Wireless, self-powered pushbutton modules

When planning new industrial buildings and plants, intelligent automation solutions are becoming more and more popular, often employing several decentralised control units. However, the wiring of the necessary control elements quickly becomes expensive and inflexible.

Wireless pushbuttons, which do not require any cable, are an ideal solution for this problem. They need no wiring at all and allow very flexible handling and arrangement of the switches and pushbuttons. Conventional wireless pushbuttons, however, do have two major disadvantages:

• They use batteries to supply power, which must be changed regularly.
• Signal transmission takes relatively long (approximately 50 to 70 milliseconds), which may result in an overlapping of two switching operations so that one of the two signals gets lost.

One way out of this dilemma is the use of the innovative wireless transmission technology from EnOcean. This technology provides the required activation energy from actuation and ambient energy. This disposable energy is generated as kinetic energy eg, during switching operations or vibrations, or even as thermal energy eg, by light radiation or temperature differentials.
This technology, therefore, allows operation of control units without cable connection and even without batteries, thus making the units wireless, self-powered and low-maintenance.

New wireless transmitter modules from Schlegel use this technology for battery free transmission of a pushbutton signal. In this case the required energy is produced by the switching operation itself, thus making it independent from ambient conditions.

Transmission of the radio signal takes place on the licence-free SRD band (short range devices) at 868 MHz with a transmission power of 10 mW. Three very short telegrams are sent within 25 ms, including an individual 32-bit ID, the polarity of the supply voltage and the actual payload (one to two input signals).
The transmitted signals can be processed by all receiver modules that recognise the EnOcean wireless standards, provided they have been programmed for the specificity of these pushbuttons, which is already implemented eg, in the four-channel relay modules and the radio receiver of WAGO’s I/O system.

The transmission range is up to 300 m in a free field, but strongly depends on the surrounding materials and the position of other energy generators or metal surfaces. Hence, certain basic conditions have to be observed for the installation planning, such as eg a minimum distance of the receiver to other transmitters or high-frequency sources of interference. A field intensity meter allows users to determine the optimal positions for sender and receiver.
The wireless pushbutton module from Schlegel is available in two designs. Type DMF_A can be used as a contact element for all two-position pushbuttons and two-position selector or key switches, while model DMF_B is available for three-position selector or key switches.

These modules have been designed to be combined with the actuators of the DUX-Basic control unit series. The module DMF_A, however, can be used for all suitable Schlegel ranges.
The size of the modules is approximately 43 x 45 x 29 mm. They function at temperatures between -40°C and +65°C and comply with the R and TTE-EU standards for radio equipment.

(Source dataweek.co.za, 06.08.2008)