How to detect EMI on Ethernet cable using BERT (bit error rate test)

How to detect EMI (electromagnetic interference) on Ethernet cable using BERT (bit error rate test)

The NetXpert XG cable tester runs two tests using BERT (bit error rate test) to see the impact of EMI (electromagnetic interference) from a motor on an Ethernet cable.

A BERT test is a powerful real world test drive of your Ethernet cable. Gigs of bits are sent across your Ethernet cable, received at the remote side, and counted for errors. The NetXpert XG is unique in that it performs a bi-direction BERT test. That is, once the bits cross the cable once, the remote sends them back across the cable again to the other side to complete a bi-direction test.

Not only will bad connectors cause problems, but after the cable is installed, environmental factors can cause data disruptions. Some common problems include cutting the insulation during installation, too tight of cable bends, running cable too close to power cables or motors, even using the wrong cable with improper or no shield.

In this video, in the first case, the Ethernet cable is far enough away from the motor that EMI does not impact the Ethernet cable data. The BERT test is run. And the BERT test passes.

In the second case, the Ethernet cable is moved closer to the motor and EMI causes interference with the data. We see the bit errors when the BERT test is run, and the BERT test fails.

BERT errors are bad because they can cause servers and PC's to slow or even disconnect. If the Ethernet is connected to a PLC (programmable logic controller) in a manufacturing facility, process plant, mill, or mine, BERT errors can cause PLC dropouts, which can cause processes or plants to stop, which can cause downtime and lost production.