rotork Modbus IQ Pro User manual

Publication PUB091-003-00_0119
Modbus RTU Actuator Control
Mk2 Option Card
Technical Manual
(IQ Pro, IQT Pro, SI Pro, EH Pro, ROMpak and Q)

Modbus MFU Option Card Installation Manual
2 of 76 Publication PUB091-003-00_0119
The Modbus card described in this manual contains static-sensitive devices. Suitable
precautions, such as wearing an earthed anti-static wrist strap, should be taken before
handling the card. The card should be kept in an anti-static bag or box while it is not fitted
within an actuator.
Note 1: The Modbus Modules described in this manual are suitable for inclusion in Rotork IQ Pro, IQT
Pro, ROMpak, SI Pro, EH Pro and Q range actuators. The Modbus Modules may also be fitted to
earlier versions of the IQ range of actuators.
Note 2: Although the same Modbus module is fitted to the different ranges of actuators, there will be
different numbers of valid inputs and outputs for each range, depending on the actuator capabilities.
For example, actuators not fitted with a battery cannot report Battery Low.
Note 3: The information in this manual relates to the following Modbus module firmware release -
M207 or newer.
Note 4: Throughout this manual the Modbus Module may simply be referred to as the module or MFU
(Modbus Field Unit – the circuit board fitted to the actuator in the field).
Note 5: Inputs are the status messages from the actuator and outputs are the command messages to
the actuator.
As we are continually developing our products their design is subject to change without notice.
©The contents of this document are copyright and must not be reproduced without the written
permission of Rotork Controls Ltd.
The names Rotork and Modbus are registered trademarks.

Contents
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Contents
1INTRODUCTION .................................................................................................. 7
1.1 General ................................................................................................................................8
2MODBUS OPTION CARD PROPERTIES............................................................ 9
2.1 Mechanical properties ........................................................................................................9
2.2 Electrical Properties .........................................................................................................11
2.3 Operation and Storage......................................................................................................11
3FITTING THE MODBUS MODULE OPTION CARD .......................................... 12
3.1 Inside an IQ Pro or IQT Pro actuator................................................................................12
3.2 Inside a Q actuator............................................................................................................13
3.3 Inside ROMpak actuator ...................................................................................................14
3.4 Inside an SI or EH actuator...............................................................................................15
3.5 Replacing or Fitting a Modbus Module Option Card .......................................................16
4RS-485 DATA HIGHWAY, CONNECTIONS AND MFU SETUP........................ 17
4.1 Data Highway ....................................................................................................................17
4.2 Highway Topology ............................................................................................................18
4.3 Cable Types.......................................................................................................................19
4.4 Termination Network.........................................................................................................20
4.5 Inter-connecting the Highway and Setting up the MFU...................................................21
4.5.1 Single Highway with Analogue Input.............................................................................22
4.5.2 Dual Highway...............................................................................................................23
4.5.3 Single Highway with Internal Repeater .........................................................................24
5THE ACTUATOR INPUT AND OUTPUT SIGNALS .......................................... 27
5.1 Control Outputs ................................................................................................................27
5.1.1 Controls Priority ...........................................................................................................30
5.1.2 Modbus Control using Individual Coil commands..........................................................31
5.1.3 Modbus Control using the ACTCON Register ...............................................................31
5.1.4 Modbus Control using the Actuator Position DV register ...............................................31
5.1.5 The IQ ‘S’ contacts (Modbus DOs). ..............................................................................32
5.1.6 IQ Modbus Network Control Disable feature.................................................................32
5.2 Actuator Digital Input Status Feedback ...........................................................................32
5.2.1 Digital Inputs from All Actuator Types...........................................................................33
5.2.2 Digital Inputs from IQ and IQT Actuator ........................................................................36
5.2.3 Digital Inputs from IQT Actuator....................................................................................37
5.3 Actuator Analogue Input Feedback..................................................................................37
5.4 IQ Data Logger Information ..............................................................................................38
6MODBUS COMMUNICATION............................................................................ 40
6.1 Electrical Specification .....................................................................................................40
6.2 Outer Protocol...................................................................................................................40
6.3 Repeaters ..........................................................................................................................40
6.4 Dual Channel Mode...........................................................................................................41

