1969 Volume 1

The qualities that characterise a great scientist are very elusive. Before I try to deal with them, I would like to clear the air by touching on two points. The first is the very real difference between fundamental and applied science, the first being knowledge oriented and the second project oriented. I want to emphasise right away how strongly I dissent from the view that the one is any way finer or more inspiring than the other.

It seems appropriate at the outset of an introduction to our week’s proceedings to spend a little time drawing attention to the particular characteristics of this series of meetings, the planning of which has now spanned 14 years.

This paper traces the evolution of the theoretical basis of automatic control. The subject is considered from the viewpoint of applications in the process industries, particularly those occurring in papermaking. The emphasis is put on the essential concepts, placing them in the general background of engineering systems analysis. An attempt is made to indicate the mainstream of theoretical developments and to review current practice and the future potential of control technology in the paper industry.

The paper is intended as a tutorial introduction to some of the principles used in model building techniques, which place emphasis on  modelling of the process behaviour as shown to the outside world by records of inputs to and outputs from the process, rather than by attempting to model details of the physics or chemistry internal to the process.

The best way to achieve a well-controlled process is to consider the control during design of the equipment. The steps in designing for control are stated, then expanded in a discussion of the design of flow boxes. An analysis shows how the control of a flow box is affected by the geometry of the box and the characteristics of the air pad supply system.

Automatic controllers have been subjected to fairly intensive theoretical study and some attempts have been made to establish human transfer functions for certain manual control actions. The paper industry is fairly specialised, however, in that the response of the system is very slow. This paper is an attempt to study the human operators’ characteristics in the control of basis weight. The paper is in two parts: the first is an ergonomic study of the process of papermaking and the second is a detailed study of basis weight control. A simulator for basis weight can described that matches the actual operation of the papermachine and has proved extremely useful for training purposes.

The Industrial Democracy Project in Norway is a long-term research sponsored jointly by the Confederation of Employers and the Trades Union Council. The field experiment reported took place in the chemical pulp department of an integrated papermill as one of a series of four experiments carried out in different industrial settings. Extensive task fragmentation and bureaucratisation in modern industry have produced widespread feelings of alienation in the work force, owing to an increasing mismatch between technologically based task requirements and human needs. Emerging theories of socio-technical systems, including a list of psychological job requirements, offers a frame of reference for understanding these problems. Previous experience suggests that full commitment to productive aims can be achieved only under conditions that allow for a high level of self-regulation and learning. In process technology (including pulp and paper), the dependence relationships among the state characteristics of the materials form a complex network. In the present case, this resulted in uncontrolled variations being transmitted along the process. Having identified the optimum unit for experimentation, individual jobs were redesigned in order to facilitate group learning, which would permit the work groups to increase their control of the process. Results of the socio-technical analyses before and after the experiment are reported and reference is made to the variance matrix technique.

I should like to amplify the title of this session . The papers we shall hear deal with the principles of the connection between measurement on the one  hand and computer control on the other and the assumption that the measuring  subsystems are accurate and reliable . The programme committee realises  the importance of measurement per se, but has considered the subject too  large to be included in this symposium.

It is often the case that the output of a measuring subsystem is a fairly strong function of variables other than the one that the system is intended to measure, a fact that should be kept in mind.

This paper reviews some of the problems in the interpretation of measurements of papermaking process variables . It is directed to papermakers or scientists who are not specialists in this field. The viewpoint is that of a statistician.

The main problem discussed is the analysis of continuous signals from process instruments, in so far as they are affected by the papermaking system . Specific hardware problems are not considered. Sampling problems for control are also discussed.

Sampled data can arise in several ways-for example, from manual samples taken from the process at reel change, from discontinuous instruments such as scanning basis weight gauges, also from digital computer control. Sampled data in contrast with continuous data have the problem of how sampling  should be carried out. This is discussed in relation to the spectral characteristics of the variable. The superiority of sampled data control for dead time processes and the relation between sampled data control and statistical quality control are mentioned.

Sampled data control system analysis and synthesis is introduced. The z-transform and modified z-transform are included.

Direct digital control is introduced, using sampled data forms as well as PID analog controller replacement. The relative features of pulse amplitude, pulse width and of velocity and positional algorithms are reviewed, also the selection of the sampling interval. A few of the applications to pulp and paper are reviewed.