1. Introduction

The whole set of equipment is divided into 3 sets of circulation systems, namely Chilled circulating water system, Heat exchanger cooling water circulation system, and Water cooling unit cooling water circulation system. The main equipment includes 1 deionized water tank, 2 chilled water circulation pumps, 1 plate heat exchanger, and 1 water cooling unit, of which the chilled water circulation pump operates by frequency conversion speed regulation.

2. Process Requirements

1) Process Flow

Water tank → Chilled water circulating pump → Plate heat exchanger → Water cooling unit → Chilled water equipment for hall → Water tank

2) Control Principle

The chilled water circulating pump and water cooling unit in the chilled water supply and circulation system is running automatically. The circulating pump is controlled by pressure, operates with variable frequency, and the operating pressure is  0.4MPa; the electric regulating valve 1 is controlled by the temperature T2 of Circulating chilled water from the Outflow plate heat exchanger. when T2 reaches 19.5°C (editable), the electric regulating valve 1 is opened up, to increase the Circulating chilled water from the Outflow plate heat exchanger to reduce T2; when T2 reaches 17.5°C (editable), the electric regulating valve 1 is closed down, to decrease the Circulating chilled water from Outflow plate heat exchanger to improve T2. The water cooling unit is controlled to start and stop by the chilled water temperature T4 after the mixing of the circulating chilled water from the Outflow water cooling unit and the bypass circulating chilled water. When T4 of the circulating chilled water reaches 20°C (editable), the system will start the circulating cooling The water electric valve will start the water cooling unit for cooling after 1 minute. When the temperature T4 of the circulating chilled water reaches 17°C (editable), the system will stop Water cooling unit and close the electric valve after 3 minutes.

3. Solution Analysis

The control system using PI3102i, PLC is LX3V_2416MR-A, modules LX3V-4AD and LX3V-4DA.

Reason for selection: Low cost and multi-analog control, 3V has similar module applications before, and the program compatibility can reach 7 AD modules and up to 28 analog processing operations, which is convenient for program debugging.

Main Control Principle:

1. Constant pressure mode: This set of systems started as a one-for-use and one-for-preparation purpose in the installation instructions document. But it was found in the field test that the pressure is not able to reach the requirements, so it was changed to a pump control mode with one-for-use and one-for-supplement.
2. Manual mode: Carefully research the customer's wiring circuit diagram, although the manual power frequency is directly realized by the hard wire, but the manual operation in the PLC still needs the control of each device, which has met the control needs of on-site debugging.
3. Module monitoring: There are many analog quantities in this project, and a separate module debugging screen is required to facilitate the debugging of analog quantities.
4. Automatic mode: Automatic operation according to the process, data recording, alarm recording and other functions.

4. Program Introduction  

HMI Program:

Figure 1 Monitoring screen of the rectification system

Figure 2 shows the manual screen for debugging

Figure 3 is the analog debugging screen

Figure 4 is the analog processing subroutine

Figure 5. The calculation of each channel is carried out according to the module, which can be programmed in modules to save time.

Figure 6 is the control program of one-for-use and one-for-supplement in the automatic program, which is the control core of this program

5. Project Summary

This debugging summarizes the following points

1. According to the technical requirements, sometimes it needs to be able to meet the on-site working situations, and it needs to be improved according to the actual situation. Like this time, the model of the pump is changed from one-for-use and one-for-preparation to one-for-use and one-for-supplement.
2. The processing of the analog quantity is programmed by the previous molding procedure to improve the programming efficiency.
3. The customer began to use communication for data exchange with the compressor unit, but in the later stage, due to the epidemic equipment technology was not able to reach the site, the later stage used hard wire for data exchange to achieve the same effect.