What is MODBUS?
MODBUS is a communication protocol used in industrial automation systems to allow devices to talk to each other. Think of it as a common language that sensors, controllers, and computers can use to exchange information reliably.
Modbus, created in 1979 by Modicon, the original maker of the Programmable Logic Controller (PLC) is a protocol specifically designed to enable the exchange of process data between industrial control devices.
What Does Modbus Mean?
The term MODBUS comes from:
MOD – from Modicon, the company that created it.
BUS – refers to a communication bus, meaning multiple devices share the same communication path.
So basically, MODBUS = a communication system/protocol from Modicon.
What Does Modbus Work?
MODBUS is a way for fixed gas detectors in a factory or industrial system to talk to each other.
Master and Slaves
The master, which can be a computer or PLC, controls the communication and asks for information from other devices. The slaves, such as sensors, meters, or valves, respond by sending the requested data back to the master. A single master can communicate with multiple slaves on the same network.
How Does it Communicate?
MODBUS can send data in a few different ways depending on the network and devices being used. MODBUS RTU is fast and compact, using special wiring like RS-485 or RS-232, making it ideal for simple serial connections. MODBUS ASCII sends data as text instead of binary, which makes it easier to read but slightly slower. MODBUS TCP/IP works over Ethernet networks, similar to regular internet connections, and is suitable for modern industrial systems that need faster and more flexible communication.
How is Data Sent?
Data in MODBUS is sent in registers, which are small blocks of information that store specific values. Each register can contain data such as temperature, pressure, flow, or an on/off status. Every slave device has its own unique address, allowing the master to identify and communicate with the correct device on the network.
How MODBUS Requests and Responses Work
In MODBUS communication, the master sends a request to a slave, such as asking, “Slave 1, what’s the temperature?” The slave then responds with the requested information, for example, “The temperature is 72°C.” This request-and-response process allows the master to collect data from multiple devices on the network.
Gas Detectors That Use MODBUS
Crowcon XgardIQ Fixed Gas Detector
The Crowcon XgardIQ is a fixed‑gas detector and transmitter that includes RS‑485 Modbus RTU as a standard output option alongside the more traditional 4‑20 mA analogue output. This means instead of (or as well as) sending a simple current loop signal, the XgardIQ can communicate digitally, transmitting detailed information such as gas concentration, detector status, alarm conditions or fault signals directly to a control system (e.g. PLC, DCS or SCADA) over a Modbus network.
For more information on this product, please visit: Crowcon XgardIQ Fixed Gas Detector | Rockall Safety
Honeywell Sensepoint XCL Fixed Gas Detector
The Honeywell Sensepoint XCL can communicate using MODBUS RTU, allowing it to send digital data to a control system such as a PLC, DCS, or SCADA. Instead of relying solely on the traditional 4–20 mA analogue output, the detector can transmit detailed information over a serial network, including gas concentration readings, alarm conditions, and fault status.
For more information on this product, please visit: Honeywell Sensepoint XCL Fixed Gas Alarm | Rockall Safety
