How to choose HART protocol, Modbus, RS485 two-wire system?

Digital communication protocols play an important role in industrial automation.

The HART protocol, Modbus, RS485, and 2-wire are all commonly used digital and serial communication protocols.

HART protocol is a digital communication protocol, based on the Bell202 standard FSK frequency shift keying signal, in the low-frequency 4-20mA analog signal superimposed on the amplitude of 0.5mA audio digital signals for bidirectional digital communication. HART protocol is usually used for magnetic liquid level gauge, flow meters, thermometers and other instruments are widely used.

Modbus is a communication protocol based on the master-slave architecture, which uses the RS-485 serial communication standard and supports a variety of transmission methods, including serial, Ethernet, wireless, etc. The Modbus protocol is usually used in PLCs, DCSs, and other control systems in a wide range of applications.

RS-485 is a physical layer standard that defines voltages, impedances, etc., but does not give a definition of the software protocol.RS-485 allows multiple devices to share the same bus, so it can be used to communicate between multiple devices. Two-wire and four-wire are both wiring methods for RS-485, where four-wire can only realize point-to-point communication, while two-wire can hook up to 32 nodes on the same bus.RS-485 and two-wire are usually used in sensors, actuators, and other devices in a wide range of applications.

The selection of HART protocol, Modbus, RS485 and two-wire system needs to be based on specific application scenarios. For example, if you need to superimpose an audio digital signal with an amplitude of 0.5mA on a 4-20mA analog signal for bi-directional digital communication, you can choose the HART protocol; if you need a master-slave based communication protocol, you can choose Modbus; if you need to share the same bus with multiple devices, you can choose RS-485; and if you need to hook up up up to 32 nodes on the same bus, you can choose the two-wire system. If you need to connect up to 32 nodes on the same bus, you can choose two-wire system.