Serial to Ethernet – Media and Protocol

By Brian Gallogly

It’s always interesting when I talk to people about Serial to Ethernet.  They mostly only think of the Media (connectors and wire type) which is from RS-232/422/485 to a RJ45 Ethernet port on either a PLC CPU, an unmanaged Ethernet Switch, or a Managed Ethernet Switch.  What they usually leave out is that there is a protocol conversion that needs to be done as well like going from Modbus/RTU to Modbus/TCP for example.

Sensors – There are 3 major types:  There are one-way communication types such as Discrete (on/off) and Analog (+/- 100%) in either Voltage (1-5V) or Current (4-20ma).  Then there are two-way Serial (RS-232/422/485) communication types such as:

• Analyzers (Gas, Liquid, and Solids for Power Generation, Petrochemical, and Water Industries)
• Inverters (Solar Industry)
• VFD/VSD/Inverters (Controlling the speed of motors with Amperage Feedback)
• Smart Sensors (Voltage Monitors, Weather Stations, Complex Level & Flow)

A common way of getting the sensor data to a SCADA system is to use a PLC or a DCS whereby the CPU cards have a Serial port that accepts Modbus/RTU plus the IO cards that are either Discrete or Analog.  All the newer PLC CPU ports have Ethernet ports as well which supports the 3 major Industrial Ethernet protocols:  Modbus/TCP (ADC/Modicon/SQD/Omron/Idec/Mitsubishi), EtherNet/IP (Mostly Rockwell AB), and PROFINET (Mostly Siemens).

For the older PLCs that do not have Ethernet ports and for Analyzers that are not hooked up to a PLC, there is a way for them to communicate to a SCADA / IIoT / IoT platform.
Moxa offers a Gateway for the above situations (0-60 deg C).  Wider Temp models available.

MGate MB3170i – From Modbus/TCP, ASCII, or RTU to Modbus/TCP, ASCII, or RTU
MGate 5105-MB-EIP – From Modbus/TCP, ASCII, or RTU to EtherNet/IP
MGate 5102 – From Modbus (any) or EtherNet/IP to PROFINET
We have a special going on right now for the most popular model, the MGate MB3170i
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$282/each (through June 1, 2023) with over 500 units in stock at Quantum Automation.
Datalogging and Trending of Analyzed Data at a SCADA or IIoT Centralized Location can help determine potential issues to minimize downtime but can also provide information to increase productivity and provide a safer environment.