Why Does My EtherCAT Expansion Chassis Not Work with a Longer Cable?

Updated May 3, 2018

Reported In

Hardware

  • NI-9144

Issue Details

I have been using an NI 9144 EtherCAT expansion chassis with my CompactRIO without any problem. I have now added in a longer cable and suddenly I can't see my modules. Why is this happening and how can I fix it?

Solution

The EtherCAT standard allows a maximum cable length of 100m between the CompactRIO controller and the NI 9144 chassis before a repeater is needed. If the EtherCAT modules are disappearing from the chassis despite using a 30m cable, it is generally due to the following:

1. Incorrect cable choice: If you use a shielded Ethernet Cable (STP or FTP), you may run into issues with grounding when your cables are beyond 30m in length. If shielding is not necessary for your application, use unshielded CAT 5 cable (UTP) as this will work up to 100m. If you require shielding, ensure that the shield is grounded properly and contact National Instruments if you have questions about doing so. More information about shielded and unshielded cables can be found at the Wikipedia link below. 

2. Noisy environments: If the area you are running the cable through is particularly noisy, this may cause issues with EtherCAT communications. In this case, shielded cabling may be necessary.

3. Out of date firmware: If your chassis does not have the proper firmware installed, it will not populate with modules. There is a detailed explanation of how to go about doing this contained within the NI 9144 User Guide. Please refer to the section entitled "How to Upgrade Your Firmware" which is contained in the linked document below.

If after verifying all of the above you are still having issues, please contact National Instruments.

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