rotork Modbus Technical Manual

Publication PUB091-004-00_0918

Modbus RTU Actuator Control

Mk 3 Option Card

Technical Manual

(IQ3, SI3, CVA, CMA, K-Range)

Modbus MFU Option Card Installation Manual

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The Modbus card described in this manual has been designed to fully comply with Modbus protocol specifications. This means that network biasing must be used somewhere on the highway to ensure good communications. See Section 4.

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. It 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 IQ3, SI₃, CVA (Only firmware version CVA1.14 or later), CMA and K-range 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 version: V0050 or later.

Note 4: Throughout this manual the Modbus Module may simply be referred to as the module, card 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.

permission of Rotork Controls Ltd. The names Allen, Bluetooth, Modbus, Rotork and Torx are registered trademarks.

Contents

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Contents

Glossary of Terms: ............................................................................................................................ 5

Abbreviations: .................................................................................................................................... 6

1 INTRODUCTION ............................................................................................ 7

1.1 General ..................................................................................................................................... 8

2 MODBUS OPTION CARD PROPERTIES ...................................................... 9

2.1 Mechanical properties ............................................................................................................ 9

2.2 Electrical Properties ............................................................................................................. 10

2.3 Operation and Storage ......................................................................................................... 10

3 Fitting the Modbus module Option Card .................................................. 11

3.1 Inside an IQ3 actuator .......................................................................................................... 11

3.2 Replacing or Fitting a Modbus Module Option Card ......................................................... 11

3.3 Inside an SI₃ actuator ............................................................................................................ 12

3.4 Inside a CVA actuator ........................................................................................................... 13

3.5 Inside a CMA actuator .......................................................................................................... 14

3.6 Inside a K-Range actuator .................................................................................................... 18

4 RS-485 Data Highway, Connections and MFU Setup .............................. 19

4.1 Data Highway ......................................................................................................................... 19

4.2 Highway Topology ................................................................................................................ 20

4.3 Cable Types ........................................................................................................................... 21

4.4 Termination Network ............................................................................................................ 22

4.5 Inter-connecting the Highway and Setting up the MFU .................................................... 23

4.5.1 Single Highway ................................................................................................................ 23

4.5.2 Dual Highway ................................................................................................................... 23

4.5.3 Single Highway with Internal Repeater ............................................................................ 24

5 The Actuator Input and Output Signals .................................................... 25

5.1 Control Outputs ..................................................................................................................... 25

5.1.1 Controls Priority ............................................................................................................... 29

5.1.2 Modbus Control using Individual Coil commands............................................................ 29

5.1.3 Modbus Control using the ACTCON Register ................................................................. 30

5.1.4 Modbus Control using the Actuator Position DV register ................................................ 30

5.1.5 The IQ3 ‘S’ contacts (Modbus DOs). ............................................................................... 30

5.1.6 IQ3 Modbus Network Control Disable feature ................................................................. 31

5.2 Actuator Digital Input Status Feedback .............................................................................. 31

5.2.1 Digital Inputs from the Actuator ....................................................................................... 32

5.3 Actuator Analogue Input Feedback .................................................................................... 36

5.4 IQ3 Data Logger Information ............................................................................................... 36

6 Modbus Communication ............................................................................ 39

6.1 Electrical Specification ......................................................................................................... 39

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6.2 Outer Protocol ....................................................................................................................... 39

6.3 Repeaters ............................................................................................................................... 39

6.4 Dual Channel Mode ............................................................................................................... 40

7 Modbus Database ....................................................................................... 41

7.1 Modbus RTU Message Frame .............................................................................................. 41

7.2 Modbus Address ................................................................................................................... 41

7.3 Function Code Support ........................................................................................................ 42

7.4 Broadcast Commands .......................................................................................................... 44

7.5 Data Location Offsets ........................................................................................................... 44

7.6 Data Locations ...................................................................................................................... 44

7.6.1 Data Accessed with Function Code 01 - Read Coils ....................................................... 44

7.6.2 Data Accessed with Function Code 02 - Read Discrete Inputs ....................................... 45

7.6.3 Data Accessed with Function Code 03 - Read Holding Registers .................................. 46

7.6.4 Data Accessed with Function Code 04 - Read Input Registers ...................................... 48

7.6.5 Data Accessed with Function Code 05 and 15 – Force Single and Multiple Coils .......... 49

7.6.6 Data Accessed with Function Code 06 and 16 – Preset Single and Multiple Registers . 49

7.6.7 Data Accessed with Function Code 07 – Read Exception Status ................................... 49

7.6.8 Data Accessed with Function Code 08 – Loopback Diagnostic Test .............................. 50

7.6.9 Data Accessed with Function Code 17 – Report Slave ID .............................................. 50

7.7 Database Summary:.............................................................................................................. 51

