Moisture Measuring Systems Critically Reviewedvon Tolkacz, Martin
doi: 10.1177/002029406900201105pmid: N/A
Until recently, mainly two methods to determine the moisture content of running fibre webs were recognised and in practical use: the measurement of the conductivity of the web and the measurement of the dielectric constant or dielectric losses.For some time paper makers have been able to choose between these and a third method, the so-called infrared system. This is an attempt to compare the measuring characteristics of these three methods and to consider carefully the costs and the results obtained.Let us list first of all the requirements a continuous moisture meter has to meet on a paper-making machine. In addition, the function of the three types of gauges will be briefly explained.
A New Approach to Controlling Thermal ProcessesRoots, William K.; Meeker, Loren D.
doi: 10.1177/002029406900201102pmid: N/A
Roots and Wu (1967) established that meaningful models of common thermal processes (boilers without superheaters, furnaces, ovens, vats, kilns etc.) can be made from a cascade comprising an open-loop gain μ, a transit delay L, and a salient time constant T. They used this model to establish facile procedures for stability determination when such processes were closed-loop controlled. A new procedure is now presented that not only facilitates stability studies but also greatly simplifies transient response determination for all commands and disturbances likely to be encountered by such closed loop controlled processes. This new approach is based on a generalised parameter v that incorporates μ, L and T. Then by means of a new plane, the w plane, displays are presented that readily predict the stability criteria and the transient response for any practical combination of command and disturbance; as is shown by the examples contained in the Appendix. This has radically simplified the control amd instrumentation of the processes with which the authors are associated (induction furnaces, fluidised beds, plasma torches, zone refining, etc.) and the presentation is intended for industrial engineers concerned with the design and control of similar thermal processes.
Tensioned-Wire Length Measuring InstrumentSydenham, P. H.
doi: 10.1177/002029406900201104pmid: N/A
Length measurement using tensioned-wires has been investigated showing that sensitivities of 1 part in 1010 are realistic with stabilities of 1 part in 108 for at least 100 hr periods when detecting small changes of a large nominal length. Wires may also be used to measure continuous lengths from millimetres to decametres with about 4 parts per million repeatability. The existing static theory has been extended to cover dynamic performance and the effect of tensioning-head friction and inertia. Temperature, creep and mechanical hysteretic errors are discussed. A number of specific instruments are described for making a wide variety of dimensional measurements.
Derivation and Application of a Steady Stale Mathematical Model of an Isopropanol-Acetne ReactorHazlerigg, A. D. G.; Poll, A.; Potter, C. J.; Smith, W.
doi: 10.1177/002029406900201103pmid: N/A
As a part of the study of the computer control and optimisation of a pilot scale plant, a mathematical model is derived for the steady-state of the process in which acetone and methyl-isobutyl ketone are made from isopropanol by heterogeneous catalysis in a tubular reactor.Using the model as an analogue computer program, the kinetics of the two reactions involved have been evaluated from results taken from a laboratory reactor. Using these kinetics and the model written as a digital computer program, the behaviour of a pilot-scale reactor has been calculated and this is compared with measured performance.A phase-space analysis of the model is made to illustrate how this technique may be used to predict the expected control characteristics of the process.