What Is an Industrial Gateway? Types and Selection Criteria

An industrial gateway translates the data of field devices using different interfaces or protocols, such as Modbus RTU on RS-485, and passes it to Ethernet and higher-level systems.

Original Welibaba illustration of Industrial Gateways

An industrial gateway is a communication device that translates data between devices using different interfaces or protocols, connecting field devices to a higher-level network. Its most common use is to carry data from analyzers, meters, relays and PLCs using Modbus RTU on RS-485 onto Ethernet with Modbus TCP, and on to SCADA or energy monitoring software. An Ethernet switch that only adds ports, or a repeater that only regenerates the RS-485 signal, cannot replace it.

How it works

In Modbus RTU a master polls the slave devices one by one by address. SCADA on the Ethernet side sends a Modbus TCP request; the gateway passes it to the RS-485 line as a Modbus RTU query and translates the reply back.

Types

Ethernet–RS-485 gateway: Opens an RS-485 line to Ethernet. The Tense ETH-GTW models are of this type, with 24 V and 230 V supply versions.
Device-specific gateway: Links one product family to Modbus; the GEMO AR2-S-24VDC-MB1 connects the AR2 smart relay to a Modbus RTU network.
Wireless concentrator: Collects data from wireless sensors and meters and serves it over Modbus; the Schneider Electric PAS600 and PAS600L EcoStruxure Panel Server.
Data logger and energy server: Also stores and displays data on the device; the PAS800, PAS800L and the PoE-powered PAS800P.

Selection criteria

Field side: The interface (RS-485, wireless) and protocol of the devices. All devices on one RS-485 line must use the same baud rate and parity.
Upper-system side: The protocol SCADA expects (Modbus TCP, web interface, HTTPS) and whether the gateway acts as client or server. Check in the datasheet which mode the catalog models support.
Number of devices: Modbus addresses run from 1 to 247; TIA/EIA-485 allows 32 unit loads per line. Check the supported device count in the datasheet; beyond it, split the line or add a repeater.
Data logging: Choose a data-logging model if there is no separate server or data must survive a lost connection.
Supply: 24 V DC, 110–277 V AC/DC, 230 V or PoE; choose the one that matches the panel supply.
Access security: Do not expose the gateway directly to the internet, change the default password and use a VPN for remote access.

Common mistakes

Wiring the RS-485 line as a star or forgetting termination: Run a daisy chain with a termination resistor at both ends; otherwise reflections disrupt communication.
Swapping A and B: Manufacturers may label A/B (or D+/D−) differently; if a device does not respond, check the wires first.
Giving two devices the same address on one line: Replies collide and neither can be read.

Standards

The RS-485 physical layer is defined by TIA/EIA-485. The Modbus RTU and Modbus TCP specifications are published by the Modbus Organization.

Models in the catalog

The Industrial Gateways category lists 8 active models:

Schneider Electric (5): PAS600 and PAS800 (110–277 V AC/DC), PAS600L and PAS800L (24 V DC), PAS800P (PoE)
Tense (2): ETH-GTW-24V and ETH-GTW-230V
GEMO (1): AR2-S-24VDC-MB1

For the devices connected to a gateway see power network analyzers; for the line, see the RS-485 cables category.

Frequently asked questions

What is the difference between Modbus RTU and Modbus TCP?

Modbus RTU runs on a serial line (usually RS-485), Modbus TCP over TCP/IP on Ethernet; the default TCP port is 502. The data model is the same; the gateway translates the framing.

What is the difference between the PAS600 and the PAS800?

The PAS600 is the universal model that collects wireless devices and works as a Modbus gateway. The PAS800 additionally logs data and presents it as an energy server. The L versions are powered from 24 V DC and the PAS800P over PoE.

Which cable is used on an RS-485 line?

A shielded, twisted-pair communication cable.

How do I get a price?

Schneider Electric models are sold on a quote basis; Tense and GEMO prices are on the product page.