Digital control of industrial processes has become very important today because of the advantages it offers and the increased availability of inexpensive computing power of microprocessors. The principal advantages include fixed hardware with complete software flexibility and the feasibility of implementing integration and differentiation on extremely slow varying signals. On the other hand digital controllers have some drawbacks also such as errors due to the processes of sampling and reconstruction, computational errors caused by finite wordlength, truncation, register overflow, as well as the de-stabilisation effects of sampling. A clear understanding of all these aspects is of great value to a student of control engineering.
In the present unit a second order transfer function, simulated with operational amplifiers and passive components, has been chosen as the process to be controlled. This results in a well behaved and near perfect linear process which gives a highly predictable performance and enables the student to concentrate on the design and evaluation of the controller. The digital controller consists of a 8085 based microprocessor kit with analog-to-digital and digital-to-analog interface. The dynamic ranges of the variables in the whole system and that of the built-in square wave test input signal are made compatible. The step response may be displayed and studied using an external measuring CRO.
Software supplied with the system resides in a 8K EPROM. This consists of P, P-I and P-I-D algorithms in which the three gains may be selected out of 16 levels each.
All arithmetic calculations are performed in 16-bits and are also available to the user as subroutines. Detailed information and listing of the software is included in the literature, besides suggestions and procedures for conducting experiments. Also included are typical results of some experiments with their theoretical descriptions. Further, the user may write his own programs to implement additional algorithms and study their responses.
Identification of the controlled process
Study of sampling period variation
Designing P, PI, PD and PID controllers
Advanced algorithms implementation
Features & Specifications
Second order simulated process (analog process)
Built-in D/A and A/D circuits (8-bit)
8085 based mP kit as digital controller with user software in 8K EPROM
16-bit arithmetic for algorithmic calculations
IC regulated internal built-in power supplies
16 built-in levels of P, I and D gains each. Complete flexibility for the user to develop own software
Square wave test input (internal)
220V±10%, 50Hz mains operation
Detailed literature and patch cords included
Essential accessory – a CRO