When commissioning a PROFIBUS Installation it is advisable to proceed according to the following steps:
Step 4.1 Check installed cable
If an appropriate test protocol of the installation is available, this step may be omitted (see step 3.4).
We check whether all plugs have been connected correctly and whether cable screening has been applied everywhere. The bus connection may only be switched on at both ends of the cable. We can use one of the following test methods:
•measure cable with an Ohmmeter
•check test signal on cable with ScopeWare
Step 4.2 Check addresses assigned and station accessibility
We switch on the supply to all field devices and check whether the addresses have been set correctly and so allow stations to be accessed. The following methods of measurement may be used:
•We have a development environment with an on-line live list, such as STEP7. We check whether all connected stations are listed in this live list.
•We use a bus monitor like, for example, ProfiTrace and have it display the live list for us. We check whether the right devices are indeed on the address provided.
Step 4.3 Check correct configuration and parameters of stations
If the configuration and initial parameters are consistent, all field devices will indicate an active connection with the master (normally a green LED) and the controller will show no further faults. With a bus monitor like ProfiTrace, it is possible to determine the status of connected field devices from their green colour on the live list.
Please note: If signals on the field device are in a disallowed state, the field device can sent a diagnostic message. This is often signalled in the controller and/or field device with a red diagnostic LED. However, this does not mean that the PROFIBUS is not working properly! With ProfiTrace the presence of a pending diagnostic message is indicated by a small red spot.
Step 4.4 Check transmission quality
If a PROFIBUS installation functions without displaying any error LEDS, this does not necessarily mean fault-free operation (refer also to Technical article). We can carry out more exact measurements with a bus monitor like ProfiTrace:
•How long is the current cycle time of PROFIBUS-DP?
•How often are telegrams repeated by the controller?