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Optical fiber radio frequency transmission is a technology
Optical fiber radio frequency transmission is a technology that transmits radio frequency signals through optical fibers. Its structural principles mainly include the following aspects:
1. Basic principle of optical fiber transmission: An optical fiber is composed of a fiber core and a layer of cladding. The core of the optical fiber is made of high refractive index material, while the cladding is made of low refractive index material. Through this The structure can realize the total internal reflection of Industrial Router/Gateway light, so that the light is transmitted along the fiber core. The transmission characteristics of optical fiber include high bandwidth, long transmission distance, and small signal attenuation.
2. Radio frequency optical modulator: A radio frequency optical modulator is a device that converts radio frequency signals into optical signals. It can modulate radio frequency signals by changing the intensity, frequency or phase of optical signals, thereby converting radio frequency signals into optical signals.
3. Optical fiber transceiver: Optical fiber transceiver is a device that converts optical signals into electrical signals or converts electrical signals into optical signals. In the process of optical fiber transmission, it is necessary to convert optical signals into electrical signals for processing or convert electrical signals into optical signals for transmission. Optical fiber transceivers usually include components such as optical-to-electrical converters, amplifiers, and filters.
4. Fiber optic coupler: A fiber optic coupler is a device that connects multiple optical fibers together. It can realize the mixing and separation of multiple signals, and transmit multiple radio frequency signals through optical fibers. ethernet to rs485 converter To sum up, the structural principle of fiber optic radio frequency transmission is to transmit radio frequency signals through optical fibers, in which radio frequency optical modulators and optical fiber transceivers are key devices to realize the mutual conversion between optical signals and radio frequency signals, and fiber optic couplers can realize multiple signal transmission. mixing and separation.
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The device adopts NS1-TB and configures the parameters
Modbus Gateway - Simple Protocol Conversion
In the previous article, we have introduced several main types of Modbus gateways in detail. Today, let us introduce the process of simple protocol conversion among them.
Simple protocol conversion is the most conventional and common Modbus gateway function, and it is also the Modbus gateway mode with the highest data processing efficiency. It only extracts the key fields in the data, and then encodes the extracted data with another protocol (Modbus RTUM, Modbus TCP) and sends it .
Demo Request & Data Analysis
In order to display the Modbus data frame correctly and visually, use the standard Modbus debugging tool to test. Modbus Poll and Modbus Slave are not free software, but they can be used for free for 30 days. If you need to use them for a long time, please purchase genuine ones.
The device adopts NS1-TB and configures the parameters as shown in the figure below:
Open the Modbus Poll software, click Connection to connect to the serial port server and configure the communication protocol, as shown in the figure below:
Turn off automatic reading, which is convenient for analyzing data frames. If you configure the host request first, it will cause the device request to time out. Don’t worry about it. After the slave simulation is completed, there will be no response timeout.
ModBus RTU protocol and ModBus TCP protocol
Open Modbus Slave, click Connection to connect to the serial port server and configure the communication protocol. The master has already used the network connection, and the slave needs to use the serial port connection, as shown in the figure below:
Open the data monitoring serial port, the method of Poll and Slave is the same as shown in the figure:
Click to read a register, 10 registers cannot be directly displayed in the debug window, reducing the number of read registers;
Configure the number of reads:
It can be seen from the figure below that the "simple protocol conversion" of the serial port server caches the message identifier "00 0D" of the received TCP data frame, adds Modbus CRC check to 01 03 00 00 00 02, and then outputs the data frame from the serial port. The slave machine receives the command and returns the Modbus RTU response data frame, and the serial server calculates the frame length after receiving the data, and then encodes the cached message identifier and frame length into the data frame and sends it through the network port.
Although "simple protocol conversion" has high processing efficiency, it cannot handle multi-host requests, so there are "multi-host mode and storage gateway". We will introduce the multi-host mode and storage gateway working mode in detail next time.
After understanding the principle of virtual short and virtual break,
After understanding the principle of virtual short and virtual break, we can use it to judge whether the device is good or bad in the actual application of the operational amplifier circuit. According to the principle of the virtual short of the amplifier, if the op amp works linearly, the voltages at the same input terminal and the reverse input terminal must be equal, even if there is a difference, it is at the mv level. Of course, NB-IOT wireless communication in some high input impedance circuits, the internal resistance of the multimeter will have a little influence on the voltage test, but generally it will not exceed 0.2V. If there is a difference of more than 0.5V, the amplifier must be damaged!
