Siemens SIMATIC NET PROFIBUS, Owner'S Manual, Page: 40 / 490

Topologies of SIMATIC NET PROFIBUS Networks
2-14
PROFIBUS Networks SIMATIC NET
6GK1970-5CA20-0AA1 Release 2 05/2000
2.3 Topologies of Wireless Networks
Infrared Link Module (ILM)
In SIMATIC NET, wireless PROFIBUS networks are implemented with the “Infrared
Link Module (ILM)”.
Figure 2-8 PROFIBUS ILM
Maximum Length of a Link
Regardless of the transmission rate, the maximum length of a link is 15 m. The
infrared light used for data transmission is radiated at an angle of +/- 10
o
around
the mid axis. This means that at a distance of 11 m, an ILM illuminates a circular
area with a diameter of 4 m. The communication partner must be within this
illuminated area. There must be an uninterrupted line-of-sight path between both
ILMs. The ILMs are suitable for transmission rates of 9.6 Kbps to 1.5 Mbps.
Point-to-Point Link
To implement a point-to-point link, two ILMs are positioned opposite each other so
that each is located within the infrared light cone of the other. The maximum
distance between two modules is 15 m.