7.8 Configuration Registers ....................................................................................................... 53

7.9 Actuator Related Configurable Parameter Registers ........................................................ 54

7.9.1 Action on Loss of Comms (Register 7) ............................................................................ 55

7.9.2 Limited Range Position Minimum and Maximum (Registers 8 and 9) ............................. 55

7.9.3 Deadband and Hysteresis (Registers 10 and 14)............................................................ 55

7.9.4 Motion Inhibit Timer (MIT) (Register 11) .......................................................................... 57

7.9.5 Auxiliary Input Mask (Register 12) ................................................................................... 57

7.9.6 Comms Lost Position (Register 13) ................................................................................. 58

7.9.7 ESD DI-4/Net Disable (Register 19) ................................................................................ 58

7.9.8 Analogue Input Max/Min (Register 20) ............................................................................ 58

7.9.9 Comms Fault Timer (Register 21) ................................................................................... 58

7.10 Modbus Network Related Configurable Parameter Registers ...................................... 59

7.10.1 Modbus Address (Register 22) ........................................................................................ 59

7.10.2 Baud Rate (Register 23) .................................................................................................. 59

7.10.3 Parity and Stop Bits (Register 24) ................................................................................... 59

7.10.4 Termination (Register 25) ................................................................................................ 59

7.10.5 Actuator Tag Name (Register 26 to 31) ........................................................................... 59

8 Setting Up and Maintaining the MFU ........................................................ 61

8.1 Using a Network Configuration Tool ................................................................................... 61

8.2 Setting up an IQ3 with the Setting Tool .............................................................................. 61

8.3 Maintenance and Repair ....................................................................................................... 62

8.4 Records .................................................................................................................................. 62

8.5 Troubleshooting .................................................................................................................... 63

Contents

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Table of Figures

Fig 1: The Modbus Module Option Card Actuator Compatibility ..................................................... 7

Fig 2: The Modbus Field Unit .......................................................................................................... 9

Fig 3: The MFU and its location behind the control module in an IQ3 .......................................... 11

Fig 4: The MFU located on the underside of the control PCB in a CVA actuator ......................... 13

Fig 5: The MFU located in a CMA actuator ................................................................................... 14

Fig 6: CMA menu structure for setting up the actuator: start at the BASIC setting ....................... 15

Fig 7: CMA menu structure for setting up the actuator: from the ADVANC setting, ..................... 16

Fig 8: CMA menu structure for setting up the actuator: from the COMMS setting,....................... 17

Fig 9: Connections to the MFU located in a CMA actuator ........................................................... 17

Fig 10: The MFU located in a K-Range actuator ............................................................................. 18

Fig 11: Typical RS-485 Data Highway ............................................................................................ 19

Fig 12: RS-485 Data Highway Topology ......................................................................................... 20

Fig 13: Typical RS-485 cable .......................................................................................................... 21

Fig 14: Active Termination for RS-485 highway. Biasing resistor values are typical. ..................... 22

Fig 15: Input and Output Data Direction .......................................................................................... 25

Fig 16: IQ3 Control Priorities ........................................................................................................... 29

Fig 17: Modbus transaction format .................................................................................................. 41

Fig 18: Limited Range Position Control and Reporting ................................................................... 55

Fig 19: Deadband and Hysteresis settings...................................................................................... 56

Glossary of Terms:

Address The unique address for a node on a particular highway of the fieldbus.

The address range is 1-247.

Enlight A graphical user interface for Bluetooth communication with CVA

actuators. This is downloadable from the Rotork web site,

www.rotork.com Fieldbus The digital, two-way, multi-drop communication links. Field Unit The Modbus Mk 3 option card fitted to the actuator. Insight2 A graphical user interface for communication with IQ3, SI3 and CVA

actuators. This is downloadable from the Rotork web site,

www.rotork.com Interoperability The capability for a device from one manufacturer to interact with that

of another manufacturer, on a fieldbus network, without loss of

functionality. Master/Slave 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, as defined in

IEC 61850. Modbus RTU The version of the protocol used by the Rotork module. Node A single device on the fieldbus. Parity Bit added to data for error detection.

