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ISA EXPO 2007

•

Special Issue

News

Visit Modbus-IDA &

Modbus Members at ISA

EXPO 2007

Enter Your Ticket to Win

One of Five iPod nanos

Plan to attend the ISA EXPO next week? Cut out the

“Modbus Ticket” (shown left), and have it stamped at

each of the Modbus member’s booths at the show.

Then visit the Modbus booth (#1148) and enter the

ticket for one

of five

drawings at

the show to

give away a

new 4-GB

iPod nano. All

entries will be

eligible for a grand prize drawing in the week following

the show. See you in Houston!

Help Celebrate 30 Years

of Modbus

Communications

Modbus-IDA will celebrate 30 years of Modbus

communications in 2009. As we prepare for this, we are

turning to users and suppliers to gather information

about the far-flung uses of the most popular industrial

communications protocol in the world. What can you

tell us about your Modbus experience?

•

Who has the oldest application that is still working?

•

What is the installation with the largest number of

Modbus nodes?

•

What is the oddest or most bizarre application of the

Modbus communications?

Write in to tell us about your Modbus application. We

will be selecting stories for future publication as part of

the upcoming celebration.

Send your story to info@modbus-ida.org.

News about the World’s Most Popular Industrial Protocol

Organization News • Organization News

Meet Some of Our Members...

AquaSensors™

designs and

manufactures analytical measurement

systems for process control

applications. The company’s product

design reduces equipment and

installation

costs while

improving

reliability

in a wide

variety of applications. Current

measurements include pH, ORP, two-

electrode conductivity, toroidal

conductivity, dissolved oxygen,

dissolved ozone, resistivity, drinking

water turbidity, and suspended solids.

The patented DataStick measurement

system features pre-calibrated, plug-in

sensor heads that provide 24-bit data

and can be calibrated, configured or

diagnosed directly from a PLC or

computer system. No intermediate

analyzer boxes are necessary.

For local display and calibration of any

DataStick system, the low-cost AV38

display interface can be used.

Aquasensor’s AnalogPlus line of

analytical measurement systems features

cabled sensors with improved reliability

and accuracy. The differential pH and

ORP sensors work with any industry

standard analyzer. All AnalogPlus

sensors can also be used with the

company’s AV88 Universal Analyzer.

AquaSensors support all its

measurement systems with a full line

of mounting hardware including

tees, union mounts, ball valves,

sanitary fittings, and immersion

hardware. Sensor head wash units are

also available.

(www.aquasensors.com)

KepwareTechnologies

develops

communication products that are

known worldwide for their quality,

reliability, and ease of use. Kepware has

earned a reputation for supplying high-

performance software solutions for the

connectivity needs of the industrial

automation market. Users can

download free demo software from

Kepware’s website and reach the

company’s knowledgeable sales and

technical support associates by phone

or e-mail.

(www.kepware.com)

Fieldserver Technologies

develops

and manufactures gateways and

protocol translators that interface with

building automation systems, fire alarm

panels, process controls and other

devices and networks using the

Modbus network and systems.

FieldServer also has over 75 different

drivers interfacing to over 350 different

devices. When an integrator needs to

interface LonWorks, BACnet, Metasys,

DH+, Ethernet/IP, Profibus or a wide

range of other protocols to a Modbus

system, FieldServer has a solution.

In addition to stand-alone gateways,

FieldServer also has ProtoCessor, an

embedded Protocol Coprocessor, for

device design engineers to use to

provide proven Modbus output (serial

or TCP) from their devices. Check out

Fieldserver’s website for further

information on its various gateways and

driver protocols.

(www.fieldserver.com)

Modbus-IDA Discussion Forums

Q&A

Echo on a Modbus over

RS485 Network...

In July Pankaj Sharma posed this

question:

I have an application running on my

PC, which implements the Modbus

protocol. This application sends

standard commands to a device

running Modbus over RS485.

The way the application connects to this

device is through a USB-to-RS485

converter. I am programming this

USB-to-RS485 converter. Both the

application on the PC and the device on

the other end are tested and work

properly with a commercial USB-to-

RS485 converter.

However, with my converter, I see that

the PC software is receiving an echo of

whatever is being sent on the bus by it.

If I put a sniffer on the bus, I don’t

capture any echoes. So it seems like my

converter is generating an echo. Also, if

I run at higher baud rates, the data

received on the PC becomes more and

more incorrect. Could anybody tell me

what could be wrong?