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7MODBUS DATA BASE...................................................................................... 43
7.1 Modbus RTU Message Frame...........................................................................................43
7.2 Modbus Address...............................................................................................................43
7.3 Function Code Support ....................................................................................................44
7.4 Broadcast Commands ......................................................................................................46
7.5 Data Location Offsets .......................................................................................................46
7.6 Data Locations ..................................................................................................................46
7.6.1 Data Accessed with Function Code 01 - Read Coils .....................................................47
7.6.2 Data Accessed with Function Code 02 - Read Discrete Inputs......................................47
7.6.3 Data Accessed with Function Code 03 - Read Holding Registers..................................48
7.6.4 Data Accessed with Function Code 04 - Read Input Registers......................................50
7.6.5 Data Accessed with Function Code 05 and 15 – Force Single and Multiple Coils..........51
7.6.6 Data Accessed with Function Code 06 and 16 – Preset Single and Multiple Registers..51
7.6.7 Data Accessed with Function Code 07 – Read Exception Status ..................................52
7.6.8 Data Accessed with Function Code 08 – Loopback Diagnostic Test .............................52
7.6.9 Data Accessed with Function Code 17 – Report Slave ID.............................................52
7.7 Data Base Summary: ........................................................................................................53
8CONFIGURATION REGISTERS........................................................................ 55
8.1 Actuator Related Configurable Parameter Registers ......................................................57
8.1.1 Action on Loss of Communications (Register 7)............................................................57
8.1.2 Limited Range Position Minimum and Maximum (Registers 8 and 9) ............................57
8.1.3 Deadband and Hysteresis (Registers 10 and 14)..........................................................58
8.1.4 Motion Inhibit Timer (Register11)..................................................................................59
8.1.5 Auxiliary Input Mask (Register 12) ................................................................................59
8.1.6 Communications Lost Position (Register 13) ................................................................60
8.1.7 Slow Mode Range (Register 15)...................................................................................60
8.1.8 Valve Jammed Time (Register 16) ...............................................................................60
8.1.9 Manual Movement Travel (Register 17)........................................................................61
8.1.10 Watchdog Timeout (Register 18)..................................................................................61
8.1.11 ESD DI-4/Net Disable (Register 19)..............................................................................61
8.1.12 Analogue Input Max (Register 20) ................................................................................61
8.1.13 Communications Fault Timer (Register 21)...................................................................61
8.2 Modbus Network Related Configurable Parameter Registers ........................................61
8.2.1 Modbus Address (Register 22) .....................................................................................61
8.2.2 Baud Rate (Register 23)...............................................................................................62
8.2.3 Parity and Stop Bits (Register 24).................................................................................62
8.2.4 Data Base Format (Register 25)...................................................................................62
8.2.5 Actuator Tag Name (Register 26 to 31) ........................................................................62
8.3 Return to Defaults.............................................................................................................62
9SETTING UP AND MAINTAINING THE MODBUS MODULE ........................... 63
9.1 Using a Network Configuration Tool................................................................................63
9.2 Setting up an IQ or IQT with the Setting Tool ..................................................................63
10 MAINTENANCE AND REPAIR ....................................................................... 66
10.1 Records..........................................................................................................................66
11 TROUBLESHOOTING .................................................................................... 67
12 APPENDIX A – MODBUS MODULE MK1 DATA BASE ................................ 69

