Something on AB DH+ network connection need clarification

[ckchew666]

Hi,

Our customer plant has about 20 nodes of PLC running in DH+. Everything has be running fine for couple of years. Recently when they purchase the RSLogix 5 and go online with the PLC thru 1784-PCMK from the network programming port, some of the PLC will shutdown itself. The PLC that shutdown may varies. Previously customer is using the DOS programming software and everything is fine.

We went to the site and check their connection/wiring, we found out that the daisy chain DH+ network is fine, but there is a point where the programming port is tap direct for a node (terminal block)). This is where the particular node has 3 wires, 2 for the DH+ daisy chain and another cable for programming port (to hook up our notebook).

I'm not sure if this is correct or wrong.

Question:

1) We ask our customer to daisy chain the programming port at the end of the node, but the terminator resistor should be located at the last PLC or at the porgramming port (9-pin)?

2) The customer do argue that tapping a programming port from one point/node is the same concept as the 8-pin Mini DIN port on the PLC-5 CPU where they are shared. For example Channel 1A of a PLC-5/40 has a 8-pin Mini DIN (programming) & a 3 pin DH+ (networking). Can anyone please clarify me how's the 8-pin Mini DIN (DH+) port of the CPU work?

Thanks in advance

 

[brucechase]

What do you mean by shutting down? If the PLC is dropping communications, I have seen, experienced, and still curse it every day. No one has ever been able to help.


http://www.plctalk.net/qanda/showthread.php?t=10666

Here is the post where I first asked the question. I know this isn't the answer you wanted, but I'm not sure if you are having the same problem as I am.

 

[yam785]

Brucechase I agree with.

I deal with it quite alot. Especially with Windows NT. It closes RSLogix when it happens. I deal with it a least a couple times a week.

My best answer is deal with it til they fix it.

 

[Unregistered]

Make sure the bus address of the PCMK is up and out of the way of the process devices - if you have a duplicate network address , this can cause horrible things to happen.

 

[jbklyman]

DH+ programmer tap

I have a smaller DH+ network with 2 SLC-500 systems and a Panelview display. At the end of the DH+ line (by the control room) I installed a 171770SC Data Highway Station connection box. This is a little metal box about 8 cm cube with a couple of terminal block connections inside. This box holds the DH+ termination resistor, and allows you a T-tap or programmer/workstation drop line. The "tap" line box is the equivalent of a SLC 5/04 processor that allows you to access the DH+ highway via the Mini-DIN connector going to your workstation, while the 5/04 is connected to the "Blue Hose" or 3 wire DH+ cable that runs in a daisy chain configuration to the rest of the processors and DH+ appliances.
This Tap allows you to connect and disconnect a programmer workstation without disturbing the DH+ cabling or termination resistors. This similar type of DH+ data tap is available on the PLC-5 systems.
I have not had any experiences with this disrupting my network, but it is a small network, and I don't have much other experience other than the two A&B Plc systems I've dealt with. Hope my explaination of the DH+ network and T-taps helps.

 

[jimtech67]

jbklyman

What is the part number for the Data Highway Station connection box i could not find it on the AB web site

Jim

 

[rsdoran]

Jim I think its 1770-SC http://literature.rockwellautomation.com/idc/groups/literature/documents/td/1770-td020_-en-p.pdf#xml=http://127.0.0.1/texis/search/pdfhi.txt?query=1770-SC&pr=literature.rockwellautomation.com&prox=page&rorder=500&rprox=750&rdfreq=0&rwfreq=0&rlead=250&sufs=1&order=r&cq=&id=41ff2c8717

 

[ckchew666]

I have a smaller DH+ network with 2 SLC-500 systems and a Panelview display. At the end of the DH+ line (by the control room) I installed a 171770SC Data Highway Station connection box. This is a little metal box about 8 cm cube with a couple of terminal block connections inside. This box holds the DH+ termination resistor, and allows you a T-tap or programmer/workstation drop line. The "tap" line box is the equivalent of a SLC 5/04 processor that allows you to access the DH+ highway via the Mini-DIN connector going to your workstation, while the 5/04 is connected to the "Blue Hose" or 3 wire DH+ cable that runs in a daisy chain configuration to the rest of the processors and DH+ appliances.
This Tap allows you to connect and disconnect a programmer workstation without disturbing the DH+ cabling or termination resistors. This similar type of DH+ data tap is available on the PLC-5 systems.
I have not had any experiences with this disrupting my network, but it is a small network, and I don't have much other experience other than the two A&B Plc systems I've dealt with. Hope my explaination of the DH+ network and T-taps helps.

This connectors can be use with a network which has SLC, PLC5, CLX & PKTX right? As long as they are DH+. From what you explain, looks like there is some PCB board inside the box to control the data flow, otherwise we can make the t-tap/box ourself?
I'm sorry I have not seen the box myself, hope u can explain more. Thx.

 

[504bloke]

This connectors can be use with a network which has SLC, PLC5, CLX & PKTX right? As long as they are DH+. From what you explain, looks like there is some PCB board inside the box to control the data flow, otherwise we can make the t-tap/box ourself?
I'm sorry I have not seen the box myself, hope u can explain more. Thx.

It has no circuit board inside, just a connector strip (from memory!) so you could make this yourself, It has a capacitor (I THINK, cant remember!) that is connected to one leg of the DH+ to earth........

I have one at work and can post a picture later today for you if required.

 

[ckchew666]

It has no circuit board inside, just a connector strip (from memory!) so you could make this yourself, It has a capacitor (I THINK, cant remember!) that is connected to one leg of the DH+ to earth........

I have one at work and can post a picture later today for you if required.

Appreciate if you can post a pic here, not jst for me, everyone interested can hav a look also. Thx in advance

 

[tom_stalcup]

repeating a question

Is the problem with the plc's shutting down, or just the communications being lost on the plc's?

 

[ckchew666]

Is the problem with the plc's shutting down, or just the communications being lost on the plc's?

I'll check with our cust. & make a trip there to verify....be right back

 

[jimbo3123]

Your programming ports should be daisy chained, just like processors. There should never be 3 wires going to a single node unless there is circuitry there to seperate that traffic (like on the processor itself).

 

[JesperMP]

Avoid using "T" branches on the DH+ network. Allways daisychain.
This also means do not use the special grey box that other posters refer to. I remember seing an article in an AB magazine explaining that T branches should be avoided. The article also described how a customer had resolved serious DH+ problems by removing the T stubs.

To find out if this is connected with your problems, try to go online via the mini-DIN connector on one of the CPUs. If that works without problems, then you have a good indication that the T stubs are to blame.

Another cause could be connecting different power supplies (control voltage to the PLCs, and office voltage to the laptop). Try to connect the laptop on battery power only, or try to have a supply for the laptop that comes from the same source as the control voltage.