Inspection device and method for powered devices in a power over Ethernet system

An inspection device of power source equipment for detecting a powered device of a power over Ethernet system, wherein the power source equipment comprises a connecting port adapted to connect to the powered device through a network wire, and wherein the inspecting device connects to the connecting port, the inspection device comprising:

• an inspection computing unit that controls application of a plurality of testing voltage signals to the connecting port, whereas the plurality of testing voltage signals comprise, sequentially, a first voltage V1, a second voltage V2, a third voltage V3 and a fourth voltage V4, wherein the first voltage V1 and the third voltage V3 are substantially the same, the second voltage V2 and the fourth voltage V4 are substantially the same, and an application period for the fourth voltage V4 is a sum of an application period for the second period V2 with an extension period;
• a power supply that supplies the plurality of testing voltage signals to the connecting port;
• and
• a current measurement device that measures at the connecting port a first current I1 after a predetermined period following applying the first voltage V1, measures a second current I2 after the predetermined period following applying the second voltage V2, measures a third current I3 after the predetermined period following applying the third voltage V3, and measures a fourth current I4 after a time period, which is longer than the predetermined period, following applying the fourth voltage V4, wherein
• the inspection device calculates a first resistance by Rdet1=(V1-V2)/(I1-I2) and a second resistance by Rdet2=(V3-V4)/(I3-I4);
• and
• the inspection device determines that the connecting port is not connected to a suitable powered device if (1) any of the first current I1, the second current I2, the third current I3, and the fourth current I4 exceeds a first predetermined value, or (2) ΔRdet=Rdet1-Rdet2 is greater than a second predetermined value, and otherwise determines that the connecting port is connected to the suitable powered device.