Bruce Durdle replied:

I came across a similar problem a few

years ago, with an RS232-RS485

converter. The RS485 system was two-

wire, meaning the TX and RX lines

were paralleled. The “echoes” turned

out to be the system reading the

transmitted message as the response

from the slave. The problem was

solved by using CTS or RTS to disable

the receive part of the converter during

transmit.

An anonymous poster suggested:

Looks like a Frame Start/End problem

or Flow Control problem or silence

time problem between Modbus

messages or function asks and

responses. Check at http://

www.lammertbies.nl/comm/info/

modbus.html#tran.

From the Modbus Discussion Forum…

Muzammal Baig added:

If [the] RS485 line is too long and not

terminated you can get echoes. You

must terminate long RS485 lines with

120-Ohm resistors.

As you said, the commercial converter

works fine, so the fault doesn’t seem to

be in the line.

The higher baud rates causing more

problems means that the fault is in

hardware or the 485 programming.

Remember you must disable TX while

receiving and you must disable RX

while transmitting because 485 is a two-

wire half duplex protocol (not full-

duplex).

Conclusion:

1) Your microcontroller program is not

disabling RX while transmitting, which

is causing echo.

2) Your circuit does not have a

termination resistor or it is poorly

assembled so higher baud rates will get

corrupted.

Bob M. questioned:

Sounds simple, but perhaps you have

left the 485 transceiver “Receive

Enable” bit ON during transmit.

3. Pull the cable to the PLC#1.

4. At the PLC #1, terminate both black

and orange on the DATA+ terminal.

5. At the PLC#1, terminate both white

and red on the DATA- terminal.

6. At the terminal block, terminate one

end of a 4-conductor comm cable to

terminals 5 (black), 6 (white), 7 (orange)

and 8 (red).

7. At the PLC #2, terminate both black

and orange on the DATA+ terminal.

8. At the PLC#2, terminate both white

and red on the DATA- terminal.

9. At the terminal block, jumper 3 and

5, then 4 and 6.

10. At the terminal block, connect the

Modbus Master’s Data+ to terminal 1

and Data- to terminal # 2.

D. Parks cautioned:

RS485 optimally [can] be configured in

a daisy chain configuration, and at

worst in a trunk and spur configuration.

Using these configurations, depending

on your baud rate, it is possible to

extend the network up to 4000 ft.

I have experience trying to install a

Modbus RS485 network in a star

configuration. I can assure you if you

do this, it will cause you nothing but

trouble, and I highly recommend you

not attempt it. (The network which I

speak of is now a trunk and spur

design for this reason.)

There is probably a way to make a ring

configuration using fiber optic

converters, but this is probably more

trouble than it is worth.

Add your comments to this thread, at

modbus.control.com/1026235042.

RS485 Nodes in Star

Configuration...

In May Steven French wrote:

Could anyone tell me if it is acceptable

to connect multiple Modbus nodes in a

star configuration? Ideally I would use a

ring, but would like to take a single

power and single RS485 cable to each

junction box. Are there any

performance issues associated, and is

there a maximum drop length?

Tom Tran suggested:

You can run one cable to each PLC and

still maintain a ring network that is

compliant with RS485 standard. For

example, you have two PLCs:

1. Start with a terminal block.

2. Terminate one end of a 4-conductor

comm cable to terminals 1 (black), 2

(white), 3 (orange) and 4 (red).

Ask your question or help

out a fellow engineer on

the Modbus Discussion

Forum:

modbus.control.com

Modbus Products and Innovations

ProSoft Announces

New Industrial

Hotspot

ProSoft

Technology

announced the

addition of a

new 802.11abg

Industrial

Hotspot to its growing line of

RadioLinx products. The RLX-IHW

functions as a wireless access point,

repeater, or client and is designed for

global installations. It offers high-speed

wireless Ethernet communications

including EtherNet/IP, Modbus TCP,

and DNP over Ethernet for linking

automation systems, Ethernet I/O,

video cameras and plant network access

for mobile workers.

The RLXIHW uses OFDM

(Orthogonal Frequency Division

Multiplexing) for multi-path

interference rejection, RF multicast

packet filtering, and dual frequency

bands, which make it the ideal solution

for demanding, high-speed industrial

networks needing reliable performance.

Control Solution’s Newest Embedded

Server with 32 I/O Points, Modbus RTU

& Modbus TCP

Minnesota-based

Control Solutions,

Inc.,

announced the newest member

of its embedded server family, the

AddMe III model AM3-IP-MB. The

AM3-IP-MB includes 32 I/O points

plus a Modbus RTU port and Modbus

TCP in a full-featured web appliance.

