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DeviceNet Troubleshooting

DeviceNet will not function correctly if design rules are not followed. Even a Network previously thought to be functioning correctly may begin to exhibit abnormal or anomalous operations due to incorrect system design.

Termination Resistors

A termination resistor equal to 121 Ohms 1%, 1/4W must be attached at each end of the Trunk cable. The resistors must be connected across the BLUE & WHITE wires of the DeviceNet cable.

By disconnecting the resistor connection, DeviceNet energy, and using a measuring device from Can_H & Can_L (BLUE and WHITE Wire), resistance values can be measured in ohm range, the reading should be approximately 60 Ohms. The Devicenet network will not work properly without terminating with resistance.
Even if it works in short network networks, it can cause problems from time to time.

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DeviceNet Network Grounding

The DeviceNet cable should be grounded in one place only. This is very important, although your DeviceNet network seems to be working while commissioning, your line may be disconnected from time to time due to grounding and you may not be able to see other node addresses. When you power off the DeviceNet energy and give it back, your network can continue to work, but it may cause problems again in the future.
Grounding should be done at the closest place to the center of the DeviceNet network. Connect to the ground using 8 AWG wire up to a maximum length of 3m (10Ft). And connect the (BLACK Wire) to the DC ground of the power supply to this ground connection.


Power Source

A DeviceNet network requires a 24VDC power supply. Use a power supply rated 24VDC (+/- 1%). Make sure that the power supply has its own current limit protection. Provide fuse protection for each part of the wiring system. The power supply must be of the correct size to provide the required power to each device.

The thin wire mainline can only handle 3 amps, the thick wire mainline can physically handle 8 amps. Multiple power supplies can be installed in a DeviceNet network, but no more current than the appropriate value should flow in any cable section. An important note, when installing more than one power supply in a network. Break the RED V + wire between the power supplies. This effectively isolates the power sources from each other.

Common mode voltage can sometimes be a problem in DeviceNet networks that have extra long main lines and/or devices on them, drawing large currents over longer distances. Communication problems can occur if the voltage on the BLACK V-cable differs by more than 4.65 volts from one point of the network to another.
if the voltage between the RED V + wire and the BLACK V wire drops below 15 volts, then the common-mode voltage can adversely affect network communication In an existing network. Add an additional power supply will fix common voltage problems.

It is recommended that the DeviceNet power supply be used only to power the DeviceNet network. If more than one power supply is required, verify that the V + link between the sources is broken.

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Use the ohm range of a gauge to measure the resistance between V + and Can-H V + and Can-L V- and Can-H V- and Can-L. All of these impedances must be greater than 1 M ohm.

Always check your connections and voltages. Most DeviceNet faults are caused by termination resistors and voltage.