Microprocessor-based PID controller for low-temperature studies

Abstract

In any laboratory to carry out temperature dependent studies a reliable temperature controller is required. Temperature controi! lers may be of analog or digital type. The main drawbacks of the analog controllers are (i) limited controllability or automation and (ii) hardware limitations in implementing mathematical computations. Digital controllers are flexible as the implementabtion of the control schemes are carried out by software only. Hence, the hardware restrictions of analog controllers can be completely eliminatec Automatic control of process parameters can be accomplished by different contrOl schemes or control algorithms such as Proportional (P), Proportional + Integral (P1), Proportinal + Differential (PD), Proportional + Integral + Differential (PID) algorithms. All the controllers produce a control output by operating on the error signal or a time series of error signals. Most process loops where the plant transfer function has not been completely defined are controlled by PID control algorithms. PID control schems can be implemented in different forms such as (i) positional or whole value form (ii) incremental or velocity form. Of the two, velocity form of PID algorithm provides certain advantages over the other. In this paper, a modified velocity form PID algorithm developed in our laboratory to control the process namely temperature is described.