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Diagnostics tools for commissioning the PROFIBUS DPnetwork

QUESTION:What options to I have for diagnosing errors in the DP master system during the commissioning phase?

ANSWER:Errors can occur on the PROFIBUS DP network for the following reasons:

Bad wiring / installation of the bus cable

Incorrect configuration of the DP masters and the DP slave

Incorrect configuration of the associated PROFIBUS DP network

Incorrect addressing of the communication in the program of the CPU

In the following we will present the diagnostics tools available for the various error sources.

Bad Wiring/Installation of the Bus Cable

BT200 BUS TESTER

The BT200 Bus Tester is available for checking the wiring. The following tests can be made with the BT200 BusTester when the PROFIBUS cable is not in use:

Checking the PROFIBUS cable:

Wire breakage

Shield breakage

Short circuits between wires and between wire and shield

Location of breakage/short circuit of data cables

Recognition of reflections that are causing faults

Incorrect wiring

Length of wiring installed

You can also use the BT200 Bus Tester for diagnostics when the network is in use:

Checking the availability of slaves:

List of reachable slaves

Selective addressing of separate slaves

Checking the RS 485 interface of the master and slave:

RS 485 driver

Power supply for line termination

RTS signal

Display of the PROFIBUS DP address

SIGNAL LEVEL MEASURING WITH AN OSCILLOSCOPE

Using an oscilloscope you can display the signal level on the PROFIBUS. This should have a rectangular form. Aspecialist should be employed to evaluate the image.

Configuration of the DP Master and the DP Slave

To check the configuration of the DP master and the DP slaves connected to it you can monitor it in the HWConfiguration both offline and online. The configuration can be downloaded from the CPU for offline analysis.

If you analyze the configuration online in the HW Configuration, you can identify failed or defective modules. In thecase of modules that support diagnostics it is also possible to detect imminent channel faults (e.g. wire breakage).

Fig. 1: Online view of the HW Configuration

If modules fail, then the event is logged in the diagnostics buffer.

Fig. 2: Diagnosticsbuffer of a CPU withslave failure

PROFIBUS DPNetwork

Some PC interfacesfor PROFIBUSprovide you withdiagnostics. You canfind them via "SetPG/PC Interface" or"Set PC Station".

Here you can readout the actual busparameters and youare presented withan overview of thePROFIBUS nodesavailable.

Fig. 3: SIMATIC Netdiagnostics

AMPROLYZER

The Amprolyzer software is also available foranalyzing the PROFIBUS network with thefollowing functions.

Lifelist with all the PROFIBUS nodes on thebus

Overview diagnostics with the currentoperating states of the nodes

Bus statistics with the number of eventssuch as timeouts and message repetitions

Automatic detection of transfer rate

Message recording with trigger and filteroptions with respect to events andmessage content including time stamp

Storage and export of message records inExcel format

Information on the Amprolyzer product isavailable in Entry ID: 18818699.

Program of the CPU

A frequent source of error is also the STEP 7program designated for data communication.Incorrect I/O access (e.g. I/O access via T AW20) to nonexistent addresses can be easily detected via thediagnostics buffer of the CPU .

If system functions (e.g. SFC14/15) are used for data communication, then the success of data transfer can bedetermined via their return values. You can observe the return values via the variables table or the online view ofthe LAD/FBD/STL editor.

When using certain modules, extraordinary programming of accesses might be necessary. When using CP342-5,for example, it is not possible to access the I/O via load/transfer commands or system functions SFC14/15. Hereyou have to use special functions (FC1 "DP_SEND" and FC2 "DP_RECV"). But also in this case you candetermine success of data transfer from the return values of these functions via the variables table or the onlineview of the LAD/FBD/STL editor.

Note:Users of S7-SCL or CFC also have the option of online monitoring of return values.

More information on the procedure for troubleshooting is available in Entry ID: 19379085.