Wireless meter reading solution that adapts to multiple smart meter communication protocols

    Abstract: This article describes a wireless data transmission module that adapts to a variety of smart meter communication protocols and can be embedded in multi-function meters and power negative control devices to complete remote wireless meter reading and remote control solutions. The radio frequency module adopts FC-210/E from Shenzhen Youxunda Communication Equipment Co., Ltd. This module adopts narrow-band frequency modulation method, and the data modulation adopts FFSK (MSK). The two-way data transmission is reliable and the bit error rate is low, effectively ensuring the data transmission of smart meters such as electric energy meters. It can be widely used in remote meter reading and other intelligent meter centralized reading fields.

    Keywords: remote wireless meter reading, wireless data transmission module, energy meter communication protocol

Wireless meter reading has long been popular in developed countries and regions. The meter reading vehicle walks near the user's meter, and various data from the meter are copied into the computer of the meter reading vehicle. However, wireless meter reading has just started in China, and the communication protocols for data transmission during the collective reading process are also diverse. Although the Ministry of Electric Power released its industry standard - Multifunctional Electrical Energy Protocol in 1998,However, due to various historical reasons, universalization is an ideal until now. How to better realize the inclusiveness, openness and transparency of wireless data transmission is what application personnel and manufacturers are most concerned about.

This article introduces a data transmission system that can accommodate multiple communication protocols. It is an embedded wireless meter reading solution that conforms to the actual situation of remote wireless data transmission in my country's electric power industry. It has been successfully used in many electric meter factories and achieved good social benefits.

1 Introduction to my country’s electric energy meter data communication protocol

Basically, many electric energy meter communication protocols running in our country are derived from the VAN_COMM protocol. The VAN_COMM protocol is an information transformation standard developed by the American FERRANTI company. It is suitable for "master-slave" or "question-and-answer" processing environments. The master station (usually one) actively asks the substations (multiple), and the substations only passively answer. The following are two representative communication protocols in my country.

1.1 Multifunctional electric energy meter communication protocol (national electric power industry standard)

The protocol is a master-slave structure half-duplex communication method. The handheld unit or other data terminal is the master station, and the rate device is the slave station. Each rate device has its own address code. The establishment and dismantling of the communication network are controlled by the information frames sent by the master station. Each frame consists of 7 fields including frame start character, slave address field, control code, data length, data field, frame information longitudinal check and frame end character. Each part is composed of several bytes.

a. Byte format: using RS-232 protocol

Each byte contains an 8-bit binary code. During transmission, a start bit (0), an even parity bit and a stop bit (1) are added, for a total of 11 bits. The transmission sequence is as follows: b.

    Frame format as follows:

Among them: L≤200

1.2 "Hunan" Communication Protocol

"Hunan" communication protocol refers to the communication protocol of Hunan Wasion Electric Meter Factory. The main features of this protocol are as follows:

Communication interface: standard asynchronous RS-232/RS-485

Word format: 1 start bit, 8 start bits, even parity, one stop bit;

Baud rate: 300bps/600bps/1200bps/4800bps, default 1200bps;

Frame format:

Among them: L≤255

The two protocols introduced above are the most representative communication protocols for domestic electric energy meters. From the above regulations, the following common points can be summarized:

·The communication interface is RS-232/RS-485 interface;

·Frame length: ≤256byte;

·Baud rate: variable from 300 to 9600bps;

·Two-way half-duplex communication method;

·The frame length is undefined.

2 FC-201/E wireless meter reading solution

2.1 Working principle of FC-201/E wireless data transmission module

FC-201/wireless data transmission module is a small two-way data transmission radio station with a modular structure. It has a built-in high-performance microcontroller, signal modem, VHF/UHF band radio frequency module and RS-232 standard communication interface. The data input from the RS-232 interface is modulated by FFSK (MSK), and then transmitted after frequency modulation by the radio frequency module; after the receiving radio frequency module receives the radio frequency signal, it is restored to data after digital signal processing by the receiver, and is sent back to the user system to This completes the two-way wireless transmission of data between the two users. The principle is shown in Figure 1.