The AM3-IP-MB includes time/date

and astronomical scheduling, data

logging and trending with log files

automatically e-mailed, event

notifications via e-mail, simple logic via

templates and complex logic via

programming language, SNMP agent,

and user-defined web page capability.

The server also supports dynamic DNS

and HTTP Get data logging.

The AM3-IP-MB is ideal for remote

monitoring and control applications,

because it includes I/O, control, and

web server features in a single DIN-rail

mounted box. Users can incorporate

dedicated controllers such as VFDs, or

additional slave I/O or PLCs to create

a larger system. Users can also

configure alarms and alarm responses,

change setpoints based on time/date,

perform scheduled control sequences,

or create their own HTML wrappers

around the provided web site to

customize the user interface.

For more information, contact Control

Solutions at 800-872-8613 or e-mail

sales@csimn.com. Visit the company’s

website, www.csimn.com, for complete

details including a guided tour and

demonstration of the AM3-IP-MB’s

embedded web site.

Advertise Your Modbus Products

on the Modbus-IDA Website

OFDM modulation provides excellent

noise immunity at maximum speeds.

This technique distributes data over

multiple carriers that are assigned

individual frequencies, so that each

carrier only sees its own, translating into

less distortion or interference.

ProSoft Technology wireless products

come with a three-year minimum

warranty and unlimited technical

support. For information call +1 661-

716-5100, e-mail prosoft@prosoft-

technology.com or visit www.prosoft-

technology.com.

With our growing number of site visitors and the increasing popularity of

our device directory, what better place to advertise your Modbus devices

and software than at www.modbus.org?

All banner ads must conform to the following specifications:

•

File size: 20k maximum

Maximum dimensions: 468 pixels x 68 pixels

File type: Graphics Interchange Format (GIF) or animated GIF

Resolution: 72 dpi

Color depth: 8 bit (256 colors)

Every banner must include a working URL.

controller.

Please note that we will not post ads. with cycle rates or animation modes

that are irritants to our visitors. We would be happy to help you design an

effective Web ad with acceptable cycle rates and types of animation.

Contact lenore@modbus-ida.org for a rate sheet.

Modbus Products and Innovations

SeaI/O Wireless - Solutions for What

Used to Be Impractical or Impossible

Earle Foster, VP Sales and Marketing

variety of applications including process

for

Sealevel Systems,

describes the

control, data acquisition, broadcast

new SeaI/O W-series as ideal for

automation, security, and facility man-

monitoring devices that are impractical

agement. They have an operating

or impossible to monitor with tradi-

temperature range from 0° to 70°C

tional cable solutions. That’s a primary

and optional extended range from -40°

advantage of the new wireless

to +85°C.

SeaI/O™ modules.

SeaI/O W-series Highlights

The SeaI/O W-

series is compatible

• Modbus TCP compliant

with industry

• 802.11b/g wireless networking standards

standards, commu-

• WEP, WPA-TKIP, and WPA2-AES encryption

nicating over

• Daisy chain up to 247 SeaI/O expansion

802.11b/g wireless

modules for abundant configuration possibilities

networks using

• Bundled with software configuration and

WEP, WPA-TKIP

diagnostic tools

and WPA2-AES

encryption stan-

dards.

SeaI/O W-series module prices start at

$589 and product is available immedi-

“The SeaI/O W-series opens a new set

ately from stock. All SeaI/O products

of really cool possibilities when com-

are covered by Sealevel’s lifetime

bined with other SeaI/O modules,”

Foster said with enthusiasm. “A SeaI/O warranty.

W-series module can be daisy chained

Sealevel Systems, founded in 1986,

with up to 247 SeaI/O expansion

provides industrial computing solutions

modules using convenient pass-through in addition to a variety of communica-

connectors. So you have this incredibly

tions and I/O products including PCI

expansive, versatile distributed control

Bus cards, Ethernet serial servers, USB

and monitoring network connected

serial adapters, PCMCIA cards, and

wirelessly to the host.

PC/104 modules.

All SeaI/O modules operate from 9-

The product line includes multi-port

30VDC, are powered by terminal

RS-232, RS-422/485, RS-232/422/485

block or DC jack, and are available

multi-interface high-speed sync/async,

with host connection options including

and digital/relay I/O.

Ethernet, USB, RS-485 and RS-232.

For more information, visit

www.sealevel.com.

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