The design of SJY-1 radio frequency monitor system based on microprocessor S3C44B0

introduction

The generator is a power system. As the capacity of a single unit continues to increase, its operational reliability is particularly important. For generators, realizing online monitoring and diagnosis after grid-connected operation has become an urgent issue to be solved. Its main purpose is to detect the defects of the generator in the initial stage, so as to arrange maintenance in a planned way, reduce the number of forced shutdowns, and avoid accidents; extend the mean time between failures and shorten the mean repair time of the generator, and reduce the generator’s cost. Maintenance fees and increase the availability of generators.

The principle of generator running status monitoring

After a long-term operation of the generator, the insulation performance gradually deteriorates, and the deterioration of the insulation structure is a comprehensive manifestation of various deteriorations. At present, the radio frequency monitoring method is a more commonly used method to monitor the insulation state of the generator.

The remote monitoring system discussed in this article cooperates with the online SJY-1 radio frequency monitor to conduct preliminary fault diagnosis by monitoring the output signal of the radio frequency instrument. How to determine the relationship between the change of the indication value of the radio frequency monitor and the change trend of the generator stator insulation is an extremely important issue in monitoring and diagnosis. According to the "fuzzy state" characteristics of the stator insulation change process of the generator, its monitoring can be divided into several areas such as good, intermediate transition, attention, warning, and danger. The insulation state of the generator is related to the signal power of the SJY-1 radio frequency instrument. Ping has a certain functional relationship.

When the detection signal of the SJY-1 radio frequency monitor is lower than 300 mV or swings near this, and the measured value has nothing to do with the generator load, the total discharge of the generator system is small, which indicates the insulation of the generator system The condition is good; when the signal level detected by the SJY-1 radio frequency monitor is higher than 1000 mV, it indicates that the discharge amount in the entire generator system is relatively large, and the maintenance personnel should pay attention to it.

However, considering that 1000 mV is not the limit for determining the internal discharge of the generator stator, it cannot be stipulated that once the RF signal reaches a certain value, it must be repaired and inspected. The time required for generator insulation to develop from an initial defect to a fault and the type of fault are different. Relatively speaking, the long-term changes of the signal can provide more abundant information for the judgment. In order to obtain the long-term change data of the signal, the monitoring system adopts the method of setting the alarm threshold and the cumulative number of alarms. First, the user sets the alarm threshold (generally it can be set to 1000 mV), and the total number of alarms is N. Then in the actual operation process, when the monitored value of the radio frequency instrument exceeds the alarm threshold, the cumulative number of alarms is increased by one, and vice versa. Only when the cumulative number of alarms is greater than or equal to N, that is, when the generator's insulation status has been in the alarm range for a long time, the monitoring system considers that the current generator may have an insulation failure, and initiates a short message alarm program to notify maintenance personnel to investigate in time.

The overall design of the system

Considering that SJY-1 RF monitor will automatically convert mV voltage (0mV~10000 mV) into mA current output (0mA~20mA), so the actual signal monitored by this monitoring system is mA current. In order to facilitate user operation, this system still uses mV voltage units when providing alarm threshold settings, and completes the conversion of numerical units during internal program processing.

The overall design block diagram of the system is shown in Figure 1. The 0mA~20mA current generated by the radio frequency instrument is converted into a voltage signal and then output to the data acquisition module, and then the microprocessor monitors the collected data. Once an abnormal situation is found, the GSM module TC35i terminal sends an alarm short message to the maintenance personnel.

Based on the microprocessor S3C44B0 to realize the design of SJY-1 radio frequency monitor system

This system uses S3C44B0X as the microprocessor. Aiming at the slower change of the current signal generated by the SJY-1 radio frequency monitor, it uses the interrupt generated by its internal timer to start the ADC at a sampling rate of 12 times per second. The data is stored in the data buffer after preliminary smoothing. When the buffer is full, dump the data to the solid state drive. If the system detects a failure, it will start the alarm program and send a short message to the maintenance personnel. Maintenance personnel can read the historical data in the solid state drive through the system and PC online, store it in the database, and analyze the cause and solution of the failure.

2.png

System hardware composition

The small system in this system with microprocessor S3C44B0X is composed of external program memory, LCD display, UART serial port, real-time clock and keyboard. On this basis, the system expands the peripheral circuits of the S3C44B0X small system, adding an ADC module, a storage module, a serial communication module and a GSM module.

The input signal of this system is a current signal of 4mA～20mA generated by a radio frequency instrument, which is converted into a voltage of 0V～4V after precision resistance and input to the 4-channel, 12-bit, parallel/serial ADC chip ADS7824. In the design, channel 0 was selected as the input of the original signal, and the remaining three signals were reserved for future development. At the same time, the serial working mode is selected. The circuit of ADC module is shown as in Fig. 2. In order to ensure that the circuit board is a single power supply, a DC-DC converter is used in the ADC module of this design to provide the dual power supply required by the isolation amplifier.

Considering that the system needs large-capacity data storage, the storage chip is small in size and low in power consumption, so Samsung's NAND structure Flash storage device-16MB K9F2808 is selected as the solid-state hard drive of this system. Its power supply voltage is 2.7V~3.6V, read and write by page, and erase by block.

In addition, the system also requires its GSM module to support short message service, with a standard RS-232 interface and SIM card interface, and can be directly interfaced with AT commands. Therefore, the Siemens TC35i terminal with built-in TC35i wireless module is used as the GSM module of the system, and it communicates with it through the full-function serial port UART1.

System software design

System software design includes lower computer software design and PC software design. The former is mainly composed of a human-computer interaction module, a data acquisition and storage module, and a short message sending module (the process is shown in Figure 3), while the latter includes two parts: a serial port communication module, a main interface, and a database design.

The human-computer interaction module is composed of an LCD display and a keyboard, and is responsible for setting the parameters of the system, such as alarm thresholds, alarm counting thresholds, SMS service center numbers and maintenance personnel mobile phone numbers, etc. As mentioned earlier, this system uses mV voltage when providing alarm threshold settings, and completes the conversion of numerical units through internal procedures. In addition, considering that the maintenance personnel need to import the data in the solid-state hard drive into the PC, the software design also specifically sets the PC data transfer function. When the specified key interrupt is generated, the software will automatically shield other interrupts and start the data dump subroutine, thereby reading the data in the solid-state hard disk by page and sending it to the PC through the serial port.

The data acquisition and storage module is mainly responsible for sampling and reading and writing of hard disk K9F2808. The sampling frequency is 12 times per second, which is started by the MCU internal timer interrupt.

The short message sending module is mainly responsible for the user data area coding and the sending of alarm short messages. In this design, the communication rate between the MCU and the TC35i terminal is set to 19200bps, and the AT command set is used for communication. The AT command is a character-based command structure, with TEXT mode and PDU mode, as well as the BLOCK mode used in the early days. Among them, the PDU mode is commonly used in GSM mobile devices. This model is also used in this design.

In the PC software design, the serial port communication module is responsible for the sending and receiving of data between the PC and the lower computer, and the design of the main interface and database is to better realize the remote monitoring function of the system.

Conclusion

This design realizes the remote monitoring system based on S3C44B0X. Experiments show that the system has good real-time performance, reliable performance and strong practicability. In addition, because the short message service has the advantages of always online, no dialing, low price, and wide coverage, the system is especially suitable for some applications with small communication data volume.