Basics of communication with Industrial Ethernet
1.3 Technologies of Industrial Ethernet
Industrial Ethernet
42 System Manual, 09/2019, C79000-G8976-C242-10
802.3af (also 802.3at type 1 or PoE)
802.3at Type 2 (also PoE+)
Power management When the connection is first established,
3 power classes are negotiated
When the connection is first
established, 4 power classes are
negotiated or there is continuous
negotiation in steps of 0.1 W
Reduction of the maximum operating tem-
None 5 °C for an active mode (2 pairs)
A
Supported modes Mode A (endspan), mode B (midspan) Mode A (Endspan), mode B
Modes
● Mode A
Phantom power via the data wires with
– 10BASE-T
– 100BASE-TX
– 1000BASE-T
● Mode B
Wire feed in via the unused wires with
– 10BASE-T
– 100BASE-TX
In both cases, a 4-pair Ethernet cable is required since the contacts 4-5 as well as 7-8
are used for power supply. All cables CAT 5, CAT 5e, CAT 6, CAT 6
A
and CAT 7 fulfil this
requirement.
Safety circuit to protect devices without PoE capability
To ensure that you do not damage any devices without PoE capability by using PoE or
PoE+, a safety circuit is defined:
● If the PSE identifies a resistance of 25 kΩ between the power wires, the end device is
capable of PoE. The power voltage is raised slowly by the PSE.
● If the PSE detects other resistance values, the power is not increased, or it is turned off.
Classification of the power sourcing equipment (PSE)
● Endspan
With Endspan, the power is supplied via a switch that can reach a device over Ethernet
cables. The switch must be capable of PoE. The two modes can be used in parallel if the
devices with PoE capability support this.
● Midspan
Midspan is used when the switch is not PoE-compliant. The power is supplied by an
additional device between the switch and end device. In this case, only data rates of
10/100 Mbps can be achieved because the power is supplied via unused wires.
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