The prospect of replacing mechanical and/or electromechanical
components by electronic circuits promised to enhance significantly the speed
and storage capacity of machines. A computing instrument designated the ENIAC (Electronic
Numerical Integrator and Calculator) is generally regarded to be the first
electronic computer.
The ancestry of both electronic analog and digital computers can be
traced to mechanical devices, the first of which appeared in the seventeenth
century. During the 1630s, W. Schickard developed a somewhat unreliable mechanical
calculator in Tuningen, Germany. The first mechanical analog unit is perhaps the planimeter, a device
developed by J.H. Herman about the year 1814, and used to evaluate the area
bounded by a contour.
Early Process Computing.While there was nothing like today's digital
process control computer in the late 1930s and early 1940s, process control
systems began to do sоmе modest computing. Instrument engineers started to tie a number of
control elements together to perform computations, and began to take into account
multivariable control.
The complexity of the present-day automation in a process plant can be
characterized by the large number of recording controllers interconnected by
the flow diagram on the centralized control panel board in a process control
room. On the control board, the process is divided into several interconnected
unit operations, such as reactor, heat exchanger, etc.
The instrumentation industry emerged during the
industrial revolution, with some companies being formed in the mid-18ООs. These companies developed sensors and measurement and control
devices.
Generally speaking,
process control is the ability to control multiple variables such as temperature, pressure,
flow and level to obtain the desired results from a process. Consider a mixing
tank into which two products of different temperatures are flowing.We want to maintain
the temperature in the tank at a certain value. We insert a temperature sensor
such as a thermocouple into the tank.This sensor sends to a control instrument a small
electrical signal proportional to the actual temperature.The controller compares
the actual temperature with the desired or set-point temperature and sends out
a control signal to one or both valves controlling product flow into the tank.
