Although being around since 1989, PROFIBUS still dominates serial Fieldbus technology. It’s true that industrial data communication is gradually moving towards Industrial Ethernet. PROFIBUS, however, still has a promising future.
Due in large part to two characteristics, PROFIBUS Connector is widely used and well-liked in the manufacturing and process industries: its capacity to meet complicated automation needs and its ability to communicate across devices made by various manufacturers without requiring interface adjustments.
The PROFIBUS DP and PROFIBUS PA are the two variations. Because to its prevalence in industrial applications, PROFIBUS DP is the one that is regarded as “the standard” of the two. Nonetheless, both types are equally effective for complex communication tasks and crucial applications and use the same communications protocol.
Yet, there are important distinctions, so let’s look at them.
How to use PROFIBUS DP?
Decentralized Peripherals is what the DP stands for. It employs the RS-485 as its physical layer, enabling long cabling distances in electrically noisy situations and being able to handle numerous devices on the same bus. It was created for a variety of manufacturing and process automation applications.
High transmission speed and straightforward data interchange are PROFIBUS DP’s key characteristics. It can operate between 9.6kbps and 12Mbps baud speeds. Moreover, the relationship between the maximum cable length and baudrate is inverse. In other words, the wire gets shorter the higher the baudrate.
Actuators, frequency converters, HMI panels, and remote IO are examples of common devices. The worldwide PROFIBUS organization has standardized the specifications for the 2-wire (twisted single pair) cable used to carry signals (PI).
With PROFIBUS DP, all devices are typically linked to the cable in parallel using bus topologies (see picture below). One segment can include up to 32 nodes, although repeaters can be used to expand segments and build various topologies. In order to separate electrical disturbances, repeaters can also act as galvanic isolation between electrical segments.
How does the PROFIBUS PA operate?
Process Automation is referred to as PA. It was created for the context of process automation, which frequently calls for slower processes and may be exposed to dangerous or explosive situations. Interoperability and safety are crucial in this situation.
Manchester Encoded Bus Powered Intrinsically Secure (MBP-IS), the physical layer of PROFIBUS PA, enables synchronous data transfer. PROFIBUS PA carries data and power over the same two wires of the connection, in contrast to DP. Even though the cable properties vary, PI has still standardized them.
Because it restricts the power travelling to the field, this architecture’s intrinsic safety feature is especially well suited for devices placed in hazardous areas. As a result, Modbus’ standard confinement technique is no longer required.
The signal baudrate with this variation is another distinction. 31.25Kbps is used by PROFIBUS PA. The adoption of star and other topologies is facilitated by these physical and signalling modifications (see picture below). The planned safety environment or the Ex Zone determines the cable length (the rated Explosion Hazardous Area).
Due to the high cost of controllers made for hazardous situations, PROFIBUS PA employs DP/PA couplers or links to link controllers or masters of PROFIBUS DP to PROFIBUS PA devices. Similar to PROFIBUS DP repeaters, DP/PA couplers operate. But on one side, they have a PROFIBUS DP interface, and on the other, a PROFIBUS PA interface. DP/PA couplers have the drawback of only allowing data to be transferred at one sluggish baudrate, which might cost the user a lot of money. The DP/PA Connections are more intricate. Simply put, DP/PA connections have a buffering scheme to allow for the usage of all PROFIBUS DP baudrates.
Conclusion:
The message protocols used by PROFIBUS DP and PROFIBUS PA are the same, and both are widely used in industrial automation. Yet every variation has a different use in mind.
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