Where is all the wireless process instrumentation?
In researching an article on wireless developments for our October issue, I had occasion to review the offerings available under the WirelessHART and ISA100.11a protocols, and the lists of devices available under both were pretty short. While there have been commitments from various vendors to work with one or the other of these protocols, the number of actual “native” wireless devices available for either can be counted on one’s fingers.
Looking at the lists, let’s be clear as to what qualifies. Both protocols have an assortment of infrastructure devices, such as gateways and transmitter adapters that can be added to conventional wired devices. But, actual sensors that communicate via radio are harder to find. Some companies that have substantial instrumentation lines have no wireless devices at all. Why aren’t there more?
The article will go into greater detail as to some of the larger issues, but here are some things to think about:
The manufacturers’ assumption seems to be that wireless instrumentation, by definition, must be totally self-contained and battery operated. If you expand that notion to include a requirement that battery life has to be measured in years, those devices need to use power very sparingly. That eliminates devices that need high power levels (relatively speaking) such as a Coriolis flowmeter.
Sensors also have to be capable of turning on and rendering a stable reading within a few milliseconds. That eliminates something like a thermal mass flowmeter. Even devices that use low-power sensors need to reconsider how that sensor is managed. The challenge in a wired world is to make sure it will function with only 4 mA. Intermittent operation with rapid sleep/wake cycles is a whole different matter. Ultimately it means that you can’t just stick a radio module in your conventional wired products.
The result is that most of the wireless devices available now are toward the simple end of the spectrum.
So, if you’re serious about trying to make a substantial wireless deployment, you will need to use those wireless adapters with conventional wired devices, at least for the time being. The result will be instrumentation with a wired power connection, but no physical connection back to the control system.
Instrumentation suppliers are keen on expanding the offerings, and more suppliers will eventually come into the pool. For the moment, manufacturers are sticking with one or the other of the two main standards, however that division is likely to break down before too long. While making the jump from wired to wireless is pretty big, having both WirelessHART and ISA100.11a should be simpler, like the difference between Foundation fieldbus and Profibus PA.
Peter Welander, firstname.lastname@example.org