Technical reference
A.7 Sound velocity
HydroRanger 200 HMI
306
Operating Instructions, 06/2018, A5E36281317-AC
A.7
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 device 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 (submerged in the liquid) in combination with an
ultrasonic/temperature transducer. Set Temperature source (2.11.1.4.) (Page 219) 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
1)
if the atmosphere is
●
homogenous (well-mixed)
●
at a fixed temperature
●
under constant vapor pressure
The device 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
2)
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
2)
may be entered directly.
1)
Auto sound velocity (2.11.1.8.) (Page 221)
2)
Summary of Contents for HydroRanger 200 HMI
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