Basic difference between Modbus RTU RS485 and Modbus TCP/IP for Solar Power Plants Applications
Modbus RS-485 & Modbus TCP/IP interfaces are widely used in the industry for connecting & monitoring various equipment.
Modbus RTU RS485: Remote Terminal Unit (RTU) Modbus over a serial RS485 connection
Modbus TCP: Modbus over an Ethernet connection
The following table covers the basic differences with respect to its applications in Solar Equipments.
Modbus RTU RS485 |
Modbus TCP/IP |
| RTU is in existence for long around, and it is supported by lots of Inverter , meter & sensor manufacturers | Modbus TCP/IP is easy to integrate & can be used with existing Ethernet network equipments (Intranet or Internet), which are inexpensive and widely available. |
| Max no. of 32 devices in one segment | Upto 256 |
| The maximum distance of RS-485 without using a repeater is 1.2km at baud rates up to 90Kbps. | Depends on capacity of communication cable (Ex- 100m with Cat6). It can use existing intranet/internet network. |
| Can reach 10 Mbit/s at 10m. (Speed of operation depends on length of the line ) |
Modbus/TCP will be sent at speed of your Ethernet connection (Most Modbus/TCP hardware these days is 10 or 100 Mbit/s) |
Some Frequently Asked Questions
How many slaves can be connected for other protocols such as RS232 ?
- RS-232 only allows for one slave.
- RS-422 can address up to 10 slaves.
- RS-485 can address up to 32 slaves.
Can i monitor more than 32 slaves on Rs485
Our Modbus RTU supports the node range from 0-255. After 32 nodes (1 master + 31 slaves), you may need RS-485 repeaters to ensure proper communications. This depends on a number of different items, including if the RS485 transceivers are full or quarter load.
Can i extend RS-485 network beyond 1.2KM?
RS-485 network distance can be extend by adding RS-485 repeater or optically Isolated Repeater every 1.2KM
References
1) Modbus Messaging on TCP/IP Implementation Guide V1.0b (PDF), Modbus Organization, Inc., October 24, 2006, retrieved 2017-01-07
2) “Modbus Application Protocol V1.1b3” (PDF). Modbus. Modbus Organization, Inc. Retrieved 2 August 2013.