Application Solution of INVT’s HMI, PLC and Frequency Inverter to Drying of PET Chips
Release Time:2015-12-25

I. Introduction

In PET production line, drying of chips is the most important step in the whole system, which determines subsequent processes directly. The drying unit adopts boiling-type pre-crystallization and rooftop-filing drying tower, and its working principle is to heat and dry PET chips and make their moisture rate be less than 30*10-6. Temperature control of hot air is the most important step in the whole technical process. If temperature for hot air is too high, chips are easy to be sticky. If temperature is too low, chips cannot be dried properly, which will deteriorate their post-processing performance. Close-loop control is adopted for the system to control air-in temperature for pre-crystallization and drying tower. Please refer to Figure 1 for its working 


Figure 1:Principle diagram for adjustment and control of pre-crystallization air-in temperature


platinum resistor PT 100 of thermometer sensor detects resistance value against the corresponding temperature, which is transformed into digital quantity via IVC1 analog quantity input module and stored in the data register. After PID operation and calculation inside the controller, 4-20mA signal is output to the actuator-pulse regulator. After the pulse regulator adjusts solid relay heating flow, it controls hot air that enters the drying tower finally .  


II. Control requirements

The set of control system is mainly made up of touch screen, PLC, analog quantity input and output module and performance requirement for screen, PLC and frequency inverter is as follows:

1.Touch screen mainly coordinates with PLC control system to monitor far-operating state of the equipment and perform the function of alarm of emergent trouble, data real-time display and modification;

2.PLC uses basic logic directives to program and control logic calculation, PID calculation to control temperature, with precision at 1℃;

3.Communication and anti-interference capability, excellent EMC and EMI property, ensuring reliability of control system and communication. 


III. Solution

1.Touch screen + PLC + frequency inverter drive program is adopted. Touch screen is mainly used to perform functions of real-time temperature display, storage, analysis and display of status parameters to fulfill real-time monitoring of control system, PLC is mainly used for status judgment and input and output control and performing communication of host computer and communication of frequency inverter.

2.CHF100A frequency inverter is chosen to guarantee precision of drive speed and start and stop speed.


IV. Advantage

1. Important data on touch screen can be displayed and modified at real time, and real-time and historical curves can be generated for search and analysis for study and reference purposes;

2.The control system can achieve free switching of manual and automatic ways and guarantee continuity of production in case of maintenance.

3.The software is of structural programming, which simplifies and clarifies programming and facilitates modification;

4.There’s an on-site control box for drying system, which enables temporary treatment in accordance with actual conditions on the spot and change far-operation way of the system. 

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