Sentera Controls MODBUS RTU User manual

24 VDC + Modbus RTU
24 VDC + Modbus RTU
24 VDC + Modbus RTU
Installation guide
Modbus RTU

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Table of contents
SAFETY AND PRECAUTIONS 3
DESCRIPTION 4
HOW IT WORKS 4
POWER OVER MODBUS SUPPLY (PoM) 5
DATA TRANSMISSION 7
MODIFY OR MONITOR PARAMETERS 10
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SAFETY AND PRECAUTIONS
Read all the information, the datasheet, mounting and operating instructions and
study the wiring and connection diagram before working with the product. For
personal and equipment safety, and for optimum product performance, make sure you
entirely understand the contents before installing, using, or maintaining this product.
For safety and licensing (CE) reasons, unauthorised conversion and/ or modifications
of the product are inadmissible.
e product should not be exposed to abnormal conditions, such as: extreme
temperatures, direct sunlight or vibrations. Long-term exposure to chemical
vapours in high concentration can affect the product performance. Make sure the
work environment is as dry as possible; avoid condensation.
All installations shall comply with local health and safety regulations and local
electrical standards and approved codes. is product can only be installed by an
engineer or a technician who has expert knowledge of the product and safety
precautions.
Avoid contacts with energised electrical parts. Always disconnect the power
supply before connecting, servicing or repairing the product.
Always verify that you apply appropriate power supply to the product and use
appropriate wire size and characteristics. Make sure that all the screws and nuts
are well tightened and fuses (if any) are fitted well.
Recycling of equipment and packaging should be taken into consideration and these
should be disposed of in accordance with local and national legislation/regulations.
In case there are any questions that are not answered, please contact your
technical support or consult a professional.
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MODBUS RTU

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DESCRIPTION
Sentera devices exchange information via a network, called Modbus RTU.
Modbus is a serial communication protocol developed by Modicon® in 1979 for use
with its programmable logic controllers (PLCs). In simple terms, it is a method used
for transmitting information over serial lines (RS485 technology) between electronic
devices. e device requesting the information is called the Modbus Master and the
devices supplying information are Modbus Slaves. On a standard Modbus network,
there is one Master and up to 247 Slaves, each with a unique Slave Address from 1
to 247. e Master can also write information to the Slaves.
e official Modbus specification can be found at: http://www.modbus.org/
ATTENTION Each Modbus RTU network requires one master and one or multiple slave devices.
e slave devices send information to the master device.
HOW IT WORKS
Modbus is transmitted over serial lines between devices. e simplest setup would
be a single serial cable connecting the serial ports on two devices — a Master and
a Slave.
e Master unit can be placed at any point on a bus, while still respecting a bus
topology. Even though most diagrams shown in the «Typical Network Configurations»
section always depict the Master at either end of a bus, it can also be placed in
between two slave devices (see Fig. 1).
Fig. 1 Modbus Master and Slaves
Master
Master
Slave Slave Slave Slave
Slave Slave Slave Slave
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ATTENTION Do not use a star topology!
ATTENTION Avoid making stubs on the line. If stubs are present on the network they should
be kept as short as possible.
Fig. 2 Connections
RSMFM-2R
Mulfunconal room
transmier
RSMFM-2R
Mulfunconal room
transmier
24 VDC + Modbus RTU
Main line
Stubs
24 VDC + Modbus RTU
24 VDC + Modbus RTU
DPOM8-24/20
DIN rail Power over
Modbus module
HMU-RDPU
Remote Domesc Processing Unit
with HCU rmware
ATTENTION e combined length of all stubs should not exceed 20 m.
POWER OVER MODBUS SUPPLY (PoM)
‘PoM’ or ‘Power over Modbus’ means that both Modbus RTU communication and 24
VDC power supply are distributed via one Unshielded Twisted Pair (UTP) network
cable with RJ45 connectors.
Fig. 3 RJ45 cable
/B
A
GND
24 VDC
8 mm
8 mm
8 mm
8 mm
RJ45
1
2
3
4
5
6
7
8
1
2
3
4
5
6
7
8
ATTENTION Do not directly connect the PoM cable to the Ethernet port of a computer.
Larger networks containing many devices, should be split into different segments.
