ABB has introduced a range of wireless proximity sensors that can be
installed at any location within a machine cell without cable
connections. Signals to and from the sensors are relayed in full duplex
mode using the company's new WISA (wireless interface for sensor and
actuators) protocol via a special input module that connects to the
machine control system. This input module can accept signals from up to
120 proximity sensors at a time and can be connected to any major
fieldbus system, using ABB's Fieldbus Plug technology.
Meanwhile, power to the sensor electronics is provided by an
electromagnetic induction loop system, installed along the boundary edges
of the machine cell. Small coils within the sensor housing are
subsequently able to generate the 6mW of power required by the sensor
electronics.
To protect against loss of signal, the sensor can simultaneously receive
both strong and weak signals, even where a large interfering signal may
exist at an adjacent frequency. Added protection against signal
deterioration is also afforded by the swapping of the transmission and
reception antennas at the input module, which ensure that there is always
a path for the signal.
At present there are four different sensor head sizes available (flush or
non-flush mounting), covering switching distances from 1.5 to 15mm. The
units are IP67 protected and will operate over the temperature range of
-25 to +55oC.