Definition
Modbus is the most widespread and oldest open communication protocol for exchanging data between industrial devices. It comes in two forms: Modbus RTU runs over an RS485 serial line with dozens of devices on one cable; Modbus TCP does the same over Ethernet. A master (PLC, SCADA or gateway) reads and writes values at addresses called registers in slave devices (energy analysers, drives, meters, temperature controllers). It is simple, licence-free and present in almost every device, which makes it the fastest way to start monitoring an existing plant. It has no security, so a Modbus network must be kept separate from the outside world.
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We connect existing drives, analysers and meters to the monitoring system by reading them over Modbus RTU/TCP; our Pompalog field device reads up to 120 Modbus RTU channels.