Comparison Between Siemens Diagnostic Repeater and RS485 Repeater

Both the Siemens Diagnostic Repeater and a standard RS485 Repeater serve the purpose of signal amplification and regeneration in RS485-based communication networks. However, they have different functionalities, applications, and advantages.

3. Advantages and Disadvantages

Siemens Diagnostic Repeater

? Advantages:

• Improves network stability by segmenting PROFIBUS DP networks.
• Provides built-in diagnostics for faster troubleshooting.
• Helps detect short circuits, communication errors, and signal reflections.
• Ensures better signal quality over long distances.

? Disadvantages:

• More expensive than a standard RS485 repeater.
• Limited to PROFIBUS DP networks, not suitable for general RS485 applications.

RS485 Repeater

? Advantages:

• Works with any RS485 protocol, including Modbus RTU and proprietary systems.
• Simple and cost-effective solution for extending RS485 communication.
• Available in many variations, including isolated and non-isolated versions.

? Disadvantages:

• Does not provide diagnostic features.
• Cannot segment networks intelligently like a PROFIBUS DP repeater.
• May not prevent issues such as bus failures or ground loops effectively.
• 4. When to Use Each?

Use Siemens Diagnostic Repeater if

• You are working with a PROFIBUS DP network.
• You need real-time diagnostics to identify faults.
• You want better network segmentation and signal integrity.

Use a Standard RS485 Repeater if

• You need to extend an RS485 communication network.
• The protocol is not PROFIBUS DP (e.g., Modbus RTU).
• Cost is a major concern, and diagnostics are not needed.

Case Study :

Setup

The setup consists of

? S7-400 with CPU Alternatively, a different CPU with DP interface and

integrated SFCs 58, 59 and 103 can also be used.

? PROFIBUS with Diagnostic Repeater 6ES7 972-0AB01-0XA0

? ET 200M with IM 6ES7 153-1AA02-0XB0

? ET 200M with IM 6ES7 151-1AA00-0AB0

The CPU is connected to interface DP1, the ET200M to interface DP2

and the ET200S to interface DP3 Diagnostic Repeater.

? A field PG for the engineering and for online functions of STEP 7 has

been connected at interface X1 (PG interface) of the Diagnostic

Repeater.

Description of the core functionality

The functionality has in this example been realized in 3 blocks, which are

described in the overview below.

Process sequence of main functionality

? FC 10 setting the clock of the Diagnostic Repeater

FC 10 reads the time from the CPU via SFC 1 READ_CLK and writes

this time to the Diagnostic Repeater with SFC 58 WR_REC.

This is initiated by the user via a trigger bit.

? FC 11 Topology determination

FC 11 triggers the topology determination for the DP master system via

SFC 103 DP_TOPOL; if several Diagnostic Repeaters are present in

one DP master system, then calling the SFC 103 addresses all

Diagnostic Repeaters of this DP master system. If the SFC 103

terminates the job with a temporary error, FC 11 performs a reset of

SFC 103 and triggers the topology determination again, for as long as

the given number of repetitions has not been reached.

The topology determination is initiated by the user via a trigger bit.

? FB 99 Reading diagnostic data from the Diagnostic Repeater

Reading diagnostic data from the Diagnostic Repeater is the main task

of this application.

The Diagnostic Repeater provides:

– Data for bus topology, which consist of PROFIBUS addresses of the

nodes and of relative station distances to the Diagnostic Repeater.

– One diagnostic buffer each for segments DP1, DP2, DP3 and PG

interface, which stores the last 10 events with time and date.

– Two statistic buffers for segments DP2 and DP3, in which

information on reflection and message frame fault rate are stored

with time and date.

FB 99 (with subordinate FB 100) reads the topology table, diagnostic

buffer and statistic buffer from the Diagnostic Repeater with the SFC 59

RD_REC; data are read successively in form of 12 data records. If the

SFC 59 terminates a job with a temporary error, then FC 100 triggers a

renewed reading, for as long as the given number of repetitions has not

been reached.

Reading the diagnostic data is initiated by the user via a trigger bit.

Reference:

1- https://support.automation.siemens.com/WW/view/en/7915183

2- https://support.automation.siemens.com/WW/view/en/1214574

3- https://support.automation.siemens.com/WW/view/en/21043574

4- https://support.automation.siemens.com/WW/view/en/23328167

5- https://support.automation.siemens.com/WW/view/en/10805964/130000

6- https://support.automation.siemens.com/WW/view/en/10805945/130000

Mostafa Sayed