Radar Technology for Level Gauging - Krohne

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3. Radar-Füllstandsmesssysteme For air at normal conditions, the difference in the propagation rate compared to a vacuum is only 0.03%. For deviating pressures and temperatures the following graph is obtained: K Normalized propagation rate in air 1.000 0.999 0.998 0.997 0.996 0.995 0.994 0.993 0.992 0.991 0.990 temperature 150°C / 300°F 100°C / 210°F 150°C / 120°F 0.989 125°C / 75°F 0.988 110°C / 30°F 0.987 -25°C / -15°F 0 5 10 15 20 25 30 35 40 bar pressure 145 290 435 580 psi Significant deviations arise only when pressure levels exceed 10 bar (145 psi), the measuring error then exceeds 0.3%. A correction will of course only make sense provided the pressure in particular remains approximately constant during measurements. Oxygen, nitrogen and argon behave similarly to air; with other gaseous media the quantitative effect can, dependent on ε r, N be lower or even substantially higher: Medium εr, N - 1 Medium εr, N - 1 Helium 0.07 · 10 -3 Air 0.59 · 10-3 Hydrogen 0.26 · 10-3 Carbon dioxide 1.00 · 10-3 Oxygen 0.52 · 10-3 Hydrogen chloride 4.60 · 10-3 Argon 0.55 · 10-3 Ammonia 7.20 · 10-3 Nitrogen 0.58 · 10-3 Fig. 23: Change in propagation rate at pressure and temperature Radar handbook 29 6
6 Fig. 24: Change of propagation rate in the waveguide (K = c/c o) 3. Radar-Füllstandsmesssysteme 6.1.2 Propagation rate on lines Electromagnetic waves are propagated at the speed of light along a loss-free line (sections 4.4.1 to 4.4.4). When the line is completely surrounded by a dielectric ε r, or the coaxial cable is filled with a dielectric, the propagation rate is: Given a spatially restricted dielectric (e.g. planar line, section 4.4.3) or given ohmic and/or dielectric losses 20 ,value c/c 0 needs to be specially calculated. 6.1.3 Propagation rate in stillwells/waveguides Another physical factor affecting the propagation rate is when microwaves are propagated not in free space but inside a pipe acting in the same way as a waveguide (see chapter 4.4.5). The liquid surface to be measured is located inside the stillwell. 20 Heat loss in the conductor / dielectric material Correction factor for propagation rate in the waveguide diameter / wavelength D / 30 Radar handbook
Page 1 and 2: © KROHNE 07/2003 7.02337.22.00 GR
Page 3 and 4: Content page 1 Introduction 5 1.1 R
Page 5 and 6: Symbols used a Distance, spacing
Page 7 and 8: 2 2. General 2.1 Frequency, wavelen
Page 9 and 10: 2 3. Radar-Füllstandsmesssysteme 2
Page 11 and 12: 3 Fig. 3: Geometric configuration o
Page 13 and 14: 3 Fig. 5: Pulse radar measuring sys
Page 15 and 16: 3 Fig. 8: Basic circuit diagram of
Page 17 and 18: 4 4. Components for radar systems F
Page 21 and 22: 4 Fig. 14: Planar line 4.4.3 Planar
Page 23 and 24: 4 Fig. 17: Examples of planar direc
Page 25 and 26: 5 Fig. 20: Various form of antenna
Page 29: 6 6. Wave propagation 6.1 Propagati
Page 35 and 36: 6 6.5 Modified radar equation Based
Page 37 and 38: 6 Fig. 28: Arrangement to measure t
Page 39 and 40: 7 Fig. 31: Reflection factors of di
Page 43 and 44: 7 3. Radar-Füllstandsmesssysteme O
Page 45 and 46: 7 Fig. 35: Influence of the angle o
Page 51 and 52: 8 Fig. 39: Counting method to deter
Page 53 and 54: 8 Fig. 41: A high-pass filter and i
Page 55 and 56: 8 Fig. 44: Subtraction of empty-tan
Page 57 and 58: 8 Fig. 47: Principle of operation o
Page 59 and 60: A Annex A Table of dielectric permi
Page 61 and 62: B B System-theoretical comparison b
Page 63 and 64: B 3. Radar-Füllstandsmesssysteme T
Page 65: C 3. Radar-Füllstandsmesssysteme [

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