The data sending and receiving process is as follows:

(1) Data transmission is shown in Figure 2.

(2) Data reception is shown in Figure 3.

2.2 FC-201/E wireless meter reading solution

The basic design idea of ​​the FC-201/E wireless meter reading solution is to use a wireless method to implement a centralized reading center or handheld meter to monitor various meters while keeping the existing various multi-function meters basically unchanged. of wireless data sets. System composition of FC-201/E wireless meter reading solution.

Here's how it works:

The centralized metering center (handheld reader or integrated meter) queries and calls each meter according to the communication protocol of each meter. The address allocation and definition of each meter are determined by the protocol of the multi-function meter. The content and process of collective copying in the collective copying center can be downloaded through the upper-level software. When the centralized reading center wants to obtain the data of a certain multi-function electric meter, the data with the address code of the meter will be transmitted to FC-201/E in the form of RS-232. The FC-201/E of the central station will receive the RS- 232 information, it is converted into a wireless signal and sent out. The wireless multi-function meters in peripheral stations are in the receiving state (i.e., listen) under normal conditions. After receiving their own address information, they execute the instructions of the centralized reading center and send the data required by the center to the center.

2.3 Key technical points of implementing wireless meter reading system using FC-201/E

Using FC-201/E to implement wireless meter reading must solve the following problems:

(1) Reliability of data transmission

Since the installation environment of multi-function meters is uneven and the electromagnetic environment is also the same, FC-201/E adopts the following measures to achieve reliable transmission of wireless data:

·Adopt narrowband communication solution

The communication bandwidth is 25kHz, and the out-of-band suppression ratio of reception and transmission is ≥60dB, which greatly reduces the probability of interference signals falling into the band.

·Using frequency modulation communication system

FC-201/E adopts frequency modulation communication system. During the communication process, the characteristics of the baseband signal are reflected in the field characteristics of the wireless signal during the wireless transmission process. Therefore, during the transmission process, the signal characteristics of the receiving point will not change due to changes in the signal strength of the receiving point, which greatly improves the anti-multipath capability and can also adapt to a variety of installation environments.

·Adopted error correction and error detection measures

(2) Inclusiveness of data protocol

As can be seen from the previous introduction, the communication protocols of multi-function meters in my country are the same, but the specific contents have their own characteristics. In the previous design process, most manufacturers relied on wired or infrared communication methods as wireless data transmission. To achieve reliable transmission of data, it should be transmitted in a frame structure. However, it is difficult to meet the requirements using traditional fixed frame transmission. In order to improve the inclusiveness of data transmission, the following inclusive design solutions are adopted in the design of FC-201/E:

·Dynamic framing of air data;

·Interface rate adaptation;

·User data is fully transparent.

The FC-201/E designed in this way has completely abandoned the connotation of various energy meter communication protocols, and realized fully transparent transmission of various communication protocols between the meter and the collector.

(3) Timeliness of data transmission

In the FC-201/E wireless meter reading solution, the timeliness of data transmission is a very critical parameter, which is directly related to the capacity of the system. In order to improve the timeliness of FC-201/E data transmission, the FFSK (MSK) modulation method is first used in the modulation method, thereby supporting a transmission rate of 2400bps. At the same time, the transmitter's fast start technology is used in the hardware to ensure The transmitter's turn-on time is ≤25ms.

The receiving sensitivity of FC-201/E is as high as 0.25 μV and the transmitting power is 50~100mW, which can achieve an effective distance transmission of 500~800m. The volume of FC-201/E is 46mm×72mm×14mm, so it can be easily embedded into an electric meter.

FC-201/E can adapt to a variety of communication protocols. Various smart meters only need to connect their RS-232/RS-485 or UART with the communication interface of FC-201/E to easily realize centralized wireless meter reading. .

With the rapid development of modern computer technology and wireless communication technology, it has become an inevitable trend to fully realize the modernization of power management and centralized meter reading. Especially when power line carrier meter reading, IC card prepaid meters and infrared meter reading encounter many problems in practice, we firmly believe that FC-201/E will create a new situation for wireless remote meter reading.