Frequency radar sensors

All modern ACC radar sensors make use of the Fourier transformation for signal processing. Viewed in a simple manner, the Fourier transformation is a calculation-intensive transformation from the time domain to the frequency domain and reverse. A series of measured values defined in frequency steps, the frequency spectrum, is derived from a series of defined time steps. Modern signal... 

Fig. 7.7.6 24 GHz short-range radar sensor. The high frequency cir-...

Each sensor of the radar network has an individual position behind the front bumper. Therefore, each sensor will calculate individual values for target range and velocity based on the four measured beat frequencies, equation 8, inside the FMCW waveform. The measurement result is described by an eight-element parameter vector. 

Microwave switches are beam-breaker-type point sensors with an accuracy of 13 mm (0.5 in.) and with pressure and temperature ratings up to 28 bar (400 psig) and 300°C (600°F). Pulse-type radar gauges have ranges up to 200 m (650 ft) and are accurate to 0.5% FS, whereas frequency-modulated carrier wave (FMCW) units have errors from 1 to 3 mm (0.04-0.125 in.). Their pressure and temperature ratings are up to 80 bar (1,200 psig) and up to 400°C (750°F). 

The setup shown uses discrete radio-frequency components. The pC and the signal processing is integrated on the board. The pulse width of the 24 GHz radar is 300 ps. Some technical data of the sensor are as follows. 

Some ceramics are transparent to light of specific frequencies. These optical ceramics are used as windows for infrared and ultraviolet sensors and in radar installations. However, optical ceramics are not as widely used as glass materials in applications in which visible light must be transmitted. An electro-optic ceramic such as lead lanthanum zirconate titanate is a material whose ability to transmit light is altered by an applied voltage. These electro-optic materials are used in color filters and protective goggles, as well as in memory-storage devices. 

Only for particular molecules, e.g. ammonia because of its strong lines in the 20-40 GHz region, or water at 22 GHz because there is no other line until 183 GHz, would spectral considerations force the worker to lower frequencies. The 20-40 GHz band is also attractive, however, because of the cheap sources and low-noise semiconductor detectors, manufactured for movement sensors and short-path wireless links. The projected automobile collision-avoidance radar systems will make cheaper sources and detectors available for the 60-70 GHz region within the next few years. The 60 GHz across-office circuits for wireless data links could provide useful narrow-band sources for oxygen determination. The 35 GHz and 94 GHz close-range radar bands provide a useful reservoir of components and sources for the potential manufacturer of MMW spectrometers. 

This should be carried out, where practicable, using wetted process conditions to operate the sensor. Where this is not practicable then a simulated test of the sensor (eg radar, vibronics or radio frequency admittance) may be acceptable where it can be demonstrated that the wetted contact cannot be prevented from operating the sensor on genuine high-level condition. 

Another type of level measurement makes use of radar or microwave signals. In this case the sensor is located at the top of the vessel in which the Uquid height should be measured. A sensor outputs a frequency-modulated signal from 0-200 Hz. The signal that is reflected by the liquid surface is delayed in proportion to the distance between the level and the surface. 

According to Eq. 1, the shorter the wavelength, the higher the sensitivity of the measurement for a Ku radar, with wavelength X = 1.76 cm (operating frequency = 17 GHz), a phase variation of 1°, typically achievable using a state-of-the-art sensor, corresponds to a displacement of 20 pm. 

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