Dear Control Engineering: It’s been interesting following some of the problems that Apple is having with its iPhone 4. Should I be concerned about similar reception difficulties with wireless instrumentation devices?
It’s difficult to compare a cell phone network and wireless instrumentation in a typical industrial plant, but some of the issues of one may be instructive for another. Apple’s situation is indeed interesting. Reports suggest the antenna on the new model 4 isn’t nearly as effective as had been hoped, and part of the problem is that some claim the company’s engineers knew this all along and management released the device anyway. Moreover, there are reports that the phone displays higher signal strength than it should. (Full disclosure: My family has three of the older model 3 iPhones and we generally seem fairly satisfied.)
Cell phones are different than wireless instrumentation devices for many reasons. Here are a few:
First, the phone has an intelligent operator: you. When you make a call, you have the ability to choose where you do it. You can avoid areas where coverage is poor, and if you lose a call, it probably isn’t the end of the world.
Second, designers create antennas to be portable and small, not necessarily for the best reception. It has to fit into your pocket.
Third, cell phone networks have hugely elaborate infrastructure systems.
If you are evaluating wireless instrumentation, in most cases you’re probably considering either WirelessHART or ISA100.11a devices. In many respects these are very similar, at least insofar as radio propagation is concerned.
When creating wireless networks, you can survey your plant and determine how communication is likely to operate. This includes identifying interference sources, obstacles, etc. Since a wireless pressure sensor can’t move itself to a better location, it has to work where it is. You will place your gateways where they can do the most good.
While the device is bolted down, the network can change the way it communicates if necessary. Both systems have capabilities built in that allow a device to re-route itself if its primary path is obstructed.
Wireless devices do not have to fit into your pocket, so they can have more effective antennas. Specialized antennas can be added for specific types of applications where required.
While it might be amusing to watch Steve Jobs squirm through this situation, the problems that Apple is experiencing should not make you resist considering wireless instrumentation for appropriate applications. The potential upside is far too great. Read our story, The Transparency of Wireless for more detailed information.
–Peter Welander, [email protected]
Control Engineering
