View Single Post
Old January 10th, 2020, 04:13 PM   #4
Ken Roach
Lifetime Supporting Member + Moderator
United States

Ken Roach is offline
 
Ken Roach's Avatar
 
Join Date: Apr 2002
Location: Seattle, WA
Posts: 15,221
Quote:
I measured the reisitance it shows around 160 ohm .
DeviceNet networks require two termination resistors of 120 ohms each, connected between the CAN_H and CAN_L wires (Blue and White for DeviceNet) at the physical extreme ends of the network trunk.

Unlike Profibus, most DeviceNet products do not have a built-in termination resistor or simple switch to enable a terminating resistor. Most DeviceNet networks that involve VFDs use open-style connectors, and the resistors are easily visible wherever they are installed.

Because the CAN signal itself will interfere with an ordinary multimeter, you should shut off the DeviceNet 24V power before making this measurement.

Two 120 ohm resistors in parallel will give a combined resistance of 60 ohms; that is an ordinary Kirchoff's Rule calculation. The additional resistance of the DeviceNet transceivers makes the total parallel resistance a little less; a system with 14 drives should be measured at about 50-55 ohms.

A measurement of 160 ohms suggests that no terminating resistors, or resistors of the incorrect value, have been installed.

DeviceNet will often run without terminating resistors installed, which leads some users to believe that they are not required. This is not true, and you should do no more troubleshooting until you have verified that one 120 ohm terminating resistor has been installed at each physical end of the DeviceNet trunkline.

Two resistors. 120 ohms each.

Not zero, one, or three.

Not 150 ohms, or 82 ohms.

Last edited by Ken Roach; January 10th, 2020 at 04:18 PM.
  Reply With Quote