Design of Power Supply Monitoring System Based on PLC

1 Introduction
Power supply monitoring is an important monitoring system for railway signals. Before this, the power supply monitoring system of the signal basically used a single-chip microcomputer as the core of the signal acquisition system. On the one hand, the single-chip microcomputer monitoring system has technical limitations such as slow acquisition speed, unfriendly interface, and inconvenient operation. On the other hand, due to the relatively independent monitoring of the power module part, it brings many inconveniences to the power supply system, such as difficult maintenance and cumbersome interface display. Based on the above reasons, this project has developed a power supply monitoring system based on Delta PLC as the signal acquisition core and Delta HMI touch screen as the operation and monitoring interface. The monitoring subsystem and the power module are interconnected through an industrial bus network to realize an integrated, economical, practical, and technologically advanced railway signal power supply monitoring system.
2 Hardware and software system design
2.1 Hardware system design

Figure 1 Hardware system design

The design of the railway signal power supply monitoring hardware system is shown in Figure 1. System scale: 44 digital inputs; 1 digital output; 6 power modules; 39 analog inputs.
The control system is configured as follows: touch screen: DOPA75CSTD; PLC: DVP16EH00T + 1 DVP04AD-H + ​​3 DVP16HM11N; 1 power module communication card; 1 time-sharing acquisition circuit card. The
touch screen is mainly used to display acquisition data, alarm, alarm upper and lower limit settings, acquisition data display fine-tuning, alarm data display, historical trend chart display, etc. PLC is mainly used to collect data and calculate. Considering that the system does not require a very high speed for analog acquisition, in order to save costs, a DVP04AD-H is used in the system to collect 39 analog quantities in a time-sharing manner. In order to achieve this function, we have jointly developed an electronic switch circuit with the manufacturer, and divided the 39 analog quantities into ten groups, each with 4 channels, and collected them by outputting different groups. The power communication card is mainly responsible for aggregating the data of the six power modules and communicating with the PLC via the RS484 interface using the MODBUS protocol, so that the PLC can collect the data of the six power modules. To achieve this function, our company's power research and development department has done a lot of work, and finally the communication card between the PLC and the power module has achieved communication, and the information of the power module has been collected.

2.2 Software system design
(1) System function design: 44 digital quantity acquisition and display, fault judgment; 6 power module data acquisition and display, display the working status of the power module and judge the alarm; 39 analog quantity display, and judge the upper and lower limit alarm; display the alarm screen, alarm information, current alarm, alarm frequency; alarm upper and lower limit setting; data fine-tuning function, and display the fine-tuning value;
historical trend chart display; different screen opening authority setting;
It is necessary to explain the data fine-tuning function above. Since there will be errors in the measurement of the primary measuring element on site, and this error is fixed and unchanged in a short time, this part of the function is added to the program so that the final displayed value is the value after eliminating the error;
(2) The system structure design is divided into the HMI human-machine dialogue interface part and the PLC field monitoring part. The main structure of the HMI part is shown in Figure 2.

Figure 2 HMI human-machine dialogue interface

The PLC monitoring part mainly includes: power module communication; time-sharing acquisition of 40 analog quantities, 4 at a time; calculation of the acquired analog quantities according to the range to obtain the display value, display the working status of the power module and judge the alarm; fine-tuning value calculation, display value fine-tuning, and negative value elimination; faults and alarms; digital quantity acquisition and display, fault judgment;

3 Engineering
Debugging When debugging the time-sharing acquisition function, you need to pay attention to the time of time-sharing acquisition. If it is too large, it will affect the overall data acquisition time. If it is too small, it will cause confusion in the collected data. In addition, you need to add a period of time between two data acquisitions to avoid the overlap of the two sets of data. Calculate the display value of the collected analog quantity according to the range. Fine-tune the value calculation, fine-tune the display value, and eliminate negative values; note that negative values ​​may appear during fine-tuning, so consider eliminating negative values. Power module communication Note that the communication protocol during power supply communication must be set in the communication card, including the station number setting, and pay attention to the address correspondence. Faults and alarms; because there are 79 alarm points in total, it is very cumbersome and requires clear thinking.

4 Conclusion
The typical case based on the solution provided by Zhongda Telecom integrates two different types of products, reflecting the integration characteristics of a single technology platform in integrated engineering.