Varec 7532, Installation And Operation Manual

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7532 Appendix
11.4 Function and system design
11.4.1 Measuring principle
The 7500 RTG is a "downward-looking" measuring system, operating based on the
time-of-flight method. It measures the distance from the reference point (process
connection) to the product surface. Radar impulses are emitted by an antenna, reflected
off the product surface and received again by the radar system.
Input
The reflected radar impulses are received by the antenna and transmitted into the
electronics. A microprocessor evaluates the signal and identifies the level echo caused
by the reflection of the radar impulse at the product surface. The unambiguous signal
identification is accomplished by the PulseMaster® software based on many years of
experience with time-of-flight technology. The mm-accuracy of the 7500 RTG is
achieved with the patented algorithms of the PhaseMaster® software.
The distance D to the product surface is proportional to the travel time t of the impulse:
D = c · t/2,
with c being the speed of light.
Based on the known empty distance E, the level L is calculated:
L = E – D
Reference point for "E" is the lower surface of the process connection.
The 7500 RTG is equipped with functions to suppress interference echoes. The user can
activate these functions. They ensure that interference echoes (e.g. from edges and weld
seams) are not interpreted as level echo.
L0
0-F
M
R5
3xxx-1
5-00
-00
-e
n-0
01