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12.1 Introduction ...................................................................................................................69
12.2 Input and Output Signals ..............................................................................................69
12.2.1 Control Outputs............................................................................................................69
12.2.2 Digital Input Status Feedback.......................................................................................70
12.2.3 Analogue Input Status Feedback..................................................................................70
12.3 Modbus Communication ...............................................................................................71
12.4 Modbus Data Base.........................................................................................................71
12.4.1 Function Code Support ................................................................................................71
12.4.2 Broadcast Messages....................................................................................................71
12.4.3 Data Locations.............................................................................................................72
12.5 Configuration.................................................................................................................75
12.6 Records..........................................................................................................................75
Table of Figures
Fig 1: The Modbus Module Option Card Actuator Compatibility....................................................7
Fig 2: The Types of Modbus Module Mk2 Option Card ................................................................8
Fig 3: The Modbus single channel NIC, showing the network connector. .....................................9
Fig 5: The Interface Card (SI Pro and EH Pro actuators, Q is similar, see Section 3.2)...............10
Fig 6: The Interface Card (IQ Pro and IQT Pro actuators) ..........................................................10
Fig 8: The MFU module profiled for the Q actuator ....................................................................13
Fig 9: The MFU located in a ROMpak actuator ..........................................................................14
Fig 11: Typical RS-485 Data Highway .........................................................................................17
Fig 12: RS-485 Data Highway Topology......................................................................................18
Fig 13: Typical RS-485 cable.......................................................................................................19
Fig 14: Termination for RS-485 highway......................................................................................20
Fig 15: Termination for RS-485 highway in ROMpak actuators. The links are shown in the non-
terminated position. .........................................................................................................21
Fig 16: Single Highway + Analogue Input Connections ................................................................22
Fig 18: Jumper Settings for Dual Highway Option........................................................................23
Fig 17: Dual Highway Connections..............................................................................................23
Fig 19: Single Highway with Internal Repeater Connections.........................................................25
Fig 20: Jumper Settings for Single Highway with Internal Repeater Option...................................26
Fig 21: Input and Output Data Direction.......................................................................................27
Fig 24: IQ and IQT relay outputs DO-1 to DO-4 ...........................................................................32
Fig 25: Modbus transaction format...............................................................................................43
Fig 26: Limited Range Position Control and Reporting.................................................................57
Fig 27: Deadband and Hysteresis settings...................................................................................58
Fig 28: Setting tool menu structure and MFU settable parameters ...............................................64

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Glossary of Terms:
Address The unique address for a node on the fieldbus, range 1-247.
Fieldbus The digital, two-way, multi-drop communication links.
Field Unit The Modbus option card fitted to the actuator
Master/Slave The method of communication used by the Modbus Module. The
fieldbus requires a Modbus master to control the data exchange on
the highway.
Modbus The communication protocol used for data exchange.
Modbus RTU The version of the protocol available from the Rotork module.
Node A single device on the fieldbus.
RS-485 The electrical properties of the data highway as defined by the IEC
standard, copper conductors, 2 wire twisted pair.
Segment A section of an RS-485 fieldbus that is terminated in its characteristic
impedance. Each Segment can include up to 32 devices.
Abbreviations:
ACTCON Actuator Control (Register).
CRC Cyclic Redundancy Check (error detection).
DV Desired Value.
ESD Emergency Shut Down.
IEC International Electrotechnical Commission.
MFU Modbus Field Unit.
MV Measured Value.
NIC Network Interface Card.
PCB Printed Circuit Board.
PLC Programmable Logic Controller.
RAM Random Access Memory.
ROM Read Only Memory.
RTU Remote Terminal Unit.
SIL Safety Integrity Level
SW Software.

