The Right Technology for the Application
Many proximity devices are on the market, using many technologies. Most of these devices perform simple tasks such as turning on lights, opening doors, selecting menu options, etc. RFID devices are also sometimes used. And, some have adapted RFID sensors, both passive and active types, for the purpose of keeping pedestrians from getting hit by vehicles.
In work environments there is a great need for ways to automatically protect pedestrians from being hit by vehicles or machines, to prevent machines from colliding with each other, and to keep pedestrians and machines from dangerous areas. Since there are so many proximity devices available, including RFID sensors of numerous types, one might conclude that these devices should be the solution to keeping safety in the work environments involving mobile machines and vehicles.
Methodical System Engineering shows that using these simplistic devices will not satisfy the safety need.
Consider the essential, basic performance requirements for a proximity safety system in an industrial setting:
1. Establish precise boundaries between safe and unsafe zones
2. Reliably warn both pedestrians and operators if there is potential danger
3. Provide means to signal a vehicle to slow down or stop
4. Do not produce nuisance alarms
5. Compact packaging to easily be integrated into a vehicle and/or to be carried
The first requirement above essentially eliminates most types of proximity devices, including RFID. The only known method of producing boundaries around vehicles, with the desired precision and stability, is to produce magnetic fields. Low frequency magnetic fields can be produced that are of a precise size and do not easily change their shape when other objects are placed within their range. Shaped fields are effective for creating types of hazardous or safe zones.
This cannot be said, for example, for RFID devices that emit electromagnetic fields that are either blocked or attenuated by most materials. Even the human body will attenuate RFID emissions so that when measured after passing through a person’s body, the field strength is measurably less than if unimpeded by the body. Magnetic fields remain unchanged in size and shape by persons or objects placed between their source and the point of measurement. Even metallic objects usually have little effect, especially when compared with RF transmissions, because the magnetic field is in the shape of a solid ellipsoid and goes around the objects rather than having to pass though objects to reach the point of measurement.