Maintenance Technology August 2016 - (Page 41)
Choose quality components.
Select high-quality, shielded CAT6 cables. When
choosing an Ethernet switch, purchase from a
quality supplier. As for Ethernet connectors,
specify industrial-grade devices. Don't try to
save a few dollars by using office-type connectors. The extra money spent will pay dividends.
A dead Ethernet switch or bad connector will
take your system down.
Use full-duplex industrial-rated switches
rather than hubs.
An Ethernet switch routes the packets only to
the appropriate destination. A hub spits out
the data to every node on the network. Thus, a
switch is clearly more efficient.
JIM DAVIS OF MOTION INDUSTRIES (motionindustries.com) has some
practical advice for personnel dealing with Ethernet issues on the plant floor.
He knows what he's talking about. Davis manages the company's Automation
Center in Countryside, IL. Among other things, he brings 38 years of realworld electrical experience to the table and holds four U.S. patents.
As a point of reference, Davis notes that Ethernet has become the de facto
standard in control-system communications, and equipment vendors are
increasingly including it and its variants in automation equipment. Since the
protocol's formalization as a communications standard (IEEE 802.3) in 1983,
Ethernet data rates have increased from 2.94 megabits/sec. to 100 gigabits/sec.
A 400-gigabit/sec. version is expected in late 2017.
For motion-control and time-critical applications, there's a version of
Ethernet called IEEE1588. This system uses a timing scheme to insure that data
packets arrive in a timely and predictable manner.
Standard Ethernet is commonly referred to as TCP/IP. The four main
industrial-control versions are: EthernetIP, EtherCAT, ProfiNEt, and Modbus
TCP. These protocols take the regular version of Ethernet and add layers of
control to allow industrial controllers to efficiently talk to each other. Standard
Ethernet is not deterministic, i.e., you don't know exactly when a data packet
is going to arrive. The industrial versions, however, have various means of
insuring data determinism.
Davis offers these best-practice tips for working with Ethernet in plantcontrol systems. Following them should lead to trouble-free service.
Route cable properly.
Be sure to keep any Ethernet cables well away
from higher voltage and/or noisy conductors.
For example, it's not a good idea to run those
cables next to 460-VAC motor wiring. Always
use dedicated conduits for Ethernet cables in a
Troubleshoot the system.
When starting up a system, ping all of the IP
connections first. Ping is a command on your
PC to "find" the IP node. To ping a device, go to
the "search programs and files" dialog on your
PC, type in the word RUN, and press enter.
The RUN dialog box will open. Type the word
PING followed by the IP address you are testing.
For example, if a PLC has an IP address of
192.168.45.1, type PING 192.168.45.1 and press
enter. If you see a dialog box with "request timed
out," this means that your PC cannot find the
node. You may have an incorrect setting in your
device or a faulty connection. If your ping test
is successful, you will see a series of messages
similar to this: Reply from 192.168.45.1: bytes =
32 Time <1ms TTL = 128. This message denotes
that the node 192.168.45.1 is on your network
and can send/receive data. If you want to ping
your own PC, use an address of 127.0.0.1.
Document your system.
Document every node on the network. Include
the physical name ("PLC," "PUMP DRIVE
#1"), its IP address, subnet mask, and gateway
address. Make sure to label the control panel
with the IP, subnet, and gateway information for
the Ethernet items within. This information will
be critical if a component fails and needs to be
For more information on industrial-control networks, visit motionindustries.com and the MiKnowledge Hub
MAINTENANCETECHNOLOGY.COM | 41
Table of Contents for the Digital Edition of Maintenance Technology August 2016
On The Floor
Accepting The Challenge
Advanced Software In The Jungle
Put Efficiency in MRO Storerooms
Rethink Overall Vibration Monitoring
Reliable Pumping Supplement
Practical Oil Analysis: Why and What For?
SAP Tips and Tricks
Compressed Air Care
Nurture STEM Learning
Heed Drive-Belt Temps
Internet of Things
Maintenance Technology August 2016