What is ProfiHub?

It is well known that to avoid reflections, PROFIBUS DP should be wired as a “linear bus”. This means that the cable daisy chains from device to device. Devices in the middle of the bus will thus have incoming and outgoing cables. Only the two devices at the cable end have a single cable connection:

The problem is that some devices use screw connections (yes it is allowed in the spec!). This means that if you need to disconnect a device, for repair or replacement, the daisy chain will be broken. Another problem is that if a wiring fault occurs, e.g. a short circuit or water ingress in a connector, then the fault will affect all the devices on the cable and it could prove difficult to locate the fault (see the tutorial “Why do we need an analyser on PROFIBUS?“).

Repeaters are often used to split a large network into several smaller segments. Because the repeater provides isolation between the two sides, each side can be wired independently. So even though each segment must be wired as a linear bus, overall the repeaters can be used to create branches:

OK, so what if we put every device on a separate branch isolated from the rest with a repeater. Then a failure in a single device should not affect the others:

Further, because each slave is on a separate segment, the cable length for each branch is independent of the others, so cables can be much longer then when using a single segment. Finally, should any problem exist on a slave/segment then only that segment will be effected, so making fault-finding a piece of cake! (Oh dear, am I going to loose out on my training courses?). This extreme case of each device on a separate segment is not necessary for every installation. However, you can perhaps see that ProfiHub provides the designer with more flexibility to isolate sections of the plant in a cost effective way.

In a nutshell (or perhaps an IP65 enclosure!), ProfiHub is five miniature repeaters in a box. Providing connections for trunk in and trunk out and five branch lines, each of which can use the maximum segment length of cable and have up to 31 devices connected. The Hubs can even be cascaded to construct tree structures. ProfiHub costs a small fraction of the price for five repeaters.

Features of ProfiHubs include:

• 5 Isolated channels (repeater segments),
• Transparent for all PROFIBUS DP protocols,
• High quality RS 485 DP specifications for each channel,
• Up to 31 devices per channel,
• 9,6 Kbps to 12 Mbps with automatic detection,
• Up to 1200 m spur line length (depends on transmission speed),
• No limit in serial placement or cascading of ProfiHubs,
• No Address required,
• Integrated termination facilities (switches),
• Single 24V DC power supply for all repeaters.

ProfiHub A5

ProfiHub B5

ProfiHub C5