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Comms Loss: Wireless Connection Between S7-200 Client / Server

Created by: horsman at: 4/28/2008 8:49 PM (7 Replies)

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4/28/2008 8:49 PM	Rate (0)
horsman Posts: 27 Rating: (1)	I am having periodic communications loss between my S7-200 client and server which are connected over a wirless connection and I don't where I should be looking. I am using a W788-Pro as the access point and a W744 as the client module. I have the client CPU connected to the Access point and the server CPU to the client wireless module. It works fine most of the time but every once and a while I lose communication. Communication will usually re-establish within about three seconds but I can't tolerate any loss while my machine is running. I am using wireless instead of a slip-ring. The access point and the client are only about 6ft apart. I have the keep-alive on the CP243 set to the default 30s. Should I change this? What else should I be looking at? I have attached a log file for the access point. At 23:26 the connection drops then re-connects and then drops and re-connects again a few seconds later. Any input would be greatly appreciated. Thanks. Attachment Log File.zip (427 Downloads)
horsman Posts: 27 Rating: (1)
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4/28/2008 10:08 PM	Rate (0)
Krish Silver Member Joined: 5/24/2007 Last visit: 4/24/2024 Posts: 284 Rating: (27)	Hi Horsman I would be like to know more about the installation of the wireless.Is one of them moving? I am wondering if there is some interference asfrom the log it appears that the signal strength is dropping down and hence the loss of "IP Alive" signal response. This also means that you have cyclical data coming across the wireless. Try increasing the IP-Alive time or even disabling it and see if it is affecting the functions although I would not advise it for long time operation unless it is perfectly safe and non-mobile application. My guess is there is some interference in the path of the wireless link. So have a look at that. I can give some more thinking to it if you could briefly let us know the installation.

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4/29/2008 10:17 AM	Rate (0)
J_Bell Posts: 5822 Rating: (412)	Hello, I am sorry... but I wonder, do you use RCOAX asantenna? I would also check the signal strength of the Client in the AP, this could be done cyclically via the SNMP OPC to see if the signal strength is decreasing too much in a certain distance or at a certain point. If this is the case steps are necessary to change the installation there. Maybe another AP is interfering the signal... this would have to be investigated on site than. Best regards J_Bell
J_Bell Posts: 5822 Rating: (412)	Last edited by: J_Bell at: 4/29/2008 10:18 AM
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4/29/2008 11:29 AM	Rate (0)
INS Gold Member Joined: 4/6/2006 Last visit: 2/5/2024 Posts: 604 Rating: (56)	Hi, As every one mentioned I like to receive some more information about the total system. What standaard is selected? IEEE 802.1 a/b/g/h is the AP set to auto Channel? What Country is it installed (this because of the Country settings)? Which antenna is used? Is there a cable between AP/Client and antenne? What distance is between AP and Client? Can you place the log files of both devices? I see an overlap could it be that "Connect to any SSID"is enabled in the client? Is there a connection interrupt between the AP and the Client or between de S7-200 and the partner? This could be checked by the R1 LED on the client isf it's blinking green the WLAN connection is lost. Which FW is used? As J_Bell mentioned the signal strength of the Client would be interesting. Since FW:3.0 it's possible to get this directly out of the Webpage of the Client (744). Just jump to information >> signal and start recording. Please give us a printscreen from the graphic which is created.
	Best regards, INS
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4/29/2008 8:09 PM	Rate (0)
horsman Posts: 27 Rating: (1)	Hi Here some answers to your questions. I've answered as best I could for now. I'll have to get the signal strength and Client log to you later. However, the client is stationary and is only 6 ft away from the access point on a turn-table : What standaard is selected? It is set to IEEE 802.1 g is the AP set to auto Channel? Yes What Country is it installed (this because of the Country settings)? United States Which antenna is used? Just the standard antenna ANT795-4MR What distance is between AP and Client? 6ft Can you place the log files of both devices? I'll get them I see an overlap could it be that "Connect to any SSID"is enabled in the client? No. It is set to a specific SSID. Is there a connection interrupt between the AP and the Client or between de S7-200 and the partner? I'm not sure. Comms drop sporadically and I'm not there to see if R1 flashes. It comes back up seconds later. Which FW is used? I have to get this. Thanks
horsman Posts: 27 Rating: (1)
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4/29/2008 9:10 PM	Rate (0)
INS Gold Member Joined: 4/6/2006 Last visit: 2/5/2024 Posts: 604 Rating: (56)	Hi, And if possible it could be interesting to have a printscreen of the Overlap AP screen. Why did you choose the 802.11g? Did you scan for interferers? Have you enabled the option "Auto Channel Select"? Have you tried to switch over towards 5 GHz, IEEE802.11a? It's allowed to be used in the US and most of the cases there is less interference in that frequency range.
	Best regards, INS
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5/1/2008 7:08 PM	Rate (0)
horsman Posts: 27 Rating: (1)	Thanks INS, I will try 802.11a. It is set to "Auto Channel Select". I don't know very much about wireless communication so I will ask if it is to be expected that the system will be this sensitive to interference. I am a machine builder using this to replace slip-rings. I don't want to have my machine going down because someone sets up a wireless network next door or the microwave is on in the lunch room. Regards, Horsman
horsman Posts: 27 Rating: (1)
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5/1/2008 7:30 PM	Rate (0)
INS Gold Member Joined: 4/6/2006 Last visit: 2/5/2024 Posts: 604 Rating: (56)	Hello Horsman, It's not that tricky when you use Industrial WLAN as communication medium. It's more like other WLAN based solution like VoWLAN or the office network. In the most cases 2.4 GHz is used for these systems. But check the country regulations. It's possible to check easily since the list is inside the device. You can find it with your webbrowser: http://<<IP-Address>>/CountryList.log Viewing the list I have I would say use the channel 149/153/157/161/165 with the IEEE 802.11a. But I have to admit my list is not really up-to-date at the moment. The list is automaticly updated when you upgrade the firmware. Then you could check the range of the Access Point but in the US the Transmit Power Control (TPC) is enabled. This technology will enable the device to switch back to a lower power if possible (devices measures this) to gain less interference and to use less power. Just to be sure it is the easiest to first change the parameters on the Client and afterwards the AP. So you don't need to connect to the Client with a cable. After you changed parameters like a protocol (802.11a) or Channel you should look in the list of Overlap AP's it's inside the Access Point (W788-1PRO >> Information >> Overlap AP) it's the best to use a device without any overlap. And use the build-in Signal Recorder inside the client. Good luck!
	Best regards, INS
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