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What’s the difference between HART/BRAIN/MODBUS and PROFIBUS?
Dec 25, 2018


The HART Communication Protocol (Highway Addressable Remote Transducer) is a hybrid analog&digital industrial automation open protocol. Its most notable advantage is that it can communicate over legacy 4–20 mA analog instrumentation current loops, sharing the pair of wires used by the analog only host systems. HART is widely used in process and instrumentation systems ranging from small automation applications up to the highly sophisticated industrial applications.


The BRAIN protocol is an agreement of Yokogawa Smart Instruments. It has this protocol in Yokogawa transmitters, vortex streets, electromagnetic flowmeters, etc. The handheld intelligent terminal used with this protocol is BT200, which support transmitters’adjust and monitoring.


Modbus is a serial communications protocol originally published by Modicon (now Schneider Electric) in 1979 for use with its programmable logic controllers (PLCs). Modbus has become a de facto standard communication protocol and is now a commonly available means of connecting industrial electronic devices. There are four features make Modbus used widely :

3.1openly published and royalty-free

3.2easy to deploy and maintain

3.3moves raw bits or words without placing many restrictions on vendors

3.4developed with industrial applications in mind


PROFIBUS (Process Field Bus) is a standard for fieldbus communication in automation technology and was first promoted in 1989 by BMBF (German department of education and research) and then used by Siemens. It should not be confused with the PROFINET standard for Industrial Ethernet. PROFIBUS is openly published as part of IEC 61158. There are two variations of PROFIBUS in use today; the most commonly used PROFIBUS DP, and the lesser used, application specific, PROFIBUS PA.

PROFIBUS DP (Decentralised Peripherals) is used to operate sensors and actuators via a centralised controller in production (factory) automation applications. The many standard diagnostic options, in particular, are focused on here.

PROFIBUS PA (Process Automation) is used to monitor measuring equipment via a process control system in process automation applications. This variant is designed for use in explosion/hazardous areas (Ex-zone 0 and 1). The Physical Layer (i.e. the cable) conforms to IEC 61158-2, which allows power to be delivered over the bus to field instruments, while limiting current flows so that explosive conditions are not created, even if a malfunction occurs. The number of devices attached to a PA segment is limited by this feature. PA has a data transmission rate of 31.25 kbit/s. However, PA uses the same protocol as DP, and can be linked to a DP network using a coupler device. The much faster DP acts as a backbone network for transmitting process signals to the controller. This means that DP and PA can work tightly together, especially in hybrid applications where process and factory automation networks operate side by side.