FI71621C - Speed sensor. - Google Patents

Description

1 71621

The rotation sensor

TECHNICAL FIELD The present invention relates to measuring instruments and in particular to speed sensors.

Technical background

The basic requirement for measuring instruments and sensors is the accuracy of the measurements. The design of the sensors and the principle of the measurements are chosen so that the output is not affected by interfering factors or noise.

Conventionally, the speed sensors each comprise a permanent magnet, which is a disc with alternating, radially or axially magnetized poles and a central opening for the shaft and a winding mounted on a base made of insulating material. The number of active conductors is equal to (2n + 1) p, where n is an integer, p is the number of poles. These active conductors are placed opposite the poles of the permanent magnet and connected in series at the ends of the windings (cf., for example, 20 GB application 2 022 326, filed 31.5.1979, class H 02 K 11/00, 16/04, 21/00, G 01 P 3/48, and U.S. Patent 4,093,897, Class H 02 P 5/06). The winding is connected to a compensating circuit for series connection in these prior art devices to eliminate an interference signal that contributes to the error in determining the rotational speed. For the same purpose, the winding of the sensor is divided into several blocks, each transferred 180 degrees and connected in series (cf., for example, L.N. Safonov, V.N. Volniansky et al., Pretsizionnye 30 Datchiki Ugla s Pechatnymi Obmotkami, Precision Printed-

Winding Angle-Data Transducers. Biblioteka Priborostroitelia, 1977, Mashinostroenie Pubi., Moscow, pp. 7-13, 58-60).

When the permanent magnet rotates the useful signal smv with varying polarity, the winding is induced in the active conductors. But at the same time, external magnetic or electromagnetic fields induce 2,71621 noise smv in the active conductors and winding leading ends. These fields are compensated in the active conductors of the winding because they are connected in series with the opposite series, while they are summed at the ends of the windings because the front ends of the windings are connected in series via the active conductors.

In summary, noise signals are not completely canceled in prior art speed sensors because the compensating rotation of the winding is located at some distance 10 from the ends of the windings due to the inherent structure of the winding itself. This is especially significant when the external electromagnetic field is not symmetrical, such as that produced by the mains transformer. In such sensors, noises induced in the conductors between the winding and subsequent equipment are also not compensated.

DESCRIPTION OF THE INVENTION It is an object of the present invention to provide a speed sensor in which the complete reversal of external noise contributes to a more accurate determination of the rotational speed.

A speed sensor is provided comprising a permanent magnet, which is a disc having alternating poles around its circumference and a central opening for the shaft and a winding placed on a mounting base, the active conductors of the winding being located opposite the permanent magnet poles and connected in series with the winding ends. comprises an additional winding, the active conductors and front ends of which connect said active conductors in series, arranged in the same way as the active conductors and front ends of the main winding, very close to each other and with 30-330 degrees of electrical transmission, and a differential amplifier with inputs connected to the main and auxiliary windings joi-35 hink connectors while their other connectors are connected to a common differential amplifier supply line.

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Preferably, the differential amplifier in the tachometer should be made as a voltage comparator.

The speed sensor according to the invention allows a very accurate determination of the rotational speed from the complete reversal of the electromagnetic noise of the lead-5 support.

BRIEF DESCRIPTION OF THE DRAWINGS The present invention will now be described with reference to a particular embodiment thereof in conjunction with the accompanying drawings, in which:

Figure 1 shows an overview of a speed sensor according to the invention;

Fig. 2 shows a section taken along the line II-II in Fig. 1, according to the invention; Figure 3 shows an enlarged view of a base part made of an insulating material with windings arranged in the slots of said base according to the invention;

Fig. 4 schematically shows the view of Fig. 3 if the directions of the electromagnetic noise pattern are shown according to the invention;

Figure 5 shows an electrical circuit diagram of a winding and a voltage comparator according to the invention;

Figure 6 shows the electrical input and output signals of a voltage comparator according to the invention.

