EL.CO. S.R.L. – EMS24x-xxx - INSTRUCTIONS FOR USE - Ver.01 - 05/22 – PAGE 2
3.2 - COMMUNICATION VIA RS485 MODBUS
3.2.1 - DESCRIPTION
All devices are equipped with an RS485 serial communication
interface through the bus and the terminal (Paragraph 4.4).
To keep the line at rest, the use of a termination resistor of 120
Ohm is required. The device does not mount this resistor. The
termination of the RS485 line with the 120 Ohm resistor can be
done through the terminal given as an accessory (see
Paragraph 10.6).
The communication speeds implemented range from 1200 to 38400
baud rates and allow very satisfactory performances, while
remaining well below the limits set by the RS485 standard. This
allows the wiring of the line to be made using a medium quality
shielded twisted pair: it is sufficient that the total capacity of the line
does not exceed 200nF.
The poll rate during programming and use must not be
less than 50ms.
The maximum length of an RS485 transmission is 400
meters.
3.2.2 - DESCRIPTION OF THE COMMUNICATION PROTOCOL
The protocol is a subset of the widely used MODBUS RTU protocol.
This choice guarantees easy of connection to many PLCs and to all
commercial supervision programs.
The default MODBUS address is 100.
For those wishing to develop their own application software, all the
necessary tips and information are available.
The MODBUS RTU protocol functions implemented in the EMS24x-
xxx instruments are:
function 3 - reading of n words
function 6 - writing a word
These functions (Paragraph 7) allow the supervision program to
read and edit any data of the module.
Each message contains four fields:
•slave address: the values between 1 and 255 are valid;
address 0 (zero) is reserved by MODBUS RTU for
broadcasting messages, but it is not adopted in the
EMS24x-xxx series due to the implicit unreliability of this
type of communication;
•function code: it contains 3 or 6 depending on the
specified function;
•information field: it contains the addresses or the value of
the words, as required by the function used;
•control word: it contains a cyclic redundancy check (CRC)
calculated according to the rules envisaged for CRC16.
The characteristics of asynchronous communication are: 8 bits, no
parity, one stop bit.
3.2.3 - DATA EXCHANGE
The data exchanged consist of a 16-bit word. All readable and
writable data appear as 16-bit words allocated in the device's
memory.
The operating and configuration parameters of the device can be
read and written via serial communication.
The configurable parameters are found in Paragraph 6.
INSTALLATION AND USE WARNINGS
4.1 - PERMITTED USE
The device has been designed as a measurement and
adjustment device in compliance with the EN60947-4-2 standard for
operation at altitudes up to 2000 m. The use of the device in
applications not expressly provided for by the above-mentioned
standard must provide for all appropriate protection measures. The
device CANNOT be used in hazardous (inflammable or explosive)
environments without proper protection. It should be remembered
that the installer must ensure that the electromagnetic compatibility
rules are respected even after the device has been installed,
possibly using special filters. If a failure or malfunction of the device
can create hazardous or dangerous situations for persons, animals
or property, the system must be equipped with additional
electromechanical devices to ensure safety.
4.2 - MECHANICAL ASSEMBLY
All models of the EMS24x-xxx series must be installed on a DIN rail.
Avoid placing the internal part of the device in places subject to high
humidity or dirt that may cause condensation or the introduction of
conductive parts or substances into the device. Ensure that the
device has adequate ventilation and avoid installation in containers
where devices that can lead the device to operate outside the
declared temperature limits are located. Install the device as far as
possible from sources that may generate electromagnetic
disturbances such as motors, contactors, relays, solenoid valves
etc.
Keep in mind that, once the motor starter has been installed on the
DIN bar, its only accessible part will be the front panel.
An installation that does not comply with the provisions set out in
this paragraph could compromise the declared protection levels.
4.3 - WIRING DIAGRAM
4.3.1 – EMS24x
GND-+24Vdc power
supply
ON
start motor
L1 L2 L3
load supply
T1 T2 T3
load
