Appendix
Micropilot M FMR 231 with HART/4...20 mA
86
E Hauser
11.4
Function and system design
11.4.1
Function (Measuring principle)
The Micropilot 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.
L00-FMR2xxxx-15-00-00-en-001
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 Micropilot S could be achieved with the patented algorithms of
the PhaseMaster® software.
The distance D to the product surface is proportional to the time of flight 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
Refer to the above figure for the reference point for "E".
The Micropilot is equipped with functions to suppress interference echoes. The user
can activate these functions. They ensure that interference echoes (i.e. from edges and
weld seams) are not interpreted as level echo.
20 mA
100%
4 mA
0%
D
L
F
E
flange:
reference point of
measurement
flange:
reference point of
measurement
inactive
length
max.level
threaded
connection
1 ½”
(R 1
:
reference point of
measurement
BSPT
½”)
or 1½ NPT