The best way to practice the invention

The speed sensor comprises a permanent magnet (Figures 1 and 2) with a plate having radially magnetized N- and S-poles alternately along its circumference. The Le-30 has a central opening 2 for fitting the shaft 3. The sensor also comprises windings 4a and 4b placed in the slots 5 of the base 6 in this embodiment (Fig. 3), which base is made of an insulating material. The windings 4a and 4b consist of active conductors 7a and 7b 35 connected in series with the winding heads 8a and 8b. These active conductors 7a and 7b are arranged opposite the poles of the permanent magnet 1 71621 (Fig. 2) very close to each other in the same slots. The winding ends 8a (Fig. 3) and 8b are located very close to each other, respectively. The windings 4a and 4b are offset from each other by an angle 5 in the range of 30 to 330 degrees of electricity. These limits are derived from the allowable level of the output signal. In this sensor embodiment, the windings 4a (Fig. 4) and 4b are shifted by 180 electrical degrees or 1t / p, where p is the number of poles. In this case, such a transfer is thought to be optimal.

The speed sensor also comprises a differential amplifier 9 (Fig. 1), the inputs of which are connected to the same terminals of the windings 4a and 4b, while the other terminals of the windings 4a and 4b are connected to the common line 10 of the differential amplifier 9. The same terminals are either the tail ends.

The voltage comparator 11 (Fig. 5) is used as a differential amplifier to provide a rectangular output signal of the sensor.

In another embodiment of the speed sensor, an axially magnetized permanent magnet is used. Here, the active conductors of the windings are arranged in the same way as in the sensor described above, but in the radial direction.

25 Double-sided printed circuit boards can be used to make sensor windings.

The speed sensor manufactured according to the invention operates as follows.

As the permanent magnet 1 rotates (Figs. 1 and 2), the signal 30112 (Fig. 6) is induced in the winding 4a (Fig. 5) connected to the inverting input of the comparator 11. The frequency of this signal 12 is a function of the speed of rotation of the sensor. The signal 3 induced in the winding 4b has the same frequency and amplitude, but is in a different phase 35 compared to the signal 12. The amplified rectangular signal 14 is produced at the output of the comparator 11.

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In the case where the sensor is exposed to an external electromagnetic noise field, the noise smv £ * is induced in the active conductors 7a (Fig. 4) and 7b, and in the end ends 8a and 8b of the winding. The noise smvs are canceled out by the active conductors 7a and 7b, which are connected in series, while they add up to the ends 8a and 8b of the winding. In addition, the smvs are deposited on the signals 12 (Fig. 6) and 13 generated and summed by the rotating magnet and applied as smv to the inputs of the comparator 11 (Fig. 5). Since the noise signal is applied to the inputs of the comparator in Sara phase, it has no effect on the output signal 14 (Fig. 6).

In summary, the effect of external electromagnetic fields can be almost completely reversed by implementing two identical windings, the active conductors of which are offset by an angle in the range of 30-330 degrees and placed very close to each other, such as the ends of the windings, and using a voltage the windings are connected. Noise cancellation makes it possible to improve the accuracy of the speed measurement.

Industrial suitability

The invention is mainly applicable to electric motors used in video and audio recording and reproducing apparatus for measuring and controlling the rotational speed of such motors.

Claims (2)

6 71621 A speed sensor comprising a permanent magnet having a plate with alternating poles arranged along its circumference and a central opening for shaft fitting, and a winding mounted on a base, the active conductors of the winding being arranged opposite the poles of the permanent magnet and connected in series with the winding ends, characterized by that it comprises 10 additional windings (4b), the active conductors (7b) and the winding ends (8b) of which form a series connection with said active conductors (7b) being arranged in the same way as the active conductors (7a) of the main winding (4a) ) and the winding ends (8a) very close to each other and shifted in the range of 30 to 330 degrees of electricity, and a differential amplifier (9) having inputs connected to some terminals of the main and auxiliary windings (4a and 4b) with their other terminals connected to said differential amplifier ( 9) to the common feed-20 feed line (10). Speed sensor according to Claim 1, characterized in that the differential amplifier is designed as a voltage comparator (11). Il