Modbus RTU uses a daisy chain network, so you can link the whole network on two wires and communicate with each device by providing each node with a unique address. Modbus TCP uses a star network where each node has an individual cable called a Cat5 or Cat6. They can be connected with the use of a router.
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What is the difference between a RTU and TCP meter?

The main difference between Modbus RTU and Modbus TCP meters lies in their communication protocols and underlying physical layers. Modbus RTU is a serial protocol typically used with RS-232 or RS-485 interfaces, while Modbus TCP is an Ethernet-based protocol.

Modbus RTU uses a daisy chain network, so you can link the whole network on two wires and communicate with each device by providing each node with a unique address. Modbus TCP uses a star network where each node has an individual cable called a Cat5 or Cat6. They can be connected with the use of a router. They also come with a personal address unique to each node on the network. The address can be from 1 to 255, which means theoretically, you can have 254 units on the same network. You can also use Modbus TCP over the internet.

Here's a more detailed breakdown:

Modbus RTU:

  • Communication: Uses serial communication (RS-232 or RS-485).
  • Physical Layer: Relies on serial communication interfaces.
  • Speed: Typically slower than Modbus TCP.
  • Distance: Suitable for shorter distances (RS-485 enables up to 1,200 meters of communication).
  • Cost: May be more cost-effective for simpler, smaller systems.
  • Complexity: Generally simpler to set up and troubleshoot in terms of network configuration. 

Modbus TCP:

  • Communication: Uses Ethernet and TCP/IP.
  • Physical Layer: Relies on Ethernet networks.
  • Speed: Generally faster than Modbus RTU.
  • Distance: Suitable for longer distances (e.g., across a large facility or even remotely).
  • Cost: May involve a higher initial investment due to Ethernet hardware requirements.
  • Complexity: May require more advanced network configuration and troubleshooting. 

In simpler terms:

  • RTU:
    Like a walkie-talkie, where only one person can talk at a time (half-duplex), and it's better for short distances and simpler setups.
  • TCP:
    Like a phone, where multiple people can talk simultaneously (full-duplex), and it's better for faster, longer-distance communication and more complex setups. 

Key takeaways:

  • Modbus TCP is generally preferred for modern industrial systems requiring high-speed data exchange and integration with IT networks. 
  • Modbus RTU remains relevant for legacy systems, simpler applications, or when cost is a major factor. 
  • For systems requiring both protocols, Modbus gateways provide seamless integration between RTU and TCP networks. These devices translate communications between the two protocols allowing hybrid network configurations. 

While still supporting the Modbus RTU protocol and its supported meters, Maxem prefers to work with Modbus TCP meters. The benefits in speed, distance, and reliability will not only improve your measurements and therefore robustness, but will also make your system future-proof for improvements and expansion.

Which Modbus kWh-meters are compatible with Maxem? Please, read here.