In many instruments and meters, there are integrated operational amplifiers for small signal amplification. It is more fragile than other integrated blocks and components, so it can be said to be a shortcut for repairing instruments and meters to quickly judge whether it is good or not. Many integrated blocks in more complicated instruments are directly welded on the printed circuit board, the circuit board is inserted into the socket, and the distance between the circuit boards is also very small, so it is difficult to directly measure the voltage. Some simple and practical methods for judging integrated op amp blocks are proposed below.
1. After powering on for a period of time, touch the temperature of the integrated op-amp block by hand. If the temperature is greater than 50°C, you should suspect whether it is damaged.
2. If possible, measure its DC current and it should be within a few milliamperes. Otherwise it is damaged.
3. The integrated op amp has a single op amp and several op amps combined, and you should be familiar with its power supply and input and output pins. There are also certain rules that can be found and found in relevant manuals. The resistance between the input pins of the integrated operational amplifier should be relatively large (generally greater than 10 M ohms). If the measured value is small, it should be observed that there is a diode with infinite value at the input end, otherwise it will be damaged.
4. The online measurement input voltage should be relatively small. Generally below 0.1 V. If you touch the input terminal with your hand, the voltage should change at the output terminal, or if you touch the two terminals of the feedback resistor with your hand (equivalent to connecting a resistor in parallel), the output will also change accordingly.
4G wireless smart meter reading, more than a little easier!
4G wireless smart meter reading, more than a little easier!
With the development of the Internet of Things, people's lifestyles are changing subtly, and work and life are gradually shifting from traditional offline to online. More and more companies are also adopting offline and online management models to improve LoRa technology business Viability and competitiveness, meter reading is no exception.
In daily property management, meter reading is a tedious task, and the traditional meter reading mode has many disadvantages:
1. Manual meter reading is troublesome and error-prone
2. Dispersion distance is long and time-consuming
3. The efficiency is too low and the labor cost is too high
Aiming at the defects of the traditional meter reading method, the 4G wireless smart meter reading system came into being. Based on the 4G communication technology of the three major operators, it has the advantages of fast transmission speed, low communication cost, convenient installation and low cost, no need for additional wiring, and stability. Strong, not limited by distance and many other advantages, the use of 4G wireless meter reading solution can effectively reduce labor costs and improve the accuracy of data statistics.
Ebyte EC04 module is perfectly suitable for 4G wireless smart meter reading system. This module has the following advantages:
1. Not subject to regional restrictions: adopt CAT1 solution, support 4G full Netcom, wide coverage, high stability, low delay, and can be applied to various environments, such as mountainous areas, towns and other areas with underdeveloped traffic;
2. Support multiple working modes: network transparent transmission (TCP/UDP), MQTT mode, HTTP mode, SMS transparent transmission, customers can choose the desired transmission mode;
3. Support quick access to Alibaba Cloud, Baidu Cloud, onenet and version 3.1 standard MQTT servers, and can quickly access the MQTT servers built by customers to realize data uploading to the cloud;
4. Support multi-link edge acquisition, support modbus automatic CRC check, and can automatically convert the collected modbus data into modbus tcp;
5. The module is small in size, easy to install and convenient for wiring.
Thanks to these features, the EC04 module connected to the meter can transmit data to the server through the 4G network. After configuration, it can be used after power-on, and the operation is convenient. This can save the cost of arranging communication lines and save Labor costs.
The 4G networks of the three major operators cover the whole country, so the EC04 module can receive meter reading data from various places without distance restrictions, and realize the effect of centralized management of multi-place meters by one server. If customers have control needs, the EC04 module can also Realize remote control of the meter, no matter which region or city the meter is installed in, as long as there is a signal at the location of the meter, remote control can be realized, such as the timing switch of the meter according to customer needs.
Ethernet - the composition and working principle of the network card
A Network Interface Card (NIC for short), also known as a network adapter, is a device that connects a computer to a local area network. As long as it is connected to a LAN, a network card needs to be installed. wireless communication A network card mainly includes the bottom two layers of OSI, the physical layer and the data link layer. The chip of the physical layer is called the PHY, and the chip of the data link layer is called the MAC controller. After an introduction (Ethernet - PHY, MAC and MII basics).
