Wireless standards like ZigBee and 802.11 enable “intelligent” sensor networks
By Lynn Linse, Industrial Specialist/Engineer, Digi International
For decades, the sensor market has been fairly static with the basic physical designs changing little.
Vendors are forced to innovate in the production process, squeezing small improvements in profit margin by reducing their production costs. For the end users, innovation has been largely in the devices that use sensors, with the exception being a few lower-cost sensor families that have improved in accuracy due to better production methods.
While this reduces final cost to end-users, it tends to squeeze the sensor vendor's profit margin further as cheaper sensors do the work of more expensive ones.
However, changes in market expectations and the growing acceptance of wireless sensors have opened up rich opportunities for multi-sensor products for end-users, as well as better profit margins for sensor vendors.
In the beginning, there was no such thing as sensors – one paid for a complete control system, and the things which did the sensing were components of that system.
Need a new temperature thingy? Order part number XYZ-123. Don’t like the price of part XYZ-123? Can’t buy part XYZ-123 anymore? Buy a new control system.
Then the common sensor standards evolved – things we take for granted today like RTD, thermocouple, and 4-20mA.
It helped solve the “find part XYZ-123 or die” syndrome, but to credit user demands with this change is naive. In truth, it was a win-win situation.
Users of course benefited from the common, interchangeable sensors, but the big system suppliers did not like the constant grind of designing, testing, stocking and selling custom sensors. It interfered with their ability to satisfy customers.
Yet the sensors are really just a means to an end. For example, what is more important: the details of the temperature sensor used, or how warm is your room?
Yesterday, the HVAC system owned the answer to “how warm is your room?” If you wanted access to that knowledge for non-HVAC purposes — to time house plant watering, to confirm that your pipes were not freezing, to automatically open/close drapes, etc. — then you had to pay the tens of thousands of dollars required to buy an HVAC gateway device — or you had to contract the HVAC vendor to add a plant-watering-advisory tool.
The trend we are seeing today, and tomorrow, is for the sensor data to become a utility distinct from the HVAC and higher control systems. Wireless standards like ZigBee and 802.11/WiFi are largely to blame for this change.
Take a new smart ZigBee-enabled room thermostat as an example. It serves its reason-to-be as it sends the knowledge of room temperature to the HVAC system, but it also allows other automation systems to know the room temperature directly.
The owners of the things-measured benefit from this trend, their needs (and imaginations) can run wild and free. HR departments can compare absenteeism with room temperature and humidity changes. Energy consultants can help rein in power used for lighting. Uncle George can see if his Minnesota basement is too cold from Florida.
We see a new generation of multi-sensor ‘utility’ boxes being offered. After all, adding large hardware cost to every simple sensor doesn’t add up. Why add $40 of cost to a temperature sensor, and another $40 of cost to a light sensor?
Instead, imagine a commercial room light-switch/thermostat ‘utility box’ which includes:
Light switch – people like to turn lights on and off as desired, yet the ‘system’ could turn off lights if the room is unoccupied. The power inherent in a light-switch also offers full-time power to the box.
Motion detection – sense if the room is occupied. Help employees find ‘open’ meeting rooms. Save energy by powering off the lights in empty rooms. Augment security by detecting intruders at 3 a.m.
Light sensors – sense if the lights are on and working. Sense how much ambient light is coming in the windows. Enable reduced lighting loads when it is light outside.
Temperature and humidity sensors – sense if the room is reasonably comfortable.
Warmer/Colder buttons – allow the occupants to temporarily ask for more heat or cool.
Adding $40 of ‘network’ overhead to this utility box breaks out as only $8 per function. Functioning as a ‘sensor utility’, this box could feed data into:
Who is driving this change?
Although users tend to like the idea of buying a multi-purpose sensor, it is largely driven by the sensor vendors trying to improve their bottom-line by moving up the product food-chain.
Selling a smart sensor at twice the price of a commodity one might triple or quadruple profits. The existence of wireless and wide-area-network partners allows a sensor vendor to offer a simple wireless sensor infrastructure which can move sensor data across any site — or across the globe.
One might expect the large HVAC suppliers to resist this trend, and of course some will … just as some big vendors resisted the change to standard sensors.
Yet in the end, they will benefit by off-loading the wasted R&D and support costs of making their systems unnaturally flexible. After all, an HVAC system should be designed to control heating, ventilation and air-conditioning systems – not help Human-Resource Departments manage worker absenteeism.
So if you are an end-user looking to add sensors to your assets, take a look at the newer, more open wireless standard products. If you are a sensor vendor, look into expanding your product line with wireless sensors which feed data up into Ethernet and IP-based data systems directly.
Lynn Linse is Industrial Specialist / Engineer for Digi International, www.digi.com. With more than 30 years data communications experience, Linse is an industry expert regarding wired and wireless networking from a simple sensor all the way up to cellular or satellite access to that sensor.