Modeling and control of a resistometer with a microcomputer /c James E. Hackney

Microcomputer control, as an extension of direct digital control (DDC), is currently finding application in many laboratory research programs. One such application is in the Resistivity Laboratory in the Department of Chemical, Metallurgical, and Polymer Engineering at The University of Tennessee, Knoxville where a PDP-11 microcomputer is to replace a PDP-15 minicomputer. The computer is used for data acquisition and temperature control of a resistometer: a device that measures the electrical resistivity of a sample as a function of temperature.

This study was a specific application of DDC to the resistometer for a Ni₄Mo sample. The study involved both the computer simulation and modeling of the system as well as the development of a viable temperature control algorithm using advanced control techniques. The study concluded that a feedforward-feedback control scheme was sufficient for proper control. The feedforward element was taken to be a model of the system based upon a heat balance, and the feedback element was the discrete approximation to the PI controller. Two feedback controllers were used: a temperature PI controller for isothermal regimes and a rate controller for heating or cooling regimes. Overall, the control eliminated any appreciable overshoot and achieved control in the isothermal regime.