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Automotive HandBook BOSCH

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Description

Analog signals are electrical quantities whose amplitude, frequency and phase convey information on physical variables or technical processes. Data registration is continuous in both time and quantity; within certain limits, analog signals can reflect any number of quantitative variations at any given point in time.

Analog technology provides means for processing these signals. Initial processing, consisting of filtering and amplification, can be supplemented by mathematical operations such as addition and multiplication, as well as integrationover time, etc.

 The operational amplifier (OP) is an integrated circuit of extreme importance in analog technology. Under ideal conditions, a relatively simple external circuit is sufficient for determining its operating characteristics (infinite amplification, no input current).

Various physical factors can be employed to modify the intensity, phase (coherent laser light) and polarization of the light conducted in the optical fibers. Fiber-optic sensors are impervious to electromagnetic interference; they are, however, sensitive to physical pressure (intensity-modulation sensors), and, to some degree, to contamination and aging. Inexpensive plastic fibersare now available for application within some of the temperature ranges associated with automotive applications. These sensors require special couplers and plug connections.

Short-circuiting ring sensors consist of a laminated soft-magnetic core (straight/ curved U- or E-shape), a coil and a moving, highly-conductive short-circuiting ring made of copper or aluminum. When an AC voltage is applied at the coil, a current Iis created which is dependent on the inductance of the coil. The eddy currents thereby created in the short circuiting ring limit expansion of the magnetic flux to the area between the coil and the ring itself.

 The position of the short-circuiting ring influences the inductance and thus the coil current. The current Iis thus a measure of the position of the short circuiting ring. Virtually the entire length of thesensor can be utilized for measurement purposes.

The mass to be moved is very low. Contouring the distance between the sides influences the shape of the characteristic curve: Reducing the distance between the sides toward the end of the measuring range further enhances the good natural linearity. Operation is generally in the 5…50 kHz range, depending on material and shape.

The task of measuring various rotations of a rotating part (e.g. steering spindle) is solved with a dual configuration of “pseudo-Hall angle sensors”. Here the two associated permanent magnets are moved by the rotating part via a step-up gear train.

 However, as the two smaller driving gears differ to the tune of one tooth, their mutual phase angle is a clear measure of the absolute angular position. Each individual sensor also offers an indeterminate fineresolution of the angle of rotation.

 This configuration provides a resolution more precise than 1° for e.g. the entire steering-angle range of four full rotations

ACC systems (Adaptive Cruise Control) with just such a long-range radar sensor are vehicle-speed controllers with automatic detection of vehicles which are driving in front in a lane and where braking may be required. A working frequency of 76 GHz (wavelength approx. 3.8 mm) permits the compact design required for automotive applications.

 A Gunn oscillator (Gunn diode in the cavity resonator) feeds in parallel three adjacently arranged patch antennas which at the same time also serve to receive the reflected signals. A plastic lens (Fresnel) set in front focuses the transmitted beam, referred to the vehicle axle, horizontally at an angle of ± 5° and vertically at an angle of ± 1.5°.

 Due to the lateral offset of the antennas, their reception characteristic (6 dB width 4°) points in different directions. As well as the distance of vehicles driving in front and their relative speed, it is thus also possible to determine the direction under which they are detected.

Directional couplers separate transmitted and received reflection signals. Three downstream mixers transpose the received frequency down to virtually zero by admixing the transmit frequency (0…300 kHz). The low-frequency signals are digitized for further evaluation and subjected to a high-speed Fourier analysis to determine the frequency.

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