Our machine has PoE ports to power cameras. How do we know there is enough power for 4 cameras, and how do 802.3af, at and bt differ?

The three PoE standards differ in power per port (measured at the source / at the powered device): 802.3af: 15.4 W / about 12.95 W. Enough for most small industrial cameras. 802.3at (PoE+): 30 W / about 25.5 W. For cameras with illuminators or small PTZ units. 802.3bt: 60 W or 90 W at the source. For high-consumption devices. Beyond the per-port standard, check the machine's total PoE budget. For example, a unit listing 4 ports at 802.3at with only 60 W total cannot supply 4 cameras each drawing 25 W. Quick calculation: take the maximum power from the camera datasheet, add any illuminator, multiply by the number of cameras, and compare with the machine's total PoE budget. Remember to add this to the power supply sizing for the computer. Many machines only provide PoE when the input voltage is at a certain level, for example 24 VDC or higher. Read the datasheet notes carefully.