8
4.4 Special information on DNV-GL approval
For use under DNV-GL conditions (if device approval is available), observe
the following instructions:
• Single probes and coaxial probes up to a length of 500 mm can be
operated without support�
• For probe lengths from 500 mm to 2000 mm, coaxial probes must be
used� These must be supported additionally, either at half length or at
the end� The support must be suited to damp occurring vibrations�
• If using a coaxial pipe with a length of 700 mm or longer, additional
centering pieces must be mounted in this coaxial pipe (→ Accessories).
5 Function
5.1 Measuring principle
fig. 5-1
fig. 5-2
D
The unit operates to the principle of guided wave radar� It measures the level
using electromagnetic pulses in the nanosecond range�
The pulses are transmitted by the sensor head and guided along the rod
(fig� 5-1)� When they hit the medium to be detected they are reflected and guided
back to the sensor (fig� 5-2)� The time between transmitting and receiving the
pulse directly relates to the travelled distance (D) and the current level� The
reference for distance measurement is the lower edge of the process connection�
The figures show the operation with single probe� In case of operation with
a coaxial probe, the guided wave runs only along the inside of the coaxial
pipe�
