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FMCW Radar |
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Reflex VG7 26Ghz Radar level transmitter
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Frequency Modulated Continuous Wave Operating Principle The VG7 High frequency (26 GHz) Radar operates on the same proven principle of the earlier lower frequency 10 GHz FMCW Radars. A radar signal is emitted via an antenna, reflected by the target level and received after delay time ‘t’ The high frequency signal (~26GHz) increases linearly by 2GHz during the measurement (frequency sweep) (1). The signal is emitted, reflected from the target surface and then received at a time-delayed frequency (2). The difference Df, is calculated from the actual transmitted frequency and the received frequency (3). This difference is directly proportional to the distance measured The frequency difference is processed via a Fast Fourier Transformation (FFT) into a lower frequency spectrum and the actual distance / tank level is calculated from this spectrum. Compared to the earlier 10 GHz units the main technical advantages are: Stable, crystal-controlled high transmit frequency of 26 GHz and a larger bandwidth of 2 GHz a Dynamic range more than 100 dB. |
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Digital signal processing provides very
high computing capacity. Complex evaluation algorithms ensure reliable
and precise calculation of measured values. The high average transmit frequency of 26 GHz provides better concentration and focus of the microwave signals, for improved accuracy, stability, and sensitivity, of the measured value. The large 2 GHz bandwidth makes it easier to distinguish between wanted and unwanted signals, and measured values are evaluated with greater accuracy. A dynamic range of more than 100 dB is attained using the FMCW principle. This determines the ratio between the strongest valid signals and the weakest possible signals in the form of fundamental noise. The unique Tank Bottom Following (TBF) mode enables products with low dielectric constants to be measured. For tanks with complex internal structures the Empty Tank Spectrum (ETS) can damp out all unwanted reflections from in tank obstructions. |
Advantages of FMCW principle compared to Pulse Radar Better reflection separation Reliable noise reduction Smaller beam angle Fewer disturbing reflections
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Key Benefits
Non-contact level measurement up to 40 metres (80 metres in special cases) Integral display of Level, Distance or Volume. High accuracy +/- 3mm Small blanking zone 2 wire loop powered 24vdc 4-20mA output. Optional all stainless steel construction Hazardous area ATEX Eex ia certification. HART, Profibus (PA) and Foundation Field bus. Suitable for narrow tanks with minimum fixed beam diameter. Unaffected by pressure, temperature, humidity, viscosity, foam or dust .Simple to install. Suitable for Aggressive liquids, hydrocarbons, toxic liquids and slurries. Granulated material and most solids.High temperature and pressure options are available. Remote or local programming, all tank parameters are held in local memory. Suitable for detecting levels through surface foam. Sealed Flange system allows electronics head removal under process conditions. TBF mode available for low dielectric products ETS mode damps out unwanted reflections |
Enhanced accuracy The difference in dynamic range between the best pulsed systems and the VG7 is more than 30 dB. This is equivalent in signal power to a sensitivity that is 1000 times greater. The larger dynamic range of the VG7 allows, for example, more stable detection of liquids with very low dielectric and thus very weak reflections. Between an dielectric of 2 and a dielectric of 1.2, in an otherwise identical measurement environment, the difference in level is approximately 11.5 dB, which is equivalent to 14 times the power difference on a linear scale. Given a large reserve in the dynamic range, as in the VG7, measuring accuracy will remain high even when signals are very weak, whereas in systems with a small dynamic range measuring accuracy will decline rapidly when signals are weak. |
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