For each segment, the maximum current consumption should be limited to maximum
1,5 A.
To select the correct power supply, calculate the total sum of the maximum current
consumption of all connected devices in the segment. Select a power supply with
sufficient capacity to provide power supply to all connected devices, based on this
sum. We advise to use not more than 90 % of the maximum capacity of the power
supply to compensate power losses in the cables.
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Fig. 4 Supplying different devices using DPOM
a. One DPOM
DPOM DMDBM DIG-M
RCMFM-2R OCMFM-R RCMFM-2R
Imax 840 mA
Total sum: RCMFM-2R+ OCMFM-R + RCMFM-2R + DIG-M = 316 mA
100 mA
16 mA
100 mA 100 mA
Power supply module Distribution box
b. Two DPOMs
DPOM
DPOM
DMDBM DMDBM
RCMFM-2R OCMFM-R DTS-M
DTP
Imax 840 mA
Imax : 840 mA
Modbus RTU (A and /B)
DIG-M
RCMFM-2R
e maximum current capacity of an RJ45 connector is limited to 1,5 A. Make sure
that the sum of the maximum current consumption of all devices in one segment
does not exceed 1,5 A. If necessary, create an extra segment by adding another
‘DPOM’ power supply. In most cases, the power supply will be the limiting factor.
e DPOM power supply has a maximum current capacity of 840 mA. e different
DPOM power supplies must only be connected via Modbus RTU (signal A and /B).
ATTENTION Do not interconnect the 24 VDC of the different DPOM power supplies!
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For this purpose, DPOM features an input channel with only Modbus RTU
communication. e output channel provides Modbus RTU and 24 VDC power supply.
We advise to connect the different devices in the segment to the output channel of
DPOM and to use the input channel to interconnect the different DPOM devices in
the Modbus RTU network. If necessary, a splitter device ‘DMDBM’ or ‘DLDBM’ can be
used to create extra connection points.
In case your project includes devices with 3,3 VDC power supply, the optional module
DLDBM is required (for further details go to: DLDBM22) . DLDBM derives 3,3 VDC
from the 24 VDC PoM signal.
Sentera PoM devices with 24 VDC power supply require RJ45 connectors.
Sentera PoM Devices with 3,3 VDC power supply require RJ12 connectors.
DATA TRANSMISSION
In order to optimise the transmission of data via Modbus RTU, the installer should
pay extra attention to following points:
Cable length
ere are limitations to the total cable length on a Modbus RTU network. When
the total cable length becomes too high, the Modbus RTU communication will be
disturbed. To compensate these communication losses due to cable length, a Modbus
repeater (for further details go to: DPOM-24-20) can be used to compensate cable
length:
Fig. 5 Cable length
Master
Modbus
Modbus
Slaves
max. 1000 m max. 1000 m
Slaves
max. 1000 m
Slaves
Repeater
Master
We recommend that the total cable length (*) per segment does not exceed 1.000 m.
(*) Total cable length = sum of the main network line and all branches
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Minimizing EMC pollution
In order to avoid communication disturbances, it is important that all Modbus RTU
cables are physically separated from power cables, electric motors and other sources
that can cause EMC pollution. It is recommended to use separate cable guidance for
data communication lines and power lines. Metal cable guidance systems, connected
to PE will provide the best results.
Fig. 6 Power lines and Modbus lines
Min 10 - 15 cm
Power lines
Network cables
ATTENTION Do not route the fieldbus wires close to power lines or wires leading to heavy
loads
Keep at least 15 cm distance between the sensor lines and the 230 VAC power lines.
Apart from wiring, it is essential also to separate or maintain enough distance
between more sensitive devices as sensors / distribution boxes / HVAC controllers
and power devices like frequency inverters, contactors, relays, etc.
Cable type
Two types of wires can be used based on required rigidness:
1. Twisted pair + ground and shield: long leads, disturbed environment.
2. Twisted pair with ground: short leads, no power lines in proximity.
Fig. 7 Cable types
1. Shielded twisted pair (STP) 2. Unshielded twisted pair (UTP)
ATTENTION
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e wires should have the following characteristics:
■Characteristic impedance: 120 Ω ±10%;
■Specific resistance depending on network length;
■We recommend using STP cables to minimise the risk of EMC interference;
■e cable is connected from controller to controller and no branches are allowed
on the cable.
