Marty,
1. sure (please use 2 cables to extend)
2. one Extender cable vs. two Extender cable
3. if you have redundant Controller setup, you should always use 2 cables on all the extenders
Please always keep an eye on you max. bus length :-)
Hope this helps,
Klaus
In reply to Klaus Erni:
Yes, thank you Klaus. The Product Data Sheet for the S-series Horizontal Carriers (www2.emersonprocess.com/.../PDS_S-series_Horizontal_Carriers.pdf) should be updated to clarify this in the table for Ordering Information which lists Description/View/Model No.
Marty
In reply to putelism:
sorry, what's wrong with what is currently shown there please ?
2-Wide Power/Controller Carrier with Dual Extender Cables 1.1m (43 in)
SE3051C2
2-Wide Power/Controller Carrier with Single Extender Cable 1.1m (43 in)
SE3051C3
The pictures even show one or two cables !
Klaus,
Nowhere in the product bulletin does it explain why you would use the extender with one cable or the extender with two cables.
The two description fields should be embellished to explain "Used with a simplex controller setup" or "Used when controller has redundant backup".
While it may seem obvious to you, we had several end-users, one of them a client, asking the same question: "when do you use which one?"
Way back when, the dual extenders were released to satisfy a customer requirement for dual cabling. The dual cables provide some level of increased availability as an open circuit on one cable will not result in loss of IO functionality. The cables are simply parallel paths, so if one is disconnected, communications still works. There are no diagnostics on these two connections, so if one cable does fail, you might not know about it. If a cable does open circuit, you will not know it unless to test the cables or the second cable also fails in a similar manor. For instance, if one bank select line open circuited on one cable, the same line would need to fail on the second cable to actually affect the system. These are passive cables and the likely hood of failure is low, and the likely hood of the same failure on a pair of cables highly unlikely.
I indirectly agree with Klaus, that if you have redundant controllers, you are concerned about availability, you would likely want to use the dual cables to gain some increase over simplex cable. However, the choice of using the dual cables or simplex is independent of whether you have simplex or redundant controllers. The dual cables work equally whether the controller is simplex or redundant.
Andre Dicaire
In reply to Andre Dicaire:
Andre,
Thanks for the explanation. I had told my client the dual cabling was recommended for redundant controllers, when it has nothing to do with controller redundancy. it is merely redundant cabling: period. I will pass along this information to client.
If there is no redundant circuitry on the 8-W carrier, then it is still the single point of failure in the architecture, even if the redundant cabling option is utilized. Right?
Just to be clear.
1. The redundant cabling is used to increase the MTBF for the cabling only. Even though it contains only passive components and already has a high MTBF, this will increase it, yes?
2. There are many active components in a controller. The redundant controllers are used to increase the MTBF for the controller(s).
3. There is no physical relationship between the redundant controllers and redundant cabling. The system MTBF is only as good as its weakest component; or smallest MTBF.
(I see you responded at 1:10am? ..... get some sleep!)
1. Yes. The dual cables address some failure modes, so MTBF of cables is higher. For some customers this has been a requirement, especially if the cables extend to an adjoining cabinet (still limited to 21 ft LocalBus Limit)
2. True. Controllers might also be made redundant to facilitate upgrading of firmware.
3. Correct. just as there is no physical relationship between a redundant IO card and a redundant controller. each is evaluated as to its contribution to overall availability.
(I'm in Mountan Time zone...)