Introduction
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1 INTRODUCTION
The Rotork Modbus Module Actuator Control option card (MFU) uses 2-wire (half-duplex) RS-485 and
the Modbus RTU protocol to allow for information exchange and control over the data highway
between the actuator and a suitable host system with a Modbus capability.
The module is an integral part of the actuator in which it is housed and is fitted within the main
electrical housing. For the IQ Pro, IQT Pro, SI Pro, EH Pro and Q products this electrical housing is
double sealed and need never be opened once the actuator leaves the assembly plant. The ROMpak
actuators do not have double sealing and the electrical cover is required to be entered for connecting
to the Field connections.
All adjustments to the settings for the module may be made via the Modbus data highway using a
Modbus master tool or via the Infra-red setting tools for the IQ Pro, IQT Pro, SI Pro and EH Pro
products. (If the data highway speed was not specified at time of order, or it is changed, it may be
necessary to change the links on a Single Highway plus Repeater option, see Section 4.5.3.)
The Modbus Module circuits do not impinge on the actuator control electronics; the actuator itself
remains fully self-protecting. The module performs the tasks of network interface, actuator data
collection and the issuing of actuator commands.
The Modbus Module may command the actuator into which it is fitted to open, stop, close, perform an
ESD operation or move to a set position. Commands to the module come from the network and will
have been generated in a master controller. The module operates in Master/Slave communication
mode only using Modbus RTU protocol. For SI and EH actuators, where a SIL approved safety
function is required, the hard wired ESD control should be used and not the Modbus ESD function.
Fig 1: The Modbus Module Option Card Actuator Compatibility

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1.1 General
The Modbus Module has three variants:
Single RS-485 highway plus one analogue input channel
Dual Independent isolated RS-485 highways
Single RS-485 highway with inbuilt isolating repeater
Communication Medium RS4-85 2-wire highway (single or dual), half duplex
Protocol Modbus RTU
Mode Master/Slave, module is a slave
Fig 2: The Types of Modbus Module Mk2 Option Card
RS485
Highway
Analogue
Input
Single Highway + Analogue Input
Dual Highway
Single Highway + Repeater
RS485
Highway 1
RS485
Highway 2
RS485
Highway 1
RS485
Highway 1

MFU Properties
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2 MODBUS OPTION CARD PROPERTIES
2.1 Mechanical properties
The MFU module consists of a network interface card, that either fits directly to the main actuator
printed circuit board (ROMpak) or fits to an interface card; where the two board assembly is then fitted
inside the actuator electrical housing (IQ Pro, IQT Pro, SI Pro, EH Pro and Q).
All the connectors are polarised to prevent incorrect insertion.
Network Interface Card (NIC)
This small printed circuit board carries the Modbus, RS-485 highway connections and protection
circuits. There are two versions of the Network Interface Card, one for a single highway and a
second for two highway (or one highway with repeater) use.
Fig 3: The Modbus single channel NIC, showing the network connector.
Fig 4: The Modbus dual channel NIC.
Network Connector
Network Connector

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Interface Card (IQ Pro, IQT Pro, SI Pro, EH Pro and Q)
The ROMpak does not require an additional interface card.
The interface card is profiled and assembled to fit an IQ Pro, IQT Pro, SI Pro, EH Pro or Q
actuator. For the SI Pro, EH pro and Q, it carries the processor for collecting the data from the
actuator main board and passing this data to the Network Interface card. For the IQ Pro and
IQT Pro it is used simply for physical connection to the main card.
The primary connection to the actuator circuits is by a multi-pin connector on the Interface Card
that, due to its physical shape may only be fitted in the correct polarisation. Internal wiring
harnesses connect to the Interface card for other signals and options within the actuator. The
Interface card is powered from within the actuator.
Fig 5: The Interface Card (SI Pro and EH Pro actuators, Q is similar, see Section 3.2)
Fig 6: The Interface Card (IQ Pro and IQT Pro actuators)

Contents
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Early assemblies of NIC and Interface Cards were physically joined by their electrical connectors and
a push-fit spacing pillar. Later versions use a threaded pillar, which is useful for higher vibration
environments.
2.2 Electrical Properties
The MFU connects directly to the Interface Card of the actuator. The MFU does not sit in the main
control path for the actuator and does not affect the actuator control integrity.
The Modbus RS-485 fieldbus data highway connections are fully isolated from the actuator
electronics.
2.3 Operation and Storage
The MFU is designed to be stored in the actuator and operated within the same environment as the
actuator. The constraints are:
Operating temperature: -40degC to +70degC
Storage temperature: -50degC to +85deg C
Relative Humidity: 5% to 95% (<50degC) non-condensing

