Omega Products BD9-C2 Installation Manual

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User ’s Guide

BD9-C2, BD9-C4 (CN9 SERIES)

Communications option installation guide

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Introduction

The CN9 series controllers can all be ordered or
retrofitted with either an RS232 or RS485 serial
communications interface board. If the controller has the
communications interface fitted then skip to the section
titled Installation/Cabling.

Feature RS232 RS485

Type of transmission lines Unbalanced Differential
Maximum number of drivers 1 128
Maximum number of receivers 1 128
Maximum cable length 15m 1200m
Maximum data rate 19.2Kb/sec 19.2Kb/sec
Maximum CMV +/- 25V +12 to -7V

Table lists the features of both RS232 and RS485 standards.

Cable: To ensure data integrity over long transmission
distances, it is recommended that good quality RS485 cable
is used.

Recommended: RS485: Belden 9841, RS232: Belden 9501

2

FITTING A COMMUNICATIONS INTERFACE BOARD

The RS232 and RS485 interface boards are interchangeable
and are fitted in exactly the same way, please read the fitting
and safety instructions before proceeding.

Caution: Live circuits can hold charge for short

periods after isolation from the voltage supply.
Electrostatic precautions should be observed

when handling the controller outside the sleeve.

After isolating the controller from it’s supply, the controller
front bezel and circuit board assembly can be unplugged
from the sleeve. Grasp the bezel firmly by the recesses on
each side and pull. A screwdriver can be used as a lever if
required.

To fit the RS232 or RS485 interface you will require the
following parts, which are supplied with the interface.

Nylon Nut

Brass Nut

Nylon Bolt

Nylon Spacer

Insert the Nylon Bolt into the 3mm diameter hole
at the bottom left hand corner of the controllers
printed circuit board

Place spacer over Nylon bolt thread.

Screw the Nylon Nut onto the bolt.

Do not overtighten as this will damage the screw
thread.

Plug the 5-way female connector on the Comms
Board into the 5-way male connector on the
Controller board ensuring that connectors are all in
alignment. At the same time ensure the hole in the
Comms board fits over the screw thread.

Screw the Brass Nut onto the Comms board.
Do not overtighten but ensure it’s tight enough to
stop the board from moving.

Cut the top of the screw thread so that it is level
with the top of the Brass Half Nut.

3

Now you are ready to refit the Controller into
its case. To do this carefully slide the PCB into
the case aligning it with the connector arms
at the rear, and then press the bezel
assembly firmly into the sleeve until the latch
clicks in order to compress the gasket and
seal to NEMA4/IP66.

Diagram 1

RS485 CONNECTIONS

RS485 is a half duplex serial communications link and is the
standard most commonly used for industrial applications due
to it’s high noise immunity and multi-drop capability. It
enables a PC to communicate with up to 128 instruments
over distances up to 1200 metres, and requires the addition
of an RS485 interface card, or a separate RS232 / 485
converter.

Installation / Cabling

RS232 CONNECTIONS

RS232 is the standard most widely used for interfacing
peripherals to PC’s and is designed for serial communications
with single instrument up to distances of 15 metres, in a low
electrical noise environment.
Connection is via a screened two core cable where the
voltage signal on each line is referenced to the screen which
is grounded. Most PC’s have one or two RS232 compatible
ports fitted as standard.

4

1 2 3 4 5 6 7 8

9 10 11 12 13 14 15 16

rear terminal

1

5

69

PC Com Port

DB-9 Pin

Tx
Rx
Gnd

Tx Rx (+)

1 2 3 4 5 6 7 8

9 10 11 12 13 14 15 16

To

additional

units

1 2 3 4 5 6 7 8

9 10 11 12 13 14 15 16

unit 2

Tx Rx (-)

unit 1

Gnd

Tx Rx (+)
Tx Rx (-)
Gnd

Connections if PC 485 card used

To

RS 485

interface

Diagram 2 Diagram 3

Each RS485 interface has specific connection and
termination biasing requirements which will be
detailed in their installation instructions. The general
principals are as follows.

Terminations Because each wire is a transmission line,
it must be properly terminated to prevent reflections.
Where multiple instruments are daisy-chained
together, a 120 ohm terminating resistor should be
fitted at the connection to the PC and to the last
instrument in the chain.

Bias Resistors When transmission lines are not
transmitting, they remain in an indeterminate state
which can allow receivers to receive invalid data bits
due to electrical noise on the cable. To prevent this,
the lines should be forced into a known state by
fitting two 620 ohm bias resistors to one point
(node).

If an RS485 interface card is being fitted to the PC,
separate bias resistors may not be needed because
they may already be fitted to the card. Check the
manufacturers specification.

As mentioned earlier RS485 cards and converters
differ greatly in their requirements and therefore the
installation instructions supplied with the interface
should be read carefully.

5

–

Tx

Rx

+

+

–

+

–

+

–

Tx

Rx

+

–

+

–

Tx

Rx

+

–

+

–

Tx

Rx

Instrument 1 Instrument 2 Instrument ‘N’

+5V

620Ω

0V

620Ω

–

120Ω

Tx

Rx

+

+

–

+

–

+

–

Tx

Rx

+

–

+

–

Tx

Rx

+

–

+

–

Tx

Rx

120Ω

Instrument 1 Instrument 2 Instrument ‘N’

Diagram 4 Termination resistors

Diagram 5 Bias resistors

Immediately after power-up, both instrument, and PC comms
settings need to be made compatible before communication
between them is possible. Instrument defaults are shown
below together with available options.

