Now that wireless technologies have taken their place in everyday life, they are also beginning to establish themselves in the area of automation technology. However, due to the special interfaces and communications technologies, as well as the still frequently employed PLC, this is taking some time.
With the Dataeagle Series from Schildknecht Elektronik, wireless data systems are available to solve a variety of problems, depending on the frequency band and bus system in question.
Naturally, wireless data is nothing new in the field of automation technology. Solutions that permit digital and analog data to be transmitted over greater or lesser distances have been on the market for years. In the meantime, wireless modems with serial interfaces are also available. Due to the limited bandwidth of these bands - often referred to as narrow-band transmission - the technical limitations of such devices only allow transmission paths with low data rates to be established. As a rule, 19 200 Baud or, in individual cases, 38 400 Baud, can be achieved. While these bands are still more or less suitable for the transmission of several bits, one quickly runs up against the limits if an attempt is made to transmit software protocols from industrial controllers via these interfaces.
Data security?
In general, radio is a so-called 'shared medium' with no rights to exclusive use. So, in day-to-day operations, a wireless data system must be capable of securely detecting faults, delays, as well as the loss of data packets and, if necessary, correcting these problems. Yet many of the wireless modems available in the market have either no, or only a very simple data protection layer on the wireless side. Today, however, the use of broadband wireless systems makes bands available that demand a standardised wireless protocol (2,4 GHz: 802.11b protocol; 1,9 GHz: DECT protocol) with a data protection layer.
The Dataeagle units also operate on these standards. Compared with narrow-band wireless systems with 25 kHz at 433/869 MHz, the larger bandwidth up to 20 MHz permits a significantly higher data transmission rate (1 to 11 MBps). It serves to protect the data along the transmission path.
Adverse conditions
Broadband wireless systems are, however, still viewed with some scepticism. On the one hand, the negative influences from other 2,4 GHz systems such as microwave ovens, nursery monitors, wireless LAN, and Bluetooth are frequently cited. On the other, fog is said to limit the range. In principle, these influences apply to all wireless systems. While microwave ovens certainly do raise the general background noise to a limited extent, good and stable data transmission is nonetheless possible at distances as close as 20 cm to these interference generators.
Beyond a spatial distance of 5 m, no influence is detectable. In addition, and in contrast to narrow-band transmission, binding wireless protocols for broadband applications exist to regulate common operation. At 433/869 MHz any hacker can permanently block any wireless transmissions on this band with a cheap noise generator. Using broadband, on the other hand, Dataeagle units, WLAN, and Bluetooth can operate side-by-side in a wireless cell. The applicable rules then provide each subscriber with time-offset access, thus giving each a 'clear run'.
© Technews Publishing (Pty) Ltd | All Rights Reserved
printer friendly version