Wireless Webinar Q & A

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As promised, here are the questions and answers from yesterday’s webinar.  If you have a question that we did not get to, send us an email at webinarQ at PTOregistrations dot com.

Q:  If I want to use WLAN / WiFi with PROFINET, do I need special hardware like special access points?

No, you can use any IEEE 802.11 compliant access point. Of course you might want to look for ruggedized components or even IP65 or outdoor rated devices, depending on your environment. However, some of the industrial features like bandwidth reservation or redundant connections are only available in industrial access points.

Q:  Can I use the wireless card on my laptop with PROFINET?

 Absolutely!

Q:  Is the PROFINET protocol different on wireless? Do I need to look for a special “profile”?

No, nothing special is needed. PROFINET was built with wireless in mind. So the protocol is the same, whether it runs through cable or not.  This makes it easy to hook everything up.

Q: Are there any commercially available wireless I/O systems that employ wireless power supplies? I read about these in an IEEE publication…

We do not know of any current industrial solution which offers complete wireless power.  Some industrial providers of WLAN equipment offer a power over Ethernet (PoE) solution for your Wireless nodes (on the wired side) so you don’t have to supply them with mains power.  Zigbee products will also offer end nodes with such low power requirements that they can run off of simple batteries which can last years.  Please provide us with the IEEE publication which you are speaking of if you would like for us to dig into this further.

Q: Is the Bluetooth for industrial the same frequency and everything as our cell phones? This seems so unreliable with dropping out often.

No, if you mean the actual cell phone communications and not the headset to phone communications (Bluetooth).  And the Bluetooth headset is likely not what is ‘dropping out’, It’s probably your cellular provider.  If you refer back to the frequency table and Bluetooth section, Bluetooth uses the 2.4 GHz frequency band and Frequency Hopping / Adaptive Frequency Hopping to have a robust wireless signal immune to most interference.  Both WLAN and Bluetooth Wireless technologies will even employ retries when necessary to make sure the communications goes through.  Of course to make sure you won’t have drop outs or miscommunications it’s best to plan your wireless system in advance and make sure no obstacles exist and check out your ‘wireless’ paths. 

Q: Are wireless signals and devices immune to other noisy devices such as VFDs?

Only a site survey or tool for checking the system can tell you if there are problems with the wireless signals from noisy devices.  Interference from the kHz and MHz region such as arc welding, frequency inverters and switching operations won’t typically affect transmission for instance.  A drive would typically fall into this same category (kHz).

Q: What is the relationship between number of nodes and routing function delay in a mesh network?

There is not a hard and fast number for this.  The basic ZigBee routing function introduces delay from the way ZigBee router nodes (or the coordinator) handles the routing function.  And ZigBee uses a ‘tree routing’ method for routing information which is not an optimized routing method. 

Q: What is the approximate percent overhead for the ZigBee encryption methods?

There is not a hard and fast number for this either as ZigBee encryption can be handled in multiple ways and differently by each vendor. 

Q: Why use a proxy between PROFINET and a ZigBee network?

PROFINET is the application protocol and control network on Ethernet / WLAN above ZigBee and typically used for realtime and deterministic applications.  ZigBee is a simple bus for bit level types of information (sensors).  Having PROFINET in a ZigBee device is like putting a Ferrari engine in a Volkswagen body.  It just won’t work well.  So in order to implement PROFINET down to the ZigBee level you will want to use a proxy which acts as a PROFINET device on one side and ZigBee coordinator on the other to read back all of your sensor information to the PROFINET network. There are already proxies for PROFINET to go to many other networks like PROFIBUS, DeviceNet, AS-I, Interbus and others.

Q: What provisions exist for secure communication under ZigBee?

Please refer back to the webinar to the ZigBee security section. There are various ways manufacturers can implement security with ZigBee both from an encryption and an authentication aspect.  It again depends on the manufacturer as to what methods you have available.  You can also see a presentation about this at the ZigBee Alliance website online by searching on Google with the words ‘ZigBee Alliance Security’.

Q: Where would you get Sinema E for checking an area before wireless installation?

As this is a Siemens product, please contact your local Siemens Distributor if you are interested in Sinema E.

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