Do you know what a "POE switch" is?

Nowadays, in the large and medium-sized security monitoring places, almost all of the WiFi coverage is installed, and the webcam is installed. Many engineers are already using PoE switches, but what exactly is a PoE switch? Xiaobian today will explain the rigorous PoE switch knowledge. .
PoE&PoE switch
POE (Power Over Ethernet) refers to some IP-based terminals (such as IP machines, WLAN access point APs, network cameras, etc.) without any changes to the existing Ethernet Cat.5 cabling infrastructure. A technology that can also power these types of devices while transmitting data signals.
A POE switch is a switch that supports network cable power. In addition to the data transmission function of a common switch, it can also supply power to the network terminal. In other words, the role of the PoE switch is mainly data transmission and power supply.
Common PoE switch ports
POE switches generally have 5 ports, 8 ports, 9 ports, 16 ports, 24 ports, and 48 ports. You can select the number of POE switches based on the number of devices you need to access and the application scenarios.
Advantages Disadvantages
advantage:
The wiring is simple, no need to repeatedly arrange the data transmission line and the power supply line, and the network cable can be extended up to 250 meters, which can meet the requirements of long-distance security monitoring power supply transmission, improve data forwarding efficiency, save time and space.
With powerful data processing capabilities, security monitoring has high requirements on the throughput and latency of the switch, which can meet the smoothness and stability of video transmission of multiple HD cameras.
Disadvantages:
The cost is higher, because the PSE chip is used, and has strong data processing capability, so it is more expensive than the ordinary switch; but overall, including wiring, management, etc., the overall cost is actually more cost-effective.
E.g:
A company wants to arrange network monitoring. There is no power socket in the corridor, corner, etc., and you want to manage these cameras in a unified way. Then you can use one or more PoE switches to solve it. You don't have to go to the wiring and power outlets. It is also easy to manage.
IEEE802.3af&IEEE802.3at
The power supply standards for POE switches mainly cover two types:
First, IEEE802.3af, EEE 802.3af standard is to achieve Ethernet equipment power supply through Ethernet data line pair or backup line pair, thus getting rid of the trouble brought by the use of AC adapter, and will further expand the application field of Ethernet technology. The maximum power supply per port is 15.4W.
The main power supply characteristic parameters of the IEEE802.3af standard power supply system are:
The DC voltage is between 44 and 57, with a typical value of 48V.
Typical operating current is 10~350mA, typical output power is 15.4W
Second, IEEE802.3at, with the emergence of high-power applications such as IP cameras, video and video surveillance systems, the power supply of 12.95W obviously cannot meet the requirements. In order to overcome the power limitation of PoE, a new standard was released in 2009. IEEE802.3at, IEEE802.3at can output more than 2 times of power, and each port can supply up to 30W.
The main power supply characteristic parameters of the IEEE802.3at standard power supply system are:
The DC voltage is between 50 and 57, with a typical value of 50V.
Typical operating current is 10~600mA, typical output power is 30W
work process
A complete POE system consists of two parts: the power supply device and the power receiving device. The poe switch is a kind of power supply device, and the power supply device is the manager of the entire POE power supply process, and the power receiving device is the power supplier of the PoE switch. End (computer, network camera, etc.).
When a POE switch is deployed in a network, the POE switch works as follows:
Detection
At the beginning of the work, the PoE switch outputs a small voltage on the port until it detects that the cable terminal is connected to a powered device that supports the IEEE802.3af/IEEE802.3at standard. After detecting that the PD-end powered device is affected, the poe switch may classify the PD device and evaluate the power loss required by the PD device.
Start supplying power
During the start-up period of a configurable time, the poe switch begins to supply power from the low voltage to the PD-end powered device until 48V DC power is supplied. The PoE switch provides stable and reliable 48V DC power for the PD-based powered devices, and meets the power consumption of the PD-side powered devices that do not exceed 15.4W/30W.
Power off
When the PD-end powered device disconnects from the network, the poe switch will stop powering the powered device quickly (usually within 300~400ms) and repeat detection to detect whether the cable terminal is connected to the powered device. .

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Generally speaking, the hydrogenation reaction kettle can be divided into two categories: One is the traditional stirred reactor. Gas in the upper space of the vessel can not be circulated in the liquid phase, because of the miscibility and density difference of the gas and liquid. The unreacted gas accumulates in the upper space of the reactor in the reactor, which seriously affects the reaction rate.The other is the reaction kettle in which the gas is circulated in the liquid phase. Gas-liquid reaction is a kind of reaction often encountered in petrochemical, fine chemical, biological chemical and pharmaceutical chemical industries. Typical applications include catalytic hydrogenation, catalytic oxidation and fermentation. The common characteristic is that the contact area between gas and liquid significantly affects the reaction rate.

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