Power over Ethernet (PoE)
2012/8/23 view:
Power over Ethernet (PoE)
Calculating the total power needed
There are currently two standards for PoE: 802.3af allows for a maximum of 15.4 W per channel, whereas PoE 802.3at doubles the available power to 25 W.
To ensure that sufficient power is available per switch, you need to calculate the total power consumption requirements for all equipment that will be connected to a specific switch on a network. This total wattage requirement must be less than the switch’s PoE power budget – total PoE power per switch and per port.
Figure 7 describes minimum and maximum power consumption levels required for both the Power Sourcing Equipment (PSE) and the Powered Device (PD).
| Class | Usage | Power Level Output at the Power Sourcing Equipment (PSE) | Maximum Power Levels at the Powered Device (PD) |
| 0 | Default | 15.4 W | 0.44 - 12.95 W |
| 1 | Optional | 4.0 W | 0.44 - 3.84 W |
| 2 | Optional | 7.0 W | 3.84 - 6.49 W |
| 3 | Optional | 15.4 W | 6.49 - 12.95 W |
| 4 | Valid for 802.3at High PoE | 30 W | 12.95 - 25.5 W |
Figure 7. The table shows the minimum and maximum power levels for PSEs and PDs. Use these values when calculating the power budget of a system.
Determining the appropriate PoE
The PoE powering of a device becomes more critical depending on temperature. Many devices can function at different low temperature levels based on the amount of power available. It is imperative to verify that the correct midspan is used for exterior cameras. As seen in Figure 8, when high PoE is used, the AXIS P1344-E can operate at temperatures down to -40°C.
| Power |
AXIS P1343/P1344/P1346/P1347: 8-20 V DC or Power over Ethernet (PoE) IEEE 802.3af AXIS P1343/P1344: max 6.4 W, PoE Class 2 AXIS P1346: max 9.6 W, PoE Class 3 AXIS P1347: max 9.0 W, PoE Class 3 AXIS P1343-E/P1344-E/P1346-E/P1347-E: PoE IEEE 802.3af max 12.95 W or High PoE max 25.5 W |
| Connectors | RJ-45 10BASE-T/100BASE-TX PoE; 3.5 mm mic/line in, 3.5 mm line out; terminal blocks for power, 1 alarm input and 1 output |
| Edge storage |
SD/SDHC memory card slot (card not included) Support for recording to network share (network-attached storage or file server) available in firmware version 5.40 and up |
| Operating conditions |
AXIS P1343/P1344/P1346/P1347: Humidity 20-80% RH (non-condensing); 0°C to 50°C (32°F to 122°F) AXIS P1343-E/P1344-E/P1346-E/P1347-E: -30°C to 50°C (-22°F to 122°F) with PoE; down to -40°C (-40°F) with High PoE |
Figure 8. The table shows that when high PoE is used, the AXIS P1344-E can operate at temperatures down to -40°C.
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