(Address) This is a unique identification
number that must be allocated to each
instrument connected to the network.

Default = 0. Options;

1 to 247

(Baud rate) The setting determines the serial
communication data transmission rate in
bits/sec, and must match the PC settings.

Default = 9600.

Options;

1200; 2400; 4800; 9600 and 19200

NOTE: If a comms board has been retro fitted

the default baud rate is 1200.

(Data) Sets the transmission format,
and must match the PC settings

Data Format Table

Settings Start bits Data bits Parity Stop bits

Default 1 8 n (none) 1
Option 1 1 8 e (even) 1
Option 2 1 8 o (odd) 1

(Debug) Commissioning and
troubleshooting aid. Display shows when the
instrument is transmitting or receiving data by
rapidly flashing the three horizontal segments
of the first and last digit of the display.

First digit = Tx; last digit = Rx
Default = Off. Options;

off; on

Only use dbuG during commissioning or trouble-shooting
because it shares display segments and therefore corrupts
the normal display.

Instrument Comms Settings

6

!

ADDR

BAUD

DATA

DBUG

Configuring Instrument Comms Settings

This should also be done immediately after power-up, and
is only possible from the instrument front panel.

On power-up the controller will display the self test
sequence followed by Alternating INPT and

nonE

Note: During the following procedure the display will revert

to alternating INPT and

nonE

after 60 seconds of
keying inactivity, but will retain any settings already
completed. Should this occur, or in the event of becoming
‘lost’ in the program, please start again from the alternating

INPT and

nonE

display.

To select Level C (communications settings)
Press ▼ once display alternates LEVL and

5

Press and hold ✱ and press ▼ five times to reach level C

display alternates LEVL and

C

Note: Level C is only visible when the comms interface
board is fitted to the unit

To set instrument comms address
Press ▲ once display alternates ADDR and

0

Press and hold ✱ and press ▲ to index to chosen address

number

(1 to 247)

Note: In the absence of any conflicting information the

following comms settings should be left as the default values
(see details on page 6).

To read or adjust comms settings
Baud rate
Press ▲ once display alternates BAUD and

9600

(Default setting)
Press and hold ✱ and use ▲ or ▼ keys to select preferred

value.

Data format
Press ▲ once display alternates DATA and

18n1

(Default setting)
Press and hold ✱ and use ▲ or ▼ keys to select preferred

setting. (see table page 7).

Debug setting
Press ▲ once display alternates DBUG and

oFF

(Default setting)
Press and hold ✱ and use ▲ key to select

on

To enter settings into memory
Press and hold ▲ and ▼ for 3 seconds display alternates

INPT and

nonE

To check settings; repeat the above procedure
The unit is now ready to be configured from the PC.
Note: Where more than one instrument is connected to the

system, it is useful at this point to list them by location, title
and comms address. The list can then be used as a
reference to ensure that the instruments are given the same
identity when configuring the comms link from the PC.

!

7

Application Software

The controllers with the communications interface fitted use
the Modbus RTU protocol. If you wish to integrate the
controllers into a third party software application, or code
your own custom software application, there is a document
that explains how to communicate with the controllers. The
document is available from Omega

CN9-SW APPLICATION SOFTWARE

The easiest way to communicate with the controllers is using
the dedicated CN9-SW package for remote configuration and
data acquisition. This package requires no programming or
configuration and is ready to run, if you are familiar with
Windows applications you can be up and running in minutes.

CN9-SW PC REQUIREMENTS

To gain the full benefit of CN9-SW software, it is recommended
that the PC is fitted with a Pentium processor, running
Windows 95/98/ME/NT/2000 and has a graphics card capable of
displaying a minimum of 256 colours. A minimum of 16MB RAM
for Windows 95/98, 32Mb of RAM for Windows NT/ME or 64MB
of RAM for Windows 2000 is recommended, together with
enough free hard disk space to meet your logging requirements.

CN9-SW PERFORMANCE CONSIDERATIONS

When an application has more than 32 instruments on the bus,
we recommend you look at using a higher specification PC. If
you have between 32 and 128 instruments on the bus a
recommended minimum PC specification would be a Pentium

200MHz processor with 64Mb of RAM. To keep CPU and RAM
usage to a minimum it is generally good practice not to log
data more frequently than necessary, and also keep the time
base of charts as small as reasonably possible. If you need to
review the full chart history you should select ‘View Plot’ mode
and then increase the time base of the chart, remember to
return to ‘Auto Plot’ mode when finished. If possible you
should also increase the ‘Refresh Frequency’ option in the
‘Select Units To Chart’ screen. This option allows you to keep
logging data in the background, but only redraw the chart
when ‘X’ number of samples have been acquired from each
controller. For instance if the ‘Sample Frequency’ is set to 1
second and the ‘Refresh Frequency’ is set to 20, the chart will
only be redrawn and updated every 20 seconds, but logging
still continues in the background at the rate of once per
second.

Additional information
SETTING SECURITY LEVELS IN CN9-SW

It should be noted that functions that have been locked
appear to be still locked even when you are logged in at the
correct security level. This means that the operator or
supervisor have permission to unlock and adjust functions
they have locked, but have to unlock that function first, then
they can adjust the function. To retain your security settings
remember to re-lock any functions you have unlocked for
adjustment.

8

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