Abstract：This paper introduces the application of UniMAT PLC in pH value online detection and control system. In the process of printing and dyeing, the monitoring of PH value is an important link. The environment of printing and dyeing enterprises is special. There are two difficult problems in the testing of PH value: how to improve the reliability and accuracy. The PH value of mercerizing machine cloth surface is one of the most important factors affecting color difference in pretreatment. The PH value of finished cloth has strict standards. The PH value must be controlled within a reasonable range. The introduction of UniMAT PLC into the on-line detection and control system of PH value as its automatic control core effectively realizes the on-line detection and fault diagnosis of PH value, achieves the purpose of fault-tolerant testing, realizes the transformation of PH value from manual measurement to quantitative control, improves the testing accuracy of PH value, and meets the requirements of high-grade products.

Key words: pH online detection, UniMAT PLC, automatic control, PID

1. Introduction

Most of the domestic printing and dyeing wastewater PH value control is basically completed by manual operation, its shortcomings: measurement value is not easy to grasp, poor real-time, poor reproducibility of production process, so many factors restrict the further improvement of product quality. Therefore, it is particularly important to develop a pH online control system. PH value on-line detection and control system is a new technology which sprang up in the 1980s and is widely used in all walks of life of construction machinery. In recent years, China has accelerated the development and innovation of PH value on-line detection and control system. Perfect monitoring system, stable operation and precise PID control characteristics have become the key points of excellent printing and dyeing PH treatment equipment.

2.working principle

The system consists of UniMAT PLC, detection electrode, PH value control instrument, frequency converter, metering pump, control box, touch screen and other parts. According to PH probe detected PH value, output detection signal to the control instrument and PLC, touch screen display actual PH value, PLC use PID control, according to the set PH value control speed of the feeding speed pump, automatically add acid to the pool to neutralize alkali, so that sewage to reach the set pH value. The whole system is precise, stable and reliable. It adopts PLC intelligent design and has powerful functions, such as automatic zero stabilization, digital display, over-limit alarm, transducer output, current regulation output or time proportional output, RS485 communication and so on. The working principle is shown below

：

3.system composition

The system consists of detection electrode, PH value control instrument, frequency converter, metering pump, control box, UniMAT PLC, touch screen and other parts. The electronic control system consists of UniMAT PLC system, HMI system, low-voltage electrical apparatus, sensors and actuators. The configuration of UniMAT PLC system is shown in table 1

.

                         Table 1: configuration of Yiwei PLC system

Comparing with the similar products on the market, Yiwei CPU 124XP-2R has the following excellent characteristics: CPU itself comes with 10DI/8DO, 4AI/2AO, DC 24V power supply. Four channels of AI and two channels of AO are added. The system saves an analog input module and an analog output module for customers because of the need for an analog input and an analog output module. Additional PPI ports have been added to save customers from the trouble of using touch screens and programmed cable ports at the same time, which can only be plugged in and out of ports continuously; no batteries are needed to provide more than 10 years of power-down data to maintain; faster instruction execution speed, a single Boolean operation instruction is three times that of similar Siemens products. The appearance of CPU 124XP-2R products is shown in figure 2...

                                  图2 亿维 CPU124XP-2R产品外观

4.control process

The electric control system of PH value on-line detection and control system is PLC control system, the core is composed of upper computer and lower computer. The subordinate computer is billionaire CPU124XP-2R PLC, and the upper computer is LCD touch screen or HMI. The user interface is friendly and easy to operate. The device monitors the PH value in all directions; the LCD touch screen can display all kinds of setting parameters and running state of the system; the user can change the local mode, remote mode, test mode, etc. of the system; the user can also modify the PH value according to the actual needs to ensure that the sewage discharged can meet the discharge requirements; when there is a failure, the system may be. Display the location of the fault and alarm, in addition to password protection function also requires the user to change the system settings parameters to confirm identity, to ensure that the system is not random operation. The control process diagram is shown in figure 3..

ig. 3 control technology

Main technical parameters:

1). PH measurement range: 0pH - 14pH;

Display resolution: 0.01pH;

(3) pH control accuracy: + 0.3pH;

The suitable environment for sensors is less than 80 degrees Celsius.

Working environment:

Power supply: three phase AC 380V + 10% 50Hz + 2%<1.5KVA;

2). Ambient temperature: 0~50 C;

3). Ambient humidity: no more than 95%RH (no condensation).

4).Altitude: not more than 1000m;

5).Working mode: continuous.

5 system effectiveness

The protection effect and economic benefit of the PH value on-line control system are obvious. The main effects are as follows:

(1) change the traditional transformation from the operator's titration pH value to the system intelligence measurement.

(2) To reduce the randomness of titration, the whole process of measuring the PH value of the system is completely realized by the process room.

(3) improve product quality and success rate.

(4) reduce the problem of dyeing, cylinder difference and batches.

(5) shorten dyeing time and increase output.

(6) the dyeing and dyeing rate is increased, and the dye is saved. The color stability and color fastness are high, and the quality is ensured.

(7) environmental protection and energy saving.

6 concluding remarks

The application of UniMAT PLC in the PH value on-line control system shows the high compatibility with Siemens PLC and the excellent characteristics of stable performance. UniMAT PLC can completely replace Siemens products, ensuring the stability of the product while reducing the manufacturer's production costs.