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Metrology, standardization and certification |Метрология, стандартизация и сертификация

Lesson 1

Read the text: The goniometric indicator

 In a specific arrangement, by means of time constant of an RC circuit, a generator can generate a frequency which corresponds to a desired nominal speed. The outputs respectively block the output impulses appearing at the outputs of the generator. These impulses control power stages consisting of current-amplifying components which excite the drive coils in a bridge circuit. Because these drive coils lie in the magnetic flux, a rotation of the rotor by one pair of poles occurs. After this the permanent magnet has an opposite polarity with reference to the goniometric indicator, so that the described process is repeated, displaced in phase electrically through 180.degree.. This sequence is continued up to the frequency which corresponds to the RC combination.

If by chance the goniometric indicator is located in a neutral zone between north and south pole of the rotor magnet, no position detection occurs. In this case the arrangement may be such that the output of the comparison circuit excites the starter coil because no polarity exists at the outputs of the voltage comparators. The current flux in the starter coil leads to a rotation of the rotor magnet with reference to the goniometric indicator, so that the latter scan assume its control function. After starting, the comparison circuit is taken out of operation and the starter coil assumes the function of a tachogenerator. The generated voltage U2 is a direct-current measured quantity for the speed and now serves as a correction control quantity for a comparator stage regulating the rotor speed, which regulates the modulation time for the power stage of the drive coils in a correcting sense through a pulse width modulation.

If the operating voltages should not remain constant, for example where vehicle batteries in a varying state of charge are used, a comparator may be provided to compare the operating voltage with an internal reference voltage. If the operating voltage falls below a predetermined value, then the generator is switched off. It is switched on again only when the operating voltage exceeds a preselected value. The ratio between switch-off and switch-on process is a switching hysteresis.

The motor may be such that comparatively high forces and torques occur and so it may be necessary to anchor the stator windings firmly in the stator housing. This may be done in a particularly simple manner by using a coil support in the form of a compression moulding or injection molding, in which the flat windings of the drive coils and also the starter coil are arranged in the same general plane and are fixed by encasing with a suitable plastics material. The production process of a stator becomes particularly simple if the packing of the support and the encasing of the coils is effected simultaneously in a single work stage.

In order to ensure adequate cooling of the components of the electronic regulating and control device without appreciably widening the unit, the components of the electronic control or communication system may be arranged within the housing which may be cooled, on the rear wall of a common support plate of the electric motor and the compressor. In this way the individual components are bathed in a flow of cooling medium contained in the housing. The arrangement of the electronic components within the housing has the further advantage that only two electrical connections need be provided in the housing.

For compressors of small dimensions the so-called dead space between the piston end in the TDC position and the associated cylinder end face has a considerable influence upon the power behaviour of the compressor. In order to reduce this dead space, a spring plate of an admission valve may be made circular and with a diameter corresponding to the cylinder diameter. In this way it fills the entire surface in the cylinder head during compression and acts virtually as a continuous boundary surface of the cylinder chamber. It is particularly convenient to attach this spring plate to a valve seat plate by means of a hollow rivet, because then the interior space of the hollow rivet can serve simultaneously as a discharge orifice. A further reduction of the dead space can also be achieved if a corresponding recess for the head of the hollow rivet is provided in the piston end.

1. Match the left part with the right:

2. Complete the sentences with the suggested words: cylinder, valve, dead, surface

In order to reduce this _______ space, a spring plate of an admission _______ may be made circular and with a diameter corresponding to the _______ diameter. In this way it fills the entire _______ in the cylinder head during compression and acts virtually as a continuous boundary surface of the cylinder chamber.