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All-round interpretation of POE switches (middle)

2022-08-03 06:20:00 【nginx】

POEHow to calculate power distance
only for complianceIEEE802.3af/at 标准PoE设备
① The influence of the network cable on the power supply distance
First let's look at the table belowIEEE802.af和IEEE802.3at标准中对Cat5eNetwork cable requirements：

说明：Type 1 value和Type 2 value 分别指IEEE802.3af和IEEE802.3at的要求.
从表中可以看出：100米cat5eEquivalent impedance of network cableIEEE802.3at须小于12.5欧姆,而IEEE802.3afneeds to be less than20欧姆.
结论一：PoEPower distance is closely linked with Ethernet cable,The lower the impedance of the network cable, the longer the transmission distance,Let's talk about the internetPoEPower distance are all play rascal！To power far enough,Network cable must first buy genuine.
② IEEE 802.3af/at标准对PoESupply Voltage Requirements
PoE输出电压范围44-57V,PDPower receiving voltage range36-57V,802.3af/at标准;参考如下：

结论二：PoEThe power supply far distance requirements,The output voltage must be high.
总结：要想PoEThe power supply distance is far enough,The network cable must meet the standard,PoEThe output voltage of the power supply product is within the standard（44-57V）尽量高.
例如：Hailing OptoelectronicsPoEThe product uses an output voltage that is55V, in the standardCat5e 200The equivalent impedance of the meter network cable is25欧姆,AFStandard current is300mA,U=0.3*25=7.5V, 55V（PoE输出）-7.5V（Attenuation voltage）=47.5V（200M line voltage of the load）,根据P=UI, 最终得出200Meter network cable load end powerP=负载端电压U*AF标准电流I=47V*0.3A= 14.1W,enough bolt or wirelessAP工作了.
Of course, a robust network does not just look at long enoughPoE供电距离,Network transmission quality must be guaranteed.根据IEEEIt is stipulated that the network cable transmission exceeds100米,Transmission quality is not guaranteed,但是在有的情况下（成本压力下）,For example, when installing a camera,We will be more than a dozen meters,Here's a little trick for you：For more than not too many cases,Manually set the connection rate of the camera to10M,对于1个200megapixel gun,10Menough speed,Very high chance to solve the problem.
POEswitch power
PoEThe total power of the switch is a very important indicator,It's directly related to how many cameras you can bring.The mains power is400W的、24端口的PoE交换机来说,After removing the lossPoEThe total power of the switch is approximately370W.
在IEEE802.3af标准下,it can fill24个端口（370/15.4=24）,that can be given at the same time24A camera power supply,That is, full power supply.但如果是按照IEEE802.3at标准的单口最大供电功率30W计算,同时最多就只能给12个端口供电了（370/30=12）.
实际使用中,Many common webcams have lower maximum power consumption,基本不超过15W,如果这时每个PoEPort according to the maximum power（比如30W）To reserve power,就会出现有的端口PoE功率用不完,而有的端口却分不到功率的情况.比如,有些PoEAll switches support dynamic power allocation,可以避免这种情况.在选购PoE交换机时,Depends on whether the switch supports dynamic power allocation,This way each port only allocates the power actually used,这样就能更高效地利用PoE交换机的供电功率.



Network Monitoring Project,Different from ordinary network cabling,Very large amount of data transfer,功率高,and require 24/7 non-stop work,quality assuredPoEEquipment and wire is the assurance of the whole system stable.

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