Levelflex FMP51, FMP52, FMP54
42 Endress+Hauser
Limitations for coax/rod probes
Maximum probe length LN • For rod probes:
LN ≤ 4 000 mm (157 in)
• For coax probes:
LN ≤ 6 000 mm (236 in)
Minimum probe length LN LN > L
ref
+ 200 mm (L
ref
+ 7.7")
Reference distance L
ref
300 mm (11.8") or 550 mm (21.7"), see feature 540 of the product
structure
Maximum level relative to sealing
surface of flange
L
ref
+ 150 mm (L
ref
+ 6")
Minimum dielectric constant of the
medium
DC > 7
Area of application
Level measurements with high pressure for measuring ranges up to a few meters in polar media with
a dielectric constant DC > 7 (e.g. water or ammonia), which would cause a high measuring error
without the compensation.
The accuracy of measurement at reference conditions is the higher the larger the reference length
L
ref
and the samller the measuring range:
5
10
15
20
25
30
35
40
45
0 500 1000 1500 2000 2500 3000 3500 4000
D [mm]
Delta [mm]
Lref = 550 mm
Lref = 300 mm
A0014535
D Distance from liquid surface to lower edge of the flange
Delta Measuring error
If there are fast changes in pressure, there may be an additional error, since the mesured reference
distance is filtered with the time constant of the level measurement. In addition, conditions of
imbalance - for example due to heating - may cause density gradients within the medium and
condensation of steam at the probe. As a result, the level readings at different locations inside the
tank may vary slightly. Caused by this application influences the measuring error may be increased
by a factor up to 2 to 3.
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