RS-485 Data Highway, Connections and MFU Setup
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3 FITTING THE MODBUS MODULE OPTION CARD
3.1 Inside an IQ Pro or IQT Pro actuator
The MFU is suitable for fitting into IQ Pro actuators with 3000 or 5000 series wiring diagrams and IQT
Pro with 6000 or 7000 series wiring diagrams. The connections and fitting in an IQT Pro is similar to
that for an IQ Pro and the following information effectively relates to both actuator types. The MFU is
normally located in the first option board slot inside the electrical housing using connection SK1 to the
Main pcb.
Fig 7: The IQ Pro and IQT Pro MFU and its location in an IQ Pro or IQT Pro actuator
With the IQ Pro and IQT Pro actuators the remote inputs are always present (they are conditioned by
the MFU) and there is an option to include Digital Outputs from relay contacts. If the MFU is required
to operate the 4 digital outputs that can be controlled from the card then the Extra Relay Indication
card associated with these outputs must be fitted into the actuator. The following table describes the
wiring harnesses and their function in the IQ and IQT actuator.
MFU Socket Wiring Harness
SK2 24V power supply input from actuator
SK3 Modbus RS-485 Fieldbus connection
SK10 Analogue Input connection 
Note: Only available on Single Channel module, wiring diagram 3000-400 or 6000-400
.
LK1

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3.2 Inside a Q actuator
The MFU is fitted in the option board position in this actuator. Only one option board may be fitted at
any one time. The necessary internal components must also be present; in this case a potentiometer
and auxiliary limit switches at end of travel must be fitted to the actuator.
The illustration (Fig 8) shows the Q version of the circuit board.
Digital Outputs from relay contacts are not supported from the Q actuator, nor is the ability to report
the status of the remote control inputs as Digital Inputs. The following table shows the wiring
harnesses that must be fitted and the function of each loom for the Q range actuator.
MFU Socket Wiring Harness
SK2 24V power supply input from actuator
SK3 Modbus RS-485 Fieldbus connection
SK9 Limit switches
SK10 Analogue Input connection 
SK11 Potentiometer
Note: - Only available on Single Channel module
In a Q actuator there is a direct connection from PL2 on the Modbus Module to SK5 of the actuator
main board.
To restore the card to its default of Modbus Mk2 and the associated default parameter settings, LK1
should be fitted and the actuator power cycled. In normal operation LK1, shown above in Figure 8,
should not be fitted.
Fig 8: The MFU module profiled for the Q actuator
SK10
EPROM
SK9 SK11
SK2
LK1
SK3

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3.3 Inside ROMpak actuator
The MFU is suitable for fitting into ROMpak actuators, wiring diagram RX0X-4X0 (where X can be any
value) details the option card connections on the terminal strip. The MFU module is fitted in the only
option board slot inside the ROMpak electrical housing.
Fig 9: The MFU located in a ROMpak actuator
SK3 is the connection to the Modbus Fieldbus Data Highway; this is connected to SK23 on the main
PCB assembly via an internal loom. The user wires the Modbus connections to the main PCB
assembly at the terminal block SK18 as per the wiring diagram.
The MFU card fitted in the ROMpak actuator cannot be defaulted by the LK1 method previously
described for the Q actuator, as there is no interface card fitted between the MFU card and the
actuator Main PCB.

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3.4 Inside an SI or EH actuator
The MFU is suitable for fitting into SI Pro and EH Pro actuators, wiring diagram SWM SI-001. The
MFU is normally located in the first option board slot inside the electrical housing using connection
SK1 to the Main pcb.
Fig 10: The MFU and its location in an SI Pro or EH Pro actuator
With the SI Pro and EH Pro actuators the remote inputs are always present (they are conditioned by
the MFU) and there is an option to include Digital Outputs from relay contacts.
The following table describes the wiring harnesses and their function in the SI Pro and EH Pro
actuators.
MFU Socket Wiring Harness
SK 2 24V power supply input from actuator
SK 3
SK 10
Modbus RS-485 Fieldbus connection
Analogue Input connection 
Note: - Only available on Single Channel module
LK1

