Today is...
Wednesday, June 20, 2018
Welcome to, the global online
community of automation professionals.
Featured Video...
Featured Video
EtherCAT with CTC’s master lets your multivendor network play well together...
Our Advertisers
Help keep our servers running...
Patronize our advertisers!
Visit our Post Archive
I/O Scanner Based on RS485 Network
I want a Solution for a Data acquisition system running on RS485 Network and working as slave for SCADA Master

Dear friends,

I am using RS485 network based Data acquisition system. The Architecture of the System is like that. There are so many RS485 based Modbus slave connected in daisy chain network in 10 RS485 Loops. all Slave devices are Connected to Intouch SCADA server through Moxa make Modbus RTU to Modbus TcP/IP Converter/Gateway. SCADA Server Accessing all device data on Modbus TCP Network by MBENET (Modbus TCP/IP) I/O Server.

The Main Problem with this architecture is that i need to configure N Nos of items (Unique item no for each Modbus Slave) in MBENET Server. when i add more devices, MBENET I/O server Performance get suffered.

I just want to inquiry that, whether there is any device available, which will be connected to all Modbus SLAVEs on RS485 Network and and acquire the data from all device in Periodic manner (I/O scanning) and store or Map these data on Internal Register (Modbus R/W register), from where SCADA Modbus Master will pickup all data through MBENET I/O Server. Hence MBEnet I/O server will see only one Modbus Slave device and no need to Configure so many items name in MBENET Server.

Kindly Note that I have no problem with amount of Data accessed by MBENet Server, because SCADA Server only reads some 2-3 analog Parameters and 4-5 Discrete Parameters at a time from each Modbus Slave device. the problem with I/O scanning of so many Devices by a single MBENet Server. the one more problem with Modbus slave devices that these device are preconfigured only for baudrate 9600 b/s and can not be changed. i have Configured and another MBEnet I/O server to distributed the Load and got some improvement in Performance, but still as other I/O server already Having some Load and Limited No of Licenses Availability for SCADA Server. i can not Configure More dedicated I/O Server for data acquisition.

Please provide any solution for this Problem or Suggest me any device available in Market which can fulfil my Requirements.

1 out of 1 members thought this post was helpful...

Hello krkumar,

You may want to change your Moxa Gateway with small PLC that have two interface : Modbus TCP (ethernet)!and Modbus RTU (RS-485). The ethernet side will be connected to your HMI while RS-485 side will be connected to daisy chain network of Modbus slave so it will acting as modbus RTU master. PLC that you can use, for example is Twido PLC, a small PLC from Schneider which has native communication port for both Modbus TCP and Modbus RTU. PLC then read/write all data required from each slave thru modbus RTU and then consolidate all of data gathered from each slave into internal memory. MBENET then will read/write this memory location thru modbus TCP.

With this architecture, you only need one MBENET topic, please remember that item represented each modbus memory location on each slave, while topic represented modbus slave). By use only one topic you will get the update time of Intouch improved.

From RS-485 side, you may want to improve the communication speed by arrange modbus data to be accessed in one block, so Modbus master will be able to gather/ update multiple data on each slave in one shot.

Best regards

Dear ann

its ok to use twido plc, but problem with PLC is that only one port (Modbus RTU)available. i have different instrument located in whole plant area connected in 6 Daisy chain RS485 network.

Dear krkumar,

there is Twido controller that have built in communication ports for boths Ethernet port and RS-485 port in one compact controller. the PN is TWD LCAE 40DRF, please check below datasheet:

You can connect your wonderware intouch to the Twido ethernet port using Modbus RCP and MBENET driver, while in the same time use the Twido RS-485 port to connect to your daisy chain RS485 network
using Modbus RTU protocol.

Best regards

To solve the problem, translate the various protocols, simplify and speed up data communication, have you consider an OPC Server?

>I am using RS485 network based Data acquisition system. The
>There are so many RS485 based Modbus slave connected

By automationtechie on 20 March, 2017 - 2:15 pm

Hi Krkumar,

We have a product which performs in that manner. It is our Modbus Data Concentrator. Please see link below.

The MDC is configured with a preset list of Modbus ID/Modbus Addresses. It will poll these Modbus registers continuously in the order configured. It will store these data values into it's own internal memory and will be able to be polled for this data using a single Modbus poll (as a Modbus TCP Slave) at the MDC's IP address.

For larger networks, you can use multiple MDC.