We are executing a project wherein there are four control rooms having HIS. For ethernet communication we have used thicknet 10 Base 5 cable as backbone. From this backbone cable we are dropping AUI Cables using piercing type transceivers to Hubs in each control room. Hubs are having AUI ports for backbone connection. Since the distance between control rooms is more than 500 meters, we have used one ethernet repeater also.

The ethernet communication breaks intermittently and communication with any one or two HIS goes unhealthy. This is happening intermittently.

Please advise a solution.

Regards.

 

I am surprised that you can still get parts for 10Base5 Ethernet cable. It is many years out of date. Using this cabling system causes several
problems.

1. The piercing or vampire taps are unsuitable for industrial use. Any vibration or corrosion can cause contact failure.

2. Your entire network is a single collision domain. You could be suffering from loss of messages from a network that is just too busy. I witnessed this occur in the Denver Airport baggage handling system.

3. One repeater for 500 meters is not adequate; you are probably experiencing intermediate signal loss. Using more repeaters also introduces more likelihood of error.

Recommendations

a. Rip out all 10Base5 coaxial Ethernet cable and switch to Cat5E cable except for the 500 meter run.

b. Install a top level Ethernet switch at the Yokogawa DCS. I think you can buy a switch with a 10Base5 port and all other 10BaseT ports. There are also switches with fiber optic ports to reach your most distant control room.

c. Install an Ethernet fiber optic link to replace the 500 meter run.

d. Purchase industrial grade 10/100BaseT Ethernet switches for each control room. Hirshmann, SixNet, Cisco, 3Com, etc.

This will segment the network so that signals for each control room stay only in that control room. Your flat Ethernet now allows every message to travel through the entire network causing collisions. While your Yokogawa DCS cannot provide more than 10 Mbps, it can easily be converted to 10BaseT.

Dick Caro
============================================
Richard H. Caro, CEO
CMC Associates
2 Beth Circle, Acton, MA 01720
Tel: +1.978.635.9449 Mobile: +1.978.764.4728
Fax: +1.978.246.1270
E-mail: [email protected]
Web: http://www.CMC.us
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Check the piercing taps and backbone grounding for
physical problems. Connections are the #1 source of problems. A ethernet monitor would be good for
protocol problems, collisions, a chatting stack or
tranceiver, etc.

Regards

cww

 

Hi NJ,

To be quite blunt pull out the 1970s technology and put in a modern Ethernet system using optical fibre.

Otherwise, the piercing taps could well be the problem. These were never a great idea because of the potential for poor connection between the tap and the centre conductor of the cable.

The other thing to look at is to ensure that both end of each cable are terminated in 50 resistors. Remove the resistor at one end and put your
multimeter across the cable. You should see 50 ohms. Replace the resistor and go to the other end of the cable and repeat.

If the results look odd (out by more than a few ohms) then check the resistors. If they look OK then you can get a time domain reflectometer
(TDR - works like radar) and check the cable for faults. The TDR will give you the location of any cable faults in distance from the TDR.

Regards

Peter Whalley
Magenta Communications Pty Ltd
Melbourne, VIC, Australia
e-mail: peter*no-spam*@magentacomm.com.au
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