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3.5 Replacing or Fitting a Modbus Module Option Card
The MFU should be replaced or fitted only in a suitable environment. The actuator must be made
electrically safe before opening any covers.
The Modbus card described in this manual contains static-sensitive devices. Suitable
precautions, such as wearing an earthed anti-static wrist strap, should be taken before
handling the card. The card should be kept in an anti-static bag or box while it is not fitted
within an actuator
The electrical housing cover should be removed and the existing MFU carefully unplugged from its
main connector. Once removed from the main connector, the wiring loom connectors should be
removed. The replacement board is fitted in the reverse order to removal. The wiring harnesses are
polarised so that only the correct one will fit its mating part on the circuit board.
If the operation is to fit an MFU for the first time then the necessary wiring looms must be added to the
internal wiring harness of the actuator. The actuator wiring diagram shows the connectors and
harnesses used. The wiring harnesses are fitted inside the actuator before attempting to fit the MFU.
Once the looms are in place connect them to the MFU, then fit the MFU to the actuator main board
connector.
Once the module is fitted, the actuator should be re-assembled.
Once power is applied the field unit parameters should be checked and corrected where necessary,
see Section 9.

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4 RS-485 DATA HIGHWAY, CONNECTIONS AND MFU SETUP
4.1 Data Highway
The MFU uses RS-485, 2-wire, half duplex, Modbus RTU communications at various data rates. The
rules governing the installation and connection of an RS-485 highway should be observed at all times
to produce a successful installation. The RS-485 highway does not allow power to be transferred and
the MFU is powered from the actuator itself. The MFU can only report data when the actuator is
powered up.
Fig 11: Typical RS-485 Data Highway
The data highway must be terminated with a proper termination resistor at each end. The highway
itself can use tapped spur or stub connections to the actuators but it is recommended to keep any stub
lengths to a minimum for successful operation. Alternatively, the connection can be made in and out of
each actuator in a daisy chain arrangement. The length of the highway and number of devices
connected will vary from project to project. The standard permits up to 32 devices to be connected on
a section, though one of these will be the PLC. If more devices are needed (up to the maximum
addressable of 247) then RS-485 repeaters may be added after each group of 32. The standard
default address used by the Modbus Module is 247.
The length of the highway will determine the maximum speed for the data transmission. The greater
transmission speeds are obtained at the lower lengths.
Although RS-485 requires only 2 wires for data transmission the standard also requires that all the
nodes on the network have a maximum common mode differential of +7 volts. This requires the
ground potential at all points to be within the 7 volt limit. If the equipment is distributed over a wide
area, or an area with poor ground conductivity, it may be necessary to connect a third wire between all
the nodes. Most successful installations use 3 wires and Rotork provides a ‘common’ terminal on the
actuator.
Since the data passes over a single 2 wire cable there are periods between messages when no
devices are actively driving the lines. In order to ensure that data continues to flow correctly after
these periods it is advisable to ensure the lines are biased to suitable voltage levels during the time
the line is idle. This is usually achieved by biasing at the PLC. The MFU contains internal biasing
circuits that ensure suitable levels are maintained on the line even with no device transmitting.
Terminator
T
2 wire highway Screened cable
PLC
T

