Endress+Hauser Levelflex FMP51 Operating Instructions Manual page 46

Mounting
46
Requirements
• The dielectric constant of the medium must be at least DC > 7.
• The tank wall must be non-conductvie.
• Maximum wall thickness (a):
– Plastic: < 15 mm (0.6")
– Glass: < 10 mm (0.4")
• There may be no metallic reinforcements fixed to the tank.
Mounting conditions:
• The probe must be mounted directly to the tank wall (no open space)
• A plastic half pipe with a diameter of approx. 200 mm (8"), or some other protective unit, must
be affixed externally to the probe to prevent any influences on the measurement.
• If the tank diameter is less than 300 mm (12"):
A metallic grounding sheet must be installed at the opposite side of the tank. The sheet must be
conductively connected to the process connection and cover about the half of the vessel's
circumference.
• If the tank diameter exceeds 300 mm (12"):
A metal sheet with a diameter of at least 200 mm (8") must be mounted to the probe at the
process connection. Its orientation must be perpendicular to the probe (see above).
Calibration for external probe mounting
If the probe is mounted externally at the wall of the tank, the speed of signal propagation will be
reduced. There are two possibilities to compensate for this effect.
Compensation with the gas phase compensation factor
The effect of the dielectric wall can be compared to the effect of a dielectric gas phase. Thus it can
be compensated for in the same manner. The compensation factor if given by the quotient of the
actual probe length LN and the probe length meausred when the tank is empty.
The device looks for the end of probe signal in the subtracted curve. Thus, the value of the
measured probe length depends on the mapping. In order to obtain an exact value, it is
advisable to determine the probe length manually using the envelope curve display in
FieldCare.
Step Parameter
Expert ® Sensor ® Gas phase compensation ® GPC mode
1
Expert ® Sensor ® Gas phase compensation ® Constant GPC
2
factor
Compensation via the calibration parameters
If an acutal gas phase has to be compensated for, the gas phase compensation functionality is no
longer available for a correction of the external mounting. In this case the calibration parameters
(Empty calibration and Full calibration) must be adjusted and a value longer than the actual
probe length has to be entered into the Present probe length parameter. The correction factor
for these three parameters is given by the quotient of the probe length measured when the tank is
empty and the acutal probe length LN.
The device looks for the end of probe signal in the subtracted curve. Thus, the value of the
measured probe length depends on the mapping. In order to obtain an exact value, it is
advisable to determine the probe length manually using the envelope curve display in
FieldCare.
Step Parameter
Setup ® Empty calibration
1
Setup ® Full calibration
2
Levelflex FMP51, FMP52, FMP54
Action
Select Constant GPC factor option.
Enter quotient: "(Actual probe length)/
(Measured probe length)".
Action
Increase parameter value by "(Measured probe
length)/(Actual probe length)".
Increase parameter value by "(Measured probe
length)/(Actual probe length)".
Endress+Hauser