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Partial Stroke Test Moving a little-used valve by a small percentage from an end limit and

then returning it, proving that it will operate when required. Safety

related. RS-485 The electrical properties of the data highway as defined by the IEC

8482 standard, copper conductors, 2-wire twisted pair. Segment A section of an RS-485 fieldbus that is terminated at each end in its

characteristic impedance. Each Segment can include up to 32 devices

with unitary load.

Abbreviations:

ACTCON Actuator Control (Register). CMA Compact Modulating Actuator. Comms Communications. CRC Cyclic Redundancy Check (error detection). CVA Control Valve Actuator. CVL Linear version of CVA. CVQ Quarter-turn version of CVA. DIO 1 Digital Input / Output Board, type 1. DIO 2 Digital Input / Output Board, type 2. DV Desired Value. ESD Emergency Shut Down. IEC International Electrotechnical Commission. MFU Modbus Field Unit. MV Measured Value. PCB Printed Circuit Board. PLC Programmable Logic Controller. RAM Random Access Memory. RIRO 1 Remote Input / Remote Output Board, Type 1. RIRO 2 Remote Input / Remote Output Board, Type 2. ROM Read Only Memory. RTU Remote Terminal Unit. SW Software. UPS Uninterruptible Power Supply (CVA only).

Introduction

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1 INTRODUCTION

The Rotork Modbus Module Actuator Field Control option card (MFU) uses 2-wire (half duplex) RS485 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 IQ3, CVA and K-Range products, this electrical housing is double-sealed and need not be opened once the actuator leaves the assembly plant. The CMA range of actuators does not have double sealing and the electrical cover is required to be opened for connecting to 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 or Bluetooth actuator setting tools for those products that support those interfaces.

The settings which must be correct for communication are: address, baud rate, parity and stop bits. These are described in Section 6. The default values are: address 247, baud rate 9600, parity None and stop bits 1.

The Modbus Module circuits do not impinge on the actuator control electronics; the actuator itself remaining 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, perform a partial stroke test (IQ3 only) 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 as a slave in Master/Slave communication mode only, using the Modbus RTU protocol.

Fig 1: The Modbus Module Option Card Actuator Compatibility

IQ3

CVA

K-Range

CMA

SI3

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1.1 General

The Modbus Module has three variants:

 Single RS-485 highway  Dual Independent isolated RS-485 highways  Single RS-485 highway with inbuilt isolating repeater

Communication Medium RS-485 2-wire highway (single or dual), half duplex Protocol Modbus RTU Mode Master/Slave; module is a slave.

Modbus Option Card Properties

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2 MODBUS OPTION CARD PROPERTIES

2.1 Mechanical properties

The Modbus module option card differs from all previous versions in that it interfaces directly between the Modbus RTU network and the communication protocol used within the actuator. There is no intermediate circuit board that it plugs into. We refer to it as the Modbus Field Unit, MFU.

The MFU is a single rectangular printed circuit board that fits inside the actuator electrical housing. It connects directly to the Control Module PCB of the actuator by a ten pin connector (10 way header, SK2). The field unit should be carefully fitted so that the connectors mate correctly. The actuator internal wiring harness connects the field unit at SK3 to the Modbus highway via the actuator terminal bung. The connector is polarised to prevent incorrect connection.

In the IQ3, the field unit can be fitted directly to the Control Module PCB using either one of the 2 slots available, or can be fitted on top of another option module that may already be fitted in one of these slots. There are 4 available slots for option cards to be mounted either directly or indirectly behind the Control Module PCB.

Fig 2: The Modbus Field Unit

SK3 – Field connections.

Control board connection. SK2 connector fitted on underside of MFU.

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2.2 Electrical Properties

The MFU processor circuits communicate to other modules in the actuator via an internal communications bus. The MFU does not sit in the main control path for the actuator and does not affect the actuator control integrity. The MFU processor contains the firmware for the unit. The firmware version is indicated on the label fitted to the processor. It can also be read from the actuator using the setting tool, by using Insight with Infra-red or by using Insight2 with Bluetooth, where appropriate.

Additionally, the circuit includes non-volatile memory that is used to store specific field unit communications settings.

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: -40deg C to +70deg C  Storage temperature: -50deg C to +85deg C  Relative Humidity: 5% to 95% (<50deg C) non-condensing

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3 FITTING THE MODBUS MODULE OPTION CARD

3.1 Inside an IQ3 actuator

The MFU is suitable for fitting into IQ3 actuators. When factory-fitted, their wiring diagrams will contain an ‘M’ - 100M2000 for single channel and 100M3000 for dual channel. The MFU can be located in one of 2 or 4 option ‘slots’ located on the back of the control module PCB, housed in the electrical cover. There are 2 slots for directly connecting the option module to the control module and where those slots are already filled, the option card can be fitted on top of the existing modules. The modules can be stacked 2 high where a ‘deep’ electrical cover is fitted.

