Key words: PLC control system

I introduction

In the production process, any control system that automatically maintains a certain proportional relationship between two or more kinds of materials is called ratio control system.  Flow control is very important in chemical industry.  This paper mainly introduces a flow ratio control system. Experiments and practice show that the system has the advantages of simple structure, small steady-state error and high control precision.

II. Working Principle

The ratio control system has three types: open loop ratio control, single closed loop ratio control and double closed loop ratio control.  Open loop ratio control is the simplest control scheme.  The single closed-loop ratio control system is designed to overcome the shortcomings of the open-loop ratio control scheme. The disadvantage of this scheme is that the residential flow does not constitute closed-loop control.  The sampling double closed loop ratio control scheme of this system.