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4.2 Highway Topology
Two different connection topologies can be used for RS-485. The first system is to use a trunk line
with various spurs or drop lines from it. This system will require the location of the taps in junction
boxes near to the actuators. With the second the actuators can be directly connected to the trunk line
in a daisy chain. All the configurations require the cumulative total of the drop lines and stub lines to
be kept within the permitted maximum for the network speed to be used.
It is good practice to avoid spurs wherever possible.
Fig 12: RS-485 Data Highway Topology
The maximum Trunk length and that for each spur and the cumulative total are dependent on the
system speed in use. The table below suggests the maximum figures for cable type A, also defined
below. The segment length is the total of the trunk and all the spurs added together.
Data Rate (Baud) Maximum
Segment Length
Total Spur
Length
300 24.0 km 2.0 km
600 12.0 km 1.0 km
1k2 12.0 km
1.0 km
2k4 6.0 km
500 metres
4k8 3.0 km
500 metres
9k6 1.5 km
500 metres
19k2 1.2 km 500 metres
38k4 1.0 km 300 metres
57k6 750 metres 200 metres
115k2 500 metres 100 metres
(Note that each actuator includes up to 0.6 metres of Drop length)
Actuator Type IQ / IQT SI / EH ROMpak / Q
Internal Drop length (metres) 0.6 0.6 0.3
Within each actuator there is a short drop line or stub connection wire from the terminals to the MFU
itself. This length must be included in any calculation for total and individual drop lengths.
PLC
T
TapTap Tap Tap Tap
PLC
T
Spur
Trunk Cable
Trunk Cable
T
T

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4.3 Cable Types
The network must be connected using a suitable cable. Two conductors plus a shield and drain wire
are required as a minimum, though Rotork recommends the use of a 3 wire cable to ensure the
common mode voltage between all the actuators and the PLC is kept within the RS-485 specified
limits.
Amongst the cable manufacturers Belden have the PVC jacketed 3105A single pair 2 core cable,
which meets the minimum requirement. Belden 3106A has an extra core and therefore has sufficient
conductors to include a common wire between all the nodes on the network and meets the Rotork
recommendation. Information on Belden cable may be found on the Belden web site
(www.belden.com) or at http://bwcecom.belden.com/, where a search on RS-485 will reveal technical
papers and cable information.
Belden Part No.
Total Number of
Conductors
AWG
(stranding)
dia. Inches
Nom. DCR Insulation material
Nominal
O.D.
Nom
Impedance
(ohms)
Nominal
Capacitan
ce
3105A
Paired -
EIA Industrial
RS-485 PLTC/CM
2
22 AWG
(7 x 30) 48.2 ohm/km
Overall PVC jacket
Datalene insulated
twisted pair
7.26 mm 120 11.0 pF/ft.
3106A
Composite - EIA
Industrial RS-485
PLTC/CM
3
22 AWG
(7 x 30) 48.2 ohm/km
Overall PVC jacket
Datalene insulated
twisted pair
7.67 mm 120 11.0 pF/ft.
Fig 13: Typical RS-485 cable
The terminals to which the wires connect in the each actuator type will be different and the actuator
wiring diagram must be consulted to establish the connections.
Data Pair
Screen
Belden 3105A Belden 3106A
Common
Data Pair
Screen

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4.4 Termination Network
In order to operate correctly all RS-485 highways must be terminated at each end of the main trunk
line using a suitable resistor (120 ohms nominal). These will usually be near the scanner PLC and
near the furthest actuator. The resistors are connected between data line A and data line B. If the
termination resistors are not fitted there is a possibility that the network communications will be
unsatisfactory. In some cases network data line biasing may also be necessary, however to minimise
this requirement the actuator transceiver chips include secure turn round components.
For IQ / IQT, SI / EH and Q actuators that use the MFU, there is a termination resistor inside each
actuator. One side of the resistor is brought to a terminal whilst the other is already connected to data
line A. Linking the Terminator terminal to data line B completes the connection to place the resistor
across the data lines.
Fig 14: Termination for RS-485 highway
RS485
Highway
Analogue
Input
120 ohm
Data 1B
Data 1A
Terminator
Single Highway + Analogue Input
Dual Highway
Single Highway + Repeater
RS485
Highway 1
RS485
Highway 2
RS485
Highway 1
RS485
Highway 1
120 ohm
Data 1B
Data 1A
Terminator
120 ohm
Data 2B
Data 2A
Terminator
120 ohm
Data 1B
Data 1A
Terminator
120 ohm
Data 1B
Data 1A
Terminator