Siemens sitrans LU01 - Manual (Page 93)

7ML19985BE02 SITRANS LU01 – INSTRUCTION MANUAL Page 87
mm
mmm
Te
c
hnical Ref
e
re
nce
Variable air temperature is automatically compensated when a Siemens Milltronics
ultrasonic/temperature transducer is used. If the transducer(s) are exposed to direct
sunlight, use a sun shield or a separate TS-3 temperature sensor.
Also, if the temperature varies between the transducer face and the object monitored, a
TS-3 temperature sensor, mounted near the material surface (solids) or submerged
(liquids), should be used in combination with the ultrasonic/temperature transducer. Then
when Temp Source, (P660) is set for both, the transducer and TS-3 temperature
measurements are averaged.
Atmosphere composition other than air can pose a challenge for ultrasonic level
measurement. However, excellent results may be obtained if the atmosphere is
homogeneous, at a fixed temperature, and consistent vapour pressure, by performing a
Sound Velocity Calibration (P651).
The SITRANS LU01 automatic temperature compensation is based on the sound velocity/
temperature characteristics of air and may not be suitable for the atmosphere present. If
the atmosphere temperature is variable, frequent Sound Velocity Calibrations may be
required to maintain optimum measurement accuracy.
Sound Velocity calibration frequency may be determined with experience. If the sound
velocity in two vessels is always similar, future calibrations may be performed on one of
the vessels and the resultant Velocity (P653) entered directly for the other vessel.
If the sound velocity of a vessel atmosphere is found to be repeatable at specific
temperatures, a chart or curve may be developed. Then, rather than performing a Sound
Velocity Calibration each time the vessel temperature changes significantly, the
anticipated Velocity (P653) may be entered directly.
Volume Calculation
The SITRANS LU01 provides a variety of volume calculation features (P050 to P055).
If the vessel to be monitored does not match any of the 8 preset Tank Shape calculations,
a Universal Volume calculation may be used. Use the level/volume graph or chart
provided by the vessel fabricator (or create one based on the vessel dimensions).
From this graph, determine which Universal Volume calculation will provide the best
results, and select the level vs volume breakpoints to be entered (32 max.). Generally, the
more breakpoints entered, the greater the volume calculation accuracy.
Universal, Linear (P050 = 9)
level
volume