Elsevier

Automatica

Volume 36, Issue 6, June 2000, Pages 815-829
Automatica

Regulation by tables

https://doi.org/10.1016/S0005-1098(99)00209-5Get rights and content

Abstract

A computer-based regulator embodying a trivial background for regulation programmers is pursued. To start, logic is expanded until it incorporates rules and their obligations. Then, theory is withdrawn to rescue tables and interpolations. Finally, the regulator is implemented. It is a governor that follows (tolerant) ruling tables with (multi-) linear interpolations, requires minimal rationale and may govern even with few programmed table lines. For the time being, performance stands on the wisdom of programmers.

Introduction

Regulation tables such as Table 1 may be devised for human operators in charge of a plant.

These tables are very easy to understand. However, people with mathematical training avoid reading them and, when pushed to read, they utter something like: 0.05(qo),115,000(poref)…1.08(x),…0.05…125000…0.72(x)…and so on. Pushed much further, they may finally come up with complete sentences, such as: ifqois 0.05 andporefis 115,000, then x is 1.08; and ifqois 0.05 andporefis 125,000, then x is 0.72; and so on. Here, indicative verb moods provide propositions that reveal some binary logic studies. That explains the initial reluctance since words such as and are defined in binary logic courses by tables which may only be read by using the same (or equivalent) words. Another issue is that one may also read: qois 0.05,porefis 115,000 and x is 1.08; orqois 0.05,porefis 125,000 and x is 0.72; or so on. The problem is that, in the first case, the whole reading seems true when conditions are false (e.g. when qo is 0.26) and, in the second case, it seems false for both the inclusive and the exclusive standard course versions of or. Puzzlement may be amusing and promote the chase of other words such as also to replace and in the first reading (Lee, 1990a). However it does not help much with the regulation of the plant. The key point is that the indicative mood misses the scenario. Regulation is the king's job. Its name comes from rex, the Latin name for kings. It deals with disturbances. Their name comes from turba, the Latin name for mobs. Not in vane, Watt called his fly-ball device a governor. Table 1 is not pictorial, but mandatory; i. e., it is meant to be read as: ifqois 0.05 andporefis 115,000, then let x be 1.08; ifqois 0.05 andporefis 125,000, then let x be 0.72; and so on. This imperative mood has been ignored in logic studies so far and, consequently, has produced elusive manoeuvres against basic grammar (e.g., within fuzzy logic). Let us foster a wider logic in Section 2. Then, let us abdicate and adhere to tables in Section 3. Let us explore applications in Section 4, and let us implement a regulator in Section 5. It will be a rather anthropomorphic governor: not a bright one, but a loyal delegate that will govern by following plain directions.

Section snippets

Logic

A proposition in binary logic (coming from Aristotle) is a pictorial discourse with truth varying within the binary set {0,1}. 0 is read as false there, and 1 as true. When ruling instead of describing, obligation (i.e., binding power) is more important than truth. A rule is a mandatory discourse with obligation also varying within {0,1}, at least at first glance. However, 0 is read as loose now, and 1 as obligatory. There are other differences as well; e.g., global obligation of compound rules

Tolerance

The last corollary in Section 2 almost ends the study on tables such as Table 1. The only pending issue is that of the broadening of pj(x) into pj(x1)∧⋯pj(xM), for 1≤jN. But, before trying to do that, let us think. The study involving one independent variable (x) was tiring and difficulties grow fast when the number of independent variables (x1,…,xN) increases, since more considerations become necessary to analyze propositions and rules, and more alternative cases arise afterwards.

Applications

Let us illustrate the application of a tolerant regulation table by considering an example drawn out of a regulation solution devised for the Polpaico Cement Factory, near Santiago de Chile, by Rojas and Olivares (1993). (Coherent alterations have been made, mostly to honor confidentiality agreements.)

Example (A mixing tank)

Assume a cylindrical tank receiving wet minerals from a grinding mill and industrial water from a deposit, through two different pipes, and pumping the mixture to flotation cells through a third

Implementation

The remaining issue is how to implement a computer-based regulator handling (tolerant) regulation tables with (multi-)linear interpolations, such as Table 4, Table 2. Consider 2 Logic, 3 Tolerance calmly, and see the appendix. Least movement is easy to achieve. (Multi-)linear interpolation may be divided into two stages:

  • The first stage is a sequential search that locates the actual value of each independent variable, xm for m∈{1,…M}, between neighboring values Xm0 and Xm1 in the table which are

Conclusions

Logic has been expanded pursuing a trivial background for control engineers. By dropping theory (tolerant) tables with (multi-) linear interpolations have been brought back to light. Applications have been explored. Also, a regulator with plain routines for helping programmers has been devised. The regulator completes the tables when needed, obeys them and interpolates. Thus, it is a loyal governor that follows plain directions. It is not a bright one for the moment, since failures and

Jaime Gları́a was awarded the professional title of Ingeniero Civil Electrónico (U.T.F.S.M.) in 1975. He is a faculty member in the Department of Electronics at Universidad Técnica Federico Santa Marı́a. His main current research interest lies in SISO process regulation.

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Jaime Gları́a was awarded the professional title of Ingeniero Civil Electrónico (U.T.F.S.M.) in 1975. He is a faculty member in the Department of Electronics at Universidad Técnica Federico Santa Marı́a. His main current research interest lies in SISO process regulation.

R.A. Rojas holds the title of Ingeniero Civil Electrónico awarded by the Universidad Técnica Federico Santa Marı́a (U.T.F.S.M.), Valparaı́so, Chile, in 1974. He later studied at UMIST and the University of Manchester, Manchester, England, where he obtained an M.Sc. in 1980 and a Ph.D. in 1983. Dr. Rojas is at present a faculty member at the Department of Electronics of the U.T.F.S.M. and his technical interests cover modelling, simulation and regulation of industrial processes.

M.E. Salgado was awarded the title of Ingeniero Civil Electrónico (U.T.F.S.M.) in 1974, the M.Sc. degree (Imperial College, London) in 1979 and the Ph.D. degree (University of Newcastle, Australia) in 1989. He is currently a faculty member at the Department of Electronics (U.T.F.S.M.) and his research interests include control system design and system identification.

This paper was not presented at any IFAC meeting. This paper was recommended for publication in revised form by Associate Editor P.J. Fleming under the direction of Editor S. Skogestad.

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