Profibus line redundancy with Westermo optical ring
I've been trying to setup an optical redundant ring using Westermo fiber optic modems W612, but if I connect line A to ring node 1 and line B to ring node 2 (node 3..n have dp slaves connected) then the optical ring cannot handle properly the communication due to data being sent on both lines.
Then I've found that Abb profibus manual states:
The optical ring in combination with the line redundancy can only be set up by
using the optical link module “OZD Profi 12M” from Hirschmann. Other optical
link modules will get collisions of data frames that results in a complete disturbed
communication on the PROFIBUS.
Anyway what I find strange is that it can communicates ok for long periods (and if I use a profibus analyzer the line doesn't seem to be disturbed) but then the line drops and it will not restore until i disconnect line A (or B) from the ring. I tried to change timeouts parameters for the nodes, setting different values for node 1 and node 2 but anyway once the line drops it doesn't automatically restore.
Any experience/thoughts? Adding a RLM seems useless because it doesn't increase the availability.
I found this info in ‘OZD Profi 12M’ manual, section 5.2.2 systematic trouble shooting page 38,
Check if these helps …
Redundant optical ring
- Both channels of all the OZD Profi 12M … PRO must be set to “Redundant optical ring” operating mode.
- All the OZD Profi 12M … PRO within a ring must be optically linked with one another.
Configuration (these settings can usually be set on the PROFIBUS master using configuration software, not on the OZD Profi 12M … PRO):
- Slot time configured correctly? (for basics, see chapter 3.2; for calculation, see “TSLOT.exe”)
- Retry value configured correctly? (target value > 3, see chapter 3.2)
- Value of MIN TSDR configured correctly? (target value > 11, see chapter, Retry)
- In case of redundant optical ring only: “HSA” (Highest Station Address) configured correctly or “a non-existent bus subscriber” configured?
Note: It may be necessary to perform a reset on the device on which the parameters have been changed (e.g. master) so that the new values can also be transferred!
Before changing configuration of master parameterization I recommend you to take backup of current parameter settings, will be easy to fall back quickly to old config. if required.