Cable crimping
ere are two options for crimping the Modbus cable:
■If you need only the Modbus signal transmission without supply voltage, see Fig. 8.
■If you need Modbus signal and power supply - see Fig. 9.
Fig. 8 Modbus signal connection cable
Data In / Out A
/B Data Out /In
Fig. 9 Power over Modbus connection cable
Data In /Out
Data Out / In
A
/B
GND
24 VDC
-M products
Sentera products feature –M series that can be connected via an RJ45 connector.
is will provide the best results for data transmission. In case devices with terminal
blocks are used, route the wires close to the devices separating the twisted wires
only for the shortest possible distance needed for inserting them into the screw
terminals.
NBT settings
To ensure proper RS485 communication, terminating resistors are used at both
ends of a bus to reduce voltage reflections. ere must be always two terminations
or Network Bus Terminators (NBT) on the network, one at each bus end.
Every Sentera devices features an NBT that can be activated via the parameter
settings. By default, NBT is deactivated. We advise to use Sentera 3SModbus
software to activate NBT or to modify other settings in the device.
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Example 1 Example 2
RX
ТX
NBT
NBT
NBT
Slave 2
Master
Slave n
Slave 1
Slave 2
Slave 1
RX
ТX
NBT
NBT
Master
Slave n
Modbus address
On a Modbus RTU network, every device must have a unique address. By default, all
Sentera devices have the Modbus address 1. ere are two possibilities to modify
this address:
1. Via the automatic Sentera ID distribution system
In case a device with a default Modbus RTU Address ‘1’ is connected to the controller,
it will be recognized automatically. e controller will suggest a new, unique address
for this device. Follow further instructions on the RDPU screen.
2. Manually
We advise to use Sentera 3S Modbus software to modify the Modbus RTU address
or other parameters.
MODIFY OR MONITOR PARAMETERS
To modify or monitor parameters of a Sentera device via Modbus RTU, we advise
using the Sentera 3SModbus software.
e 3SModbus software was designed to activate NBT, to adjust the Modbus RTU
address or to monitor or adjust other parameters of a Sentera device. e 3SModbus
software is free and can be downloaded via our website: https://www.sentera.
eu/en/3SMCenter and installed on your computer. e Modbus to USB converter
‘CNVT-USB-RS485’ (*) allows you to connect a Sentera device to the USB port of your
computer and to monitor or adjust the different parameters.
1. Connect the A signal of the 3SModbus device to the A terminal of the CNVT-USB-
RS485.
2. Connect the /B signal of the 3SModbus device(s) to the /B terminal of the CNVT-
USB-RS485. (*)
(*) Only connect A and /B. In case GND is connected, you risk damaging the USB
port of your computer.
3. Plug the converter into the USB port of your computer. It will be recognised and
installed automatically once the connections are complete (see Fig. 10).
Fig. 10 Example of connecting Sentera’s VFSC9 electronic fan speed controller to
a computer via CNVT-USB-RS485
CNVT-USB-RS485
VFSC9
4. Connect the power supply to the Sentera device(s) which will be monitored and
/ or configured.
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5. Start the 3SM Center Software Suite and click on the 3SModbus application
button. Once you start the application, the computer will scan and automatically
recognize the connected device (see Fig. 11).
6. Once the connected device has been recognised you can monitor the input
registers and configure the device via the holding registers (see Fig. 12).
NOTE Detailed information about the Modbus input and holding registers can be
found in the mounting instruction of every Sentera product with Modbus RTU
communication.
INPUT REGISTERS
e input registers are read-only. All data can be read using the ‘Read Input Registers’
command.
HOLDING REGISTERS
ese registers are read/write registers and they can be managed via Read Holding
Registers, Write Single Register and Write Multiple Registers commands. e
registers that are not used are read-only and, therefore, writing in these registers
neither returns a Modbus error exception, nor makes any changes.
Fig. 11 3SMobdus application - example of initial scan
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Fig. 12 3SMobdus application - Input and Holding registers
Fig. 13 3SMobdus application - example of modifying a Holding registers
INSTALLATION GUIDE
MODBUS RTU