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Entry type: FAQ Entry ID: 109474533, Entry date: 05/27/2015
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With PROFINET IO via WLAN how do you set the update time and F-monitoring time in STEP 7 V5.x?

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This entry demonstrates how to set the update time and F-monitoring time with PROFINET IO via WLAN.

PROFINET IO can also be run via Industrial WLAN. However, WLAN cannot provide the 100 Mbit/s full duplex transmission rates required by PROFINET. If multiple WLAN clients are logged on to one access point, they share the maximum data rate. The transmission rate per WLAN client drops. Because of this and the roaming between the access points you have to change the following PROFINET parameters for WLAN:

  • Update time
  • F-monitoring time with fail-safe communication

STEP 7 sets the update time by default to a small value, 2ms, for example. With PROFINET via WLAN you should change the update time to at least 64ms in order to enable stable operation.

The minimal update time, which are maximal possible, you find in the document "Industrial Wireless LANs in a PROFINET IO Environment" under IWLAN: Setup of a Wireless LAN in the Industrial Environment.

Setting the update time in STEP 7 V5.x
Follow the instructions below to change the update time in STEP 7 V5.x.

  1. In the Hardware Configuration you click the PROFINET IO system. The "Properties" dialog of the PROFINET IO system opens.
   
Fig. 01
 
  1. Go to the "Update Time" tab.
  2. In the "Mode" column you set the "Fixed update time" mode.
  3. Change the update time.

     
    Fig. 02
     

Test to see if operation is stable and further increase the update time if the IO devices fail often.

Note

  • With PROFIsafe via WLAN you must also change the F-monitoring time. The F-monitoring time should be set to six-fold the update time. A detailied calculation you find in this entry 25412441 .
  • A fail-safe S7 connection via WLAN needs an even higher F-monitoring time. Set at least 2s.
  • The Safety-OB, e.g. OB35, must have a higher value as the PROFINET update time.

Setting the F-monitoring time in STEP 7 V5.x
Follow the instructions below to change the F-monitoring time in STEP 7 V5.x.

  1. Open the Hardware Configuration and double-click the F-DI or F-DO module for which you want to change the F-monitoring time. The "Properties" dialog of the F-DI or F-DO module opens.
  2. Go to the "Parameters" tab.
  3. Under "Parameters > F-parameters > F-monitoring time (ms)" you enter the required F-monitoring time.
     

    Fig. 03

Further Information
Entry ID 109475919provides information about how to set the update time and F-monitoring time in the TIA Portal.
Entry ID 92649989provides information about the configuration of a SIEMENS access point and a SIEMENS client.


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