**PROFIBUS-DP Communication Distance and the Use of Repeaters**
In PROFIBUS-DP communication, the maximum transmission distance is directly related to the baud rate. Higher data rates result in shorter allowable distances due to signal degradation over longer cables. Therefore, when a system requires longer distances than what the selected baud rate allows, a repeater becomes essential.
A repeater is used to extend the communication range by amplifying and regenerating the signal between two segments of the bus. It ensures that the signal remains strong and clear, allowing for reliable communication across extended distances.
One of the key features of a repeater is its ability to automatically detect and adjust the data transfer rate. This includes:
- A data transfer rate of 45.45 kbit/s
- A 24 V DC power display
- Display of bus status for segment 1 and segment 2
- Isolation of segments using a switch
- Isolation of segment 2 when the terminating resistor is enabled
- Decoupling of segments during static interference
- Increasing the number of devices on the bus
- Optical isolation between segments
- Debugging and startup assistance
- A switch to disconnect segments
- Display of bus activity
- Isolation of incorrectly inserted segments
The repeater must be placed between two segments of the bus. As shown in Figure 1, it has four connection points: A1B1, A1'B1' for segment 1, and A2B2, A2'B2' for segment 2. The repeater only amplifies the signal between these two segments, not within them.
It is important to note that if one segment is not connected, the terminating resistor should be turned ON. This helps maintain signal integrity and prevent reflections that can cause communication errors.
The MODE switch on the repeater is critical and should never be turned OFF. If it is, the two segments will be completely isolated, and no signal will pass through, effectively disabling the repeater’s function.
Figure 2 shows the internal circuit diagram of the repeater. It illustrates how the terminating resistors (S1 and S2) are used to connect or isolate the bus segments. When the terminating resistor is ON, the corresponding bus segment is properly terminated, ensuring signal stability.
Figures 3, 4, and 5 demonstrate the cable length that a repeater can support under different wiring configurations, assuming a transmission rate of 1.5 Mbit/s. These figures help users determine the optimal placement and configuration of the repeater based on their specific network requirements.
In summary, using a repeater in a PROFIBUS-DP network is crucial for extending communication distances while maintaining signal quality. Proper setup, including the correct use of terminating resistors and the MODE switch, ensures that the repeater functions as intended and supports reliable, long-distance communication.
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