A Real Time Location System (RTLS) has been a wonderful idea for a long time, but it also has been pretty expensive for a long time. So I’ve developed an alternative solution that may get you 90% of the benefit at 10% of the cost.
The problem is that you need to install a large amount of fixed infrastructure to track a few number of (relatively) slow moving parts. This simply is not cost effective. The ROI for RFID is strongly correlated with the density of RFID tags to be read. So for a fixed reader, we would like the readers installed where many parts are moving by them.
Traditional RTLS solutions require either:
- Active RFID tags with batteries (that go dead)
- An array of fixed antennas in all the areas where you may want to find parts
- Or both of the above!
RTLS uses triangulation methods, where the signal from the active tag is received by 3 or more antennas and then some pretty heavy-duty calculations carried on to figure out where in 3D space that tag and the asset it is attached to is actually located. The RTLS system prefers line-of-sight for simpler calculations, but with sophisticated systems they can also take into account the time delays if the signal is bounced once or twice before reaching the antenna and still give a pretty good answer. Unless, of course, something changes! Opening the large metal shipping door changes the characteristics of if, and where, the signal bounces. With enough time (and money) this situation can be modeled and added into the calculation mix, but it ain’t cheap.
An alternative is to use inexpensive, passive RFID tags and portable (handheld) readers to record approximately where you are when your RFID reader last saw that part. This can be accomplished by defining a special filter bit in an EPC Gen2 data structure to represent a “Location Tag”. But let’s not talk in theory but give you a working application.
In GS1/EPC Tag Data Standard, the Aerospace & Defense Indicator (ADI) format defines up to 64 different filter bits as well as larger EPC data fields to contain the actual ‘social security number’ (manufacturer and actual Serial Number of the item, written in ASCII) of the part to be identified and tracked. One of those filter bits (24) is designated for “Location Tags”.
One large airline has every aircraft in their fleet tagged with one of these Location Tags containing the Tail Number (and other information) of the airplane it is installed on. When a handheld reader comes aboard the aircraft to scan other parts (life vests under seats, etc.), the airline’s application is also is looking for a Location Tag and then it knows exactly which aircraft it is scanning, without worrying about human typos being made on the little keyboard. Because the passive tags only read from a 20’ distance, there is no chance that the Location Tag from the plane next door is going to be read.
Would this be useful in your operations? More examples of this “poor man’s RTLS solution will be shared in a later blog.