Process control

The control process is a term used to indicate the whole of the materials and software being used to control and supervise the manufacturing process as products.

Composition

It generally consists of a chain of means:

physicochemical transmitters: Pressure, level, Temperature, pH, Viscosity, Turbidity, Conductivité… These sensors provide to the regulators in a continuous or discrete way the direct or indirect indication of the state of the process. Measurements can be given using converters size - analogical (for example, a level of temperature from 0 to 100 °C becomes a level from 4 to 20 my) or digitizers.
regulating: material system and/or software having in responsibility of make respect the instruction of size compared to measurements entering while providing a size of piloting to the actuators acting on the process. These regulators are generally of type pi (Proportional - Integral) or PID (Proportional - Integral - Derived).

They of predictive type, are sometimes also called also a priori (the English term used is FeedForward ). In this case, the regulators work on the basis of measurement feeding a mathematical model and/or logical more or less complex describing the behavior of the process. It is then the model which works out the size of piloting. There exist also mixed modes associating regulations traditional and predictive.

actuators: material elements acting directly on the course of the process (electro Valve, Driving, Jack…) and controlled by the regulator.

Types of process controls

The controllers of process divide themselves into two big families: " homéostats" and " servo-mécanismes".

- The homeostatic controllers aim at maintaining constant a physical or chemical size (instruction fixes) whatever the disturbances produced by the external medium on the controlled system.

- The controllers by servomechanism aim at making follow or evolve/move a physical or chemical size (variable instruction evolving/moving in time according to a dynamic diagram) whatever the disturbances produced by the external medium on the controlled system.

The diagram dynamic can be of different types:

continuous (examples): (A) assembled controlled in temperature of a liquid product, a mixture with flow and metered quantity of other solid products, followed by a controlled vacuum setting…; (b) on a copying lathe, displacement of a cutting tool whose position constantly follows that of a feeler which traverses the profile of the part to be copied, etc
batch: sequences (continuations of operations) of the process controls uninterrupted.

Random links: