EtherCAT "listen only" device

I have an integration challenge where a [black box] control system is controlling, among other things, a Yaskawa Sigma 7 servo controller on EtherCAT.

My goal is to read the absolute position of the Yaskawa servo's absolute encoder. I know that's part of the EtherCAT data being exchanged between the two, and that the Sigma 7 uses the CiA402 Drive Profile, so parsing the data should be do-able.

My reading of the data doesn't need to be fast; it's literally going on an HMI screen. A quarter second would be plenty.

I know I could try a Hilscher NetTAP NT151-RE-RE and ask them to write the encoder position to it as an EtherCAT slave, then I can read it as an EtherNet/IP slave (I'm running a CompactLogix).

But does anyone know of an EtherCAT device that can "listen" to things like the CiA402 profile connection passively, once it's identified between two devices ?

My hunch is to look at some small Beckhoff controller that is an EtherCAT master (like all Beckhoff controllers) and can be an Ethernet/IP slave via EL66-something module.

This is at a crude concept level of course. Also Omron NJ (?) PLCs are ECAT masters (certainly work with Yaskawa drives!) and communicate on EIP.

Hello Ken: I have been working in EtherCAT slave (don't like this word too much, but this specification still call field devices like this) development for some years and have some understanding of the EtherCAT specification, less so though than CIP or PROFINET, so please take my comments preliminarily.
I am not aware for EtherCAT of any listen-only messaging capability for redundant scanners like EtherNet/IP or "shared-device" in the case of PROFINET IO.
If you were talking about something that would be possible to sell in large numbers, I can think of a number of alternatives, but your post is clearly for this one installation you need to setup, so will not go into further details, as this would entail costly development and long lead time.
Since the EtherCAT master is a black box, and all you can get is for the machine builder in charge of that system to add another EtherCAT node and map the data you need from the master application, I think the one gateway from Hilscher you already identified is one of your options. Their arch-rivals (HMS Networks) has a similar product, but is the same idea, EtherCAT slave to EtherNet/IP adapter. Then it is a matter of which product is better supported where you are, which has better price and so on. Good luck with the integration.

Maybe this thingamabob could enable you to "sniff" the data on the Ethercat bus:
https://beckhoff.de/english/ethercat/et2000.htm?id=177466180346
It is stated to support Ethercat.

I tried to see if there is an alternative way to connect to the Yaskawa servo controller, so you can retrieve the data without affecting the Ethercat bus.
It seems that yaskawa's sites are down at the moment.

Outstanding advice, folks ! None of those were things I had considered or known about.

Alfredo, your comments about the absence of a "listen only" mode are important. I've literally never used EtherCAT and the risk of making assumptions about its similarity to EtherNet/IP are high.

My client has allowed me some more access to the OEM engineers so I may be able to do this the easy way by cooperating instead of competing !