1784-PKTX DH +connection

[meghnesh]

Hi All,

A quick question.

I have one Computer with 1784 PKTX Card for interfacing with DH+ Network.

One PLC nearby control room has got:-
1. 2 Nos. of DH+ Cable coming from the field and Terminating at DH+ connector at PLC

2. One DH+ cable going to the PKTX card from the same PLC's same DH+ Connector.

So the PLC connector has got 3 DH+ cable.

CAN I HAVE ONE MORE DH+ CABLE FROM THE SAME PLC's SAME DH+ CONNECTOR GOING TO A DH+ to ETHERNET GATEWAY ?

 

[JesperMP]

DH+ is a daisy-chain type network.

There can only be 2 cables going into 1 connector, or 1 cable + termination resistor into 1 connector.

T's or stubs are not allowed.
(There exists a special box that can be used to make a T joint, but even with the special box it is not recommended.)

 

[meghnesh]

Hi,
Thanks for your reply.

But I have seen at site the DH+ connector had total 3 cables. How did that worked i am wondering?
And can you suggest me a device like a TAP or something of Rockwell make ?

 

[JesperMP]

It may work even if it is connected improperly, but it is not to be encouraged.
Forget making T-junctions.
Make it the right way, it is not difficult.

 

[Ken Roach]

It is very common for installers to violate the wiring guidelines for DH+.

A short "dropline" like the one you describe frequently works well on DH+. DH+ technology is very robust and tolerant of poor signal quality.

But it's still technically against the installation guidelines.

 

[meghnesh]

ok so can you please suggest me a DH+ Tap..a catalog number or something ?

 

[Ken Roach]

The old Allen-Bradley "tap" was the 1770-SC Station Connector. These have not been built for many years, and are really just a box with terminals and a small capacitor inside.

If you think the "dropline" is the problem, you can just eliminate the dropline by running the DH+ cable out to the 1784-PKTX, then back to the PLC.

 

[Ken Roach]

If you're interested in the formal installation rules for DH+, they're in the old Data Highway Cable Planning and Installation Manual:

http://literature.rockwellautomation.com/idc/groups/literature/documents/um/1770-um022_-en-p.pdf