Contactless Inductive Revolution Marker

A. V. Murin

(Presented by the scientific seminar of the Department of Applied Mechanics)

During investigations of machines it is often necessary to measure the speeds of rotating links. When it is necessary to record them by means of a loop oscillograph, tachogenerators of various types are usually used as speed sensors. In those cases where tachogenerators are very difficult or impossible to use, measurement of the rotational speeds of links with sufficiently high accuracy can be carried out by means of contactless magnetoelectric revolution markers. When measuring the speeds of rotating links with revolution markers, as is known, the oscillograph film records the electrical pulses generated by these sensors once per revolution, or over part of a revolution of the link, and the time marks provided by the time marker. From these data one can quite simply determine the average speed of the rotating element over a period of time corresponding to 2–3 revolutions or to a fraction of a revolution.

In known designs of contactless inductive revolution markers [1; 2], a permanent magnet is used to create the magnetic flux. The need to use a sufficiently strong permanent magnet of special design greatly complicates, or in some cases makes impossible, the use of such revolution markers (large dimensions of the sensor, manufacturing complexity, it is not always possible to avoid amplification of the output signal, etc.).

In connection with the need to carry out investigations, under production conditions, of the rotational speeds of the links of the drives of a multi-motor overhead conveyor, and with the impossibility of using other methods and devices for this purpose, we developed and successfully used a very simple contactless inductive revolution marker, free of the shortcomings indicated above.

Figure 1 shows the arrangement of the developed revolution marker. In the device under consideration, instead of a permanent magnet an electromagnet is used, which made it possible to simplify the design of the core and reduce its dimensions. As a result, the coil with a U-shaped laminated core, mounted stationary on the machine bed, has not one winding (as is done in known devices of this type), but two windings: a primary and a secondary. The primary winding of the coil is supplied through a potentiometer with purely direct current (having only a DC component) and thus serves as...

to create a magnetic flux in its core. The secondary winding of the sensor coil is connected to the vibrator of an oscillograph. The use of a potentiometer makes