All About PROFIBUS: The Communication Backbone of Production Plants
What is PROFIBUS?
Available for over 20 years, the PROFIBUS standard is a mature digital fieldbus technology used in many factory and process automation applications, as well as in hybrid industries like food and beverages and pharmaceuticals. According to the PROFIBUS and PROFINET International (PI) association, over 50 million PROFIBUS devices were sold in 2015 — and this number continues to grow. Let's take a deeper dive into PROFIBUS, including what it is and how it works.
PROFIBUS, short for Process Field Bus, is a leading fieldbus communication standard in automation technology that supports the digital data exchange within a network using a single bus cable. Currently, there are two variations of PROFIBUS, the most commonly used being PROFIBUS DP (Decentralized Peripherals) for operating sensors and actuators via a centralized controller.
PROFIBUS typically uses EIA-485 transmission technology as its physical layer. Based on a shielded copper cable with a pair of twisted wires that provide an impedance of 150 ohms, EIA-485 supports the connection of up to 126 stations to one PROFIBUS DP network, supporting a linear bus topology. The Fieldbus Data Link (FDL) protocol defines the PROFIBUS data link layer. Through token passing, FDL defines the network access and differentiates between master stations and slave stations. It also controls the timeslots of the individual masters.
What Are the PROFIBUS DP Device Types?
There are three device types according to PROFIBUS DP:
- PROFIBUS DP Master Class 1. This class controls the communication process for exchanging process values, with individual slaves using the defined cyclic commands during the configured timeslots. Devices include controllers and PCs.
- PROFIBUS DP Master Class 2. This class accesses the fieldbus by using acyclic services, enabling the configuration and parameterization of intelligent field devices. Devices include engineering and operator panels.
- PROFIBUS DP Slave. These peripheral devices read input information and send output information to the periphery. Devices can process a maximum of 246 bytes of input data and 244 bytes of output data.
What Are the Network Architectures PROFIBUS Supports?
Based on the above device types, PROFIBUS can support different network architectures, including the following:
- Single Master Network. Here, only one master station — PROFIBUS DP Master Class 1 — is connected to the PROFIBUS DP network during operation. While a controller acts as the central control unit, individual slaves are connected to the fieldbus at remote locations. The single master network provides the shortest fieldbus cycle time.
- Multi Master Network. Here, several master stations — PROFIBUS DP Master Class 1 and PROFIBUS DP Master Class 2 — are connected to the PROFIBUS DP network, building independent subnetworks. Each subnetwork consists of one Master Class 1 device and appropriate slaves, or they can include additional stations for development and diagnostics. While all masters can read the slaves’ input and output values, only the Master Class 1 station configured for the slave can write the slave’s output values.
How Can I Diagnose a PROFIBUS Network?
Because PROFIBUS is a mature, robust technology, the cause of any failures is usually not a deep technical issue. Rather, the underlying problem is often a faulty connector or incorrect bus termination. Even so, finding the root of faulty behavior is not always easy. For example, PROFIBUS communication may only malfunction occasionally. You may also detect errors in seemingly unrelated parts of the overall network.
To help you detect PROFIBUS malfunctions, there are tools that provide a wide range of functionalities for conducting cable tests, electrical signal analysis and logical network analysis. Be on the lookout for our upcoming blog posts to learn more about these troubleshooting devices. We’ll also look at some PROFIBUS best practices, enabling you to keep your fieldbus up and running without any hiccups.
To learn more in the meantime, please visit our PROFIBUS Tester 5 product page.
