类似于斜坡，即使其最终会达到稳态。
DMCplus提供了允许程序失衡的能力。在实施斜坡型变量控制器时，这种能力的提供需要对控制器进行一些额外的照顾。
真实斜坡型变量必须处理得非常保守。容器排空可能会使泵燃烧起来，相反容器溢满则可能会毁坏一台压缩机。真实的斜坡必须明确地被控制，并且必须配置为对应用非常关键。即使在限制之间，整定Equal Concern Error值也不能过大，否则可能会引起权重为0。
然而伪斜坡处理起来就不会这么保守。尽管稳态优化总试图平衡伪斜坡，但如果不能，DMCplus控制器仍将尽可能持续运行由控制工程师所定义的MXNIMB周期数。不同于传统斜坡，当稳态优化不能平衡斜坡时，系统不会为了确认其是否触碰到任何上下允许失衡目标而对失衡进行检查。
如前所述，事实上伪斜坡是具有长稳态时间的稳态变量；在控制器感兴趣的时间里，变量作用像一个斜坡。
在控制器中这些变量都被当作斜坡型。尽管伪斜坡必须得到明确控制，但它们并没有被声明为对应用程序关键。参数MXNIMB用于指示是否容忍任何失衡周期。
伪坡道允许指定周期数缓和失衡与真实斜坡是不同的，前者不检查是否触碰允许失衡限制。如果稳态优化无法平衡伪斜坡，并且没有超过最大失衡周期数，则赋予伪斜坡的设定值如图25传统失衡斜坡所示。
DMCplus动作计算设定点是一条以当前值为起点，斜率为稳态计算失衡值的延伸向未来的射线。即使当前值在操作限之外，这也是真实的。
注意：真实的斜坡不应该被定义为伪斜坡。真实斜坡的额外检查对防止容器满溢或干燥运行非常重要。
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