The network card works in the last two layers of OSI: the physical layer and the data link layer. The physical layer defines the electrical and optical signals, line status, clock reference, data encoding and circuits required for data transmission and reception, and communicates to the data link Layer devices provide standard interfaces. The data link layer provides functions such as addressing mechanism, data frame construction, data error checking, transmission control, and standard data interface to the network layer. The chip of the data link layer in the Ethernet card is called the MAC controller. These two parts of many network cards are done together. The relationship between them is that the PCI bus is connected to the MAC bus, the MAC is connected to the PHY, and the PHY is connected to the network cable (through the transformer).
Connect MAC and PHY through the standard MII interface defined by IEEE. This interface is defined by IEEE. The MII interface transfers all data and data control of the network. The MAC determines the working state of the PHY and controls the PHY by using the SMI (Serial Management Interface) interface by reading and writing the registers of the PHY. Part of the registers in the PHY are also defined by IEEE, so that the PHY reflects its current status into the registers, and the MAC continuously reads the status register of the PHY through the SMI bus to know the current status of the PHY, such as connection speed and duplex capability wait. Of course, you can also set the PHY registers through SMI to achieve control purposes, such as opening and closing flow control, auto-negotiation mode or mandatory mode, etc.
Therefore, whether it is the physically connected MII interface and SMI bus or the status register and control register of the PHY, there are IEEE specifications, so MACs and PHYs of different companies can work in harmony. Of course, in order to cooperate with some unique functions of PHYs of different companies, the driver needs to be modified accordingly.
When the PHY sends data, it receives the data from the MAC (for the PHY, there is no concept of a frame, for it, it is all data regardless of the address, the data is still CRC), and every 4 bits add 1 bit of error detection Code, and then convert the parallel data into serial stream data, and then according to the coding rules of the physical layer (NRZ coding of 10Based-T or Manchester coding of 100based-T), the data coding is converted into an analog signal and sent out. The process of receiving data is reversed.
When a CMOS process chip is working, the signal level generated is always greater than 0V (this depends on the process and design requirements of the chip), but such a signal will have a large DC voltage when it is sent 100 meters or even farther away. weight loss. Moreover, if the external network cable is directly connected to the chip, electromagnetic induction and static electricity can easily cause damage to the chip.
Furthermore, the grounding method of the equipment is different, and the different grid environment will cause the 0V levels of the two parties to be inconsistent. In this way, the signal is transmitted from A to B. Since the 0V level of A equipment is different from the 0V level of B point, this will cause a large current. Flow from a device with a higher potential to a device with a lower potential. At this time, Transformer (isolation transformer) is needed. It filters the differential signal sent by the PHY with a differential-mode coupled coil coupling filter to enhance the signal, and couples it to the other end of the network cable through the conversion of the electromagnetic field. In this way, there is no physical connection between the network cable and the PHY and the signal is transferred, the DC component in the signal is cut off, and data can also be transmitted in devices with different 0V levels.
The isolation transformer itself is designed to withstand the voltage of 2KV~3KV, and at the same time it plays the role of lightning protection. Some users' network equipment is easy to be burned out in thunderstorm weather, most of which are caused by unreasonable PCB design, and most of them burnt the interface of the equipment, and few chips are burned, because the isolation transformer plays a protective role.
When sending data, the network card first listens to whether there is a carrier on the medium (the carrier is indicated by the voltage), WLAN communication technology and if there is, it thinks that other stations are transmitting information and continues to listen to the medium. Once the communication medium is quiet for a certain period of time (called the inter-frame gap IFG=9.6 microseconds), that is, it is not occupied by other stations, frame data transmission is started while continuing to listen to the communication medium to detect collisions. During the transmission of data, if a collision is detected, the transmission is stopped immediately, and a "block" signal is sent to the medium to inform other stations that a collision has occurred, thus discarding the corrupted frame data that may have been received, and waiting A random amount of time (CSMA/CD's algorithm for determining the waiting time is a binary exponential backoff algorithm). Wait for a random amount of time before making a new send. If a collision still occurs after multiple retransmissions (greater than 16 times), the transmission is abandoned.
When receiving, the network card scans each frame transmitted on the medium, and if it is less than 64 bytes in length, it is considered a collision fragment. If the received frame is not a conflicting fragment and the destination address is a local address, check the integrity of the frame, if the frame length is greater than 1518 bytes (called an oversized frame, it may be caused by a wrong LAN driver or interference) or If it fails to pass the CRC check, it is considered that the frame is distorted. Frames that pass the verification are considered valid, and the network card receives them for local processing.