Back of the control module

Fig 3: The MFU and its location behind the control module in an IQ3

With the IQ3 actuators, the remote inputs are always present (they are conditioned by the control board) 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 an Extra Relay Indication card associated with these outputs must be fitted into another option slot in the actuator.

The MFU is connected to the control module by a 10 way header (SK2). The wiring harness from the actuator terminal bung connects the Modbus RS-485 field connections to SK3.

3.2 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 electrical housing cover should be removed after unscrewing the four 6mm Allen machine screws. Unplug the electrical housing loom from the control board and remove the cover. Unplug the grey ribbon cable from the edge of the control board and unplug the black plastic carrier frame from the frame legs. Unplug the loom from the MFU card. Unscrew the Torx 20 screws holding the MFU card into the frame and carefully unplug the MFU card

Option Slots

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from the control board. The replacement board is fitted in the reverse order to removal. The wiring harness connectors are polarised so that only the correct one will fit its mating part on the circuit boards. Don’t forget to re-connect the grey ribbon cable to the edge of the control board.

If the operation is to fit an MFU for the first time, then the necessary wiring loom must be added to the internal wiring harness of the actuator. The actuator wiring diagram shows the connectors and harness used. The wiring harness is fitted inside the actuator before attempting to fit the MFU. This requires that you remove the terminal bung, which is held in place by a large circlip. Be careful to attach the wiring loom to the correct terminals, which are numbered. Re-fit the terminal bung.

Once the loom is in place, connect it to the MFU, then fit the MFU to the actuator main board connector. Attach the MFU to the frame, using the Torx 20 screws.

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. Modbus parameters can be set and adjusted either by using the Infra-red and Bluetooth setting tools

or by Insight 2 using Bluetooth. The parameter setting procedure is covered by the IQ3 Full configuration, status and monitoring user manual, PUB002-040, available on the Rotork web site,

www.rotork.com

3.3 Inside an SI₃ actuator

The MFU is suitable for fitting into SI3 actuators. When factory-fitted, the network connections will be as in the diagram below:

The internal layout of the actuator will be similar to that of the IQ3, when considering installation of the MFU, as above.

Modbus Option Card Properties

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3.4 Inside a CVA actuator

The single channel MFU is suitable for fitting into CVA actuators. When factory-fitted, the wiring diagram will be CXX-40 (where X can be any value). This details the option card connections to the terminal bung. The MFU module is fitted in the only option board slot inside the CVA electrical housing

- on the underside of the Main PCB assembly. The MFU should be replaced or fitted only in a suitable environment.

Fig 4: The MFU located on the underside of the control PCB in a CVA actuator

To fit an MFU card, begin by removing power from the actuator and wait until the LED on the selector knob stops illuminating. This may take several minutes if a reserve power pack of capacitors is fitted.

Remove the six M10 machine screws from the upper cover and lift it off carefully, while removing its ribbon cable connector from the socket on the Main PCB.

Remove the various wiring looms from the sockets on the edges of the Main PCB, noting carefully where they attach. Each connector is different to avoid error.

Remove the Main PCB in its plastic chassis by gently pushing the chassis legs inwards to release them from a groove in the actuator housing.

Fit the MFU to the underside of the Main PCB using the hardware supplied with the MFU card. The wiring loom from the actuator terminal bung connects the Modbus RS-485 field connections to

SK3. If a new card is being fitted as an upgrade, then the actuator will need to have the loom fitted. Remove the terminal bung by removing the circlip and gently pulling the bung. Attach the loom and replace the bung.

The MFU is connected to the control module by a header, SK2. The MFU in the CVA must be enabled. This would usually be done during factory test, but may be

required to be completed on site for conversions to Modbus or if a replacement card is fitted. To enable the card, the Rotork PDA software Enlight (downloadable from the Rotork web site) is required to be used to change parameter 34. It must be read and then 2048decimal added to it.

This procedure is best performed by a Rotork Engineer.

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3.5 Inside a CMA actuator

The MFU is suitable for fitting into CMA actuators, wiring diagrams MXX-MX (where X can be any value) detail the option card connections on the terminal strip. The MFU module is fitted in the only option board slot inside the CMA electrical housing.

