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Page 226 MultiRanger 100/200 – INSTRUCTION MANUAL 7ML19981FB05
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Appendix B: T
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Distance Calculation
To calculate the transducer to material level (object) distance, the transmission medium
(atmosphere) sound velocity (P653) 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 Operation P001, Units P005, Volume Conversion,
P050 to P054, Reading, P060 to P063, OCM, P600 to P611, and/or Totalizer P622 to P633
parameters).
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 MultiRanger 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 Milltronics
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 (submerged in the liquid) in combination with an ultrasonic /
temperature transducer. Set Temp Source (P660) for both, 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 by performing a Sound
Velocity Calibration (P651) if the atmosphere is homogeneous (well mixed), at a fixed
temperature, and under consistent vapor pressure.
The MultiRanger 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 Velocity (P653) 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 Velocity (P653) may be entered directly.