Siemens SITRANS LUT400, Operating Instructions Manual

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Page 264 SITRANS LUT400 (HART) – OPERATING INSTRUCTIONS A5E33329501
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App. A - T
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Distance Calculation
To calculate the transducer to material level (object) distance, the transmission medium
(atmosphere)
2.12.1.1. Sound Velocity
is multiplied by the acoustic transmission to
reception time period. This result is divided by 2 to calculate the one way distance.
Distance = Sound Velocity x Time / 2
The Reading displayed is the result of performing any additional modification to the
calculated distance as determined by:
•
2.1.2. Sensor Mode
,
•
2.1.1. Units
,
• Volume conversion parameters -
2.6. Volume
,
2.2.3. Sensor Offset
,
• Flow parameters -
2.15. Flow
,
• and/or Totalizer parameters -
2.16. Totalizers
.
Sound Velocity
The sound velocity of the transmission medium is affected by the type, temperature, and
vapor pressure of the gas or vapor present. As preset, the SITRANS LUT400 assumes the
vessel atmosphere is air at +20 °C (+68 °F). Unless altered, the sound velocity used for the
distance calculation is 344.1 m / s (1129 ft / s).
Variable air temperature is automatically compensated when a Siemens ultrasonic /
temperature transducer is used. If the transducer is exposed to direct sunlight, use a
sunshield or a separate TS-3 temperature sensor.
Also, if the temperature varies between the transducer face and the liquid monitored, use
a TS-3 temperature sensor in combination with an ultrasonic / temperature transducer.
The TS-3 must be installed as close to the material as possible to ensure best
performance. It is acceptable to submerge the TS-3 if necessary. Set
2.12.1.3. Temperature
Source
for Average of Sensors, to average the transducer and TS-3 measurements.
Atmosphere composition other than air can pose a challenge for ultrasonic level
measurement. However, excellent results may be obtained if the atmosphere is
homogeneous (well mixed), at a fixed temperature, and consistent vapour pressure, by
performing a
2.12.1.6. Auto Sound Velocity
.
The SITRANS LUT400 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, perform frequent sound velocity
calibrations to optimize measurement accuracy.
Sound velocity calibration frequency may be determined with experience. If the sound
velocity in two or more vessels is always similar, future calibrations may be performed on
one vessel and the resultant
2.12.1.1. Sound Velocity
entered directly for the other
vessel(s).
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
2.12.1.1. Sound Velocity
may be entered directly.