Fig 5: The MFU located in a CMA actuator

Only the single channel Modbus option card can be fitted to this actuator family. The MFU should be replaced or fitted only in a suitable environment. The actuator must be made

electrically safe before opening any covers. The electrical housing cover should be removed after unscrewing the four 6mm Allen machine screws.

The MFU should be fitted in the position shown in the illustrations above. It plugs into the control board at the 10-way header, which is SK2 on the MFU board. There is a wiring loom which brings the RS-485 network connection to SK3 on the MFU. This loom comes from SK5 and SK6 of the Modbus terminal board, which in turn is where the field network connections are made.

Connection details are shown in the illustrations on the next page. The CMA actuator will need configuring, so that it is aware that control from the field is through the

MFU card. This is done by accessing the menu structure shown in figures 7, 8, and 9. Configuration details may be found in the CMA Installation and Maintenance manual, PUB094-003,

found on the Rotork web site.

Option location

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Fig 6: CMA menu structure for setting up the actuator: start at the BASIC setting and select the ADVANC button.

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Fig 7: CMA menu structure for setting up the actuator: from the ADVANC setting, select the COMMS button.

Modbus Option Card Properties

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Fig 8: CMA menu structure for setting up the actuator: from the COMMS setting, select the Modbus button. From here, you can adjust the individual Modbus settings.

Fig 9: Connections to the MFU located in a CMA actuator

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3.6 Inside a K-Range actuator

The MFU is suitable for fitting into K-Range actuators; wiring diagrams similar to 1612ZMD detail the option card connections. The MFU module is fitted in the only option board slot inside the K-Range electrical housing.

SK2 on the MFU card plugs directly onto SK9 on the Main card, while a terminal bung loom brings the network Modbus signals to SK3 (shown on right hand side of photograph) on the MFU card.

Modbus Option Card

Main Card

Fig 10: The MFU located in a K-Range actuator

The MFU card is attached to the main card by three plastic pillars, with one metal pillar, Torx 20 screw and a fibre washer; as shown in the photograph above.

If an actuator is having the MFU fitted for the first time, then the terminal bung loom must also be fitted. The terminal numbers will be found in the appropriate wiring diagram, which should be included in the fitting kit.

Modbus Option Card Properties

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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, and 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 or electronics module is powered up. (The actuator may have an auxiliary power supply attached, so that actuator position can be reported even when the main actuator supply is removed).

T = Terminator

PLC

Screened cable throughout

Fig 11: Typical RS-485 Data Highway

The data highway must be terminated with a resistor of 120 ohms at each end. One of the terminators must be an active termination. This requires a 5 volt DC power supply. The negative side of the supply is attached to the data negative wire by a 560 ohms resistor. The positive side of the supply is attached to the data positive wire by another 560 ohm resistor. Data positive is the wire which has a positive voltage on it compared to the data negative wire when a logic 1 pulse is on the highway.

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 Modbus standard permits up to 32 devices to be connected per segment, though one of these devices 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 of the MFU is 247.

The length of the highway will determine the maximum speed for the data transmission. The greater lengths are achieved at the lower transmission speeds.

Although RS-485 requires only 2 wires for data transmission, the Modbus standard also requires that all the nodes on the network have a maximum common mode differential of -7 to +12 volts. This requires the ground potential at all points to be within the -7 to +12 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 for this, Rotork provides a ‘common’ terminal on the actuator. The common wire is shown in red above in figure 9.

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With RS-485 the data passes over a single 2-wire cable, but the Modbus protocol is such that 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, which forms the active terminator. The MFU does not contain biasing components and therefore requires biasing to be made externally. If the PLC does not do the biasing, then an active terminator must be fitted to the network highway and it will provide the necessary biasing.

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 spur 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 daisychain. All the configurations require the cumulative total of the stub lines to be kept within the permitted maximum for the network speed to be used. A combination of both topologies may be used. Topologies, such as ring and star are non-standard and should not be used with standard Modbus hardware. However, a ring network can be achieved using the single channel with repeater hardware.

It is good practice to avoid spur lines wherever possible.

PLC

SPUR

TAP

TRUNK CABLE

TAP TAP TAP TAP

TAP

PLC

TRUNK CABLE

Fig 12: RS-485 Data Highway Topology

The maximum trunk length, length of each spur and the cumulative total are dependent on the system speed in use. The table below suggests the maximum figures for copper cable. The segment length is the total of the trunk and all the spurs added together.

Data Rate (Baud)

Maximum Segment Length (m)

Total Spur Length (m)

9,600

1,500

500

19,200

1,200

500

38,400

1000

300

57,600

750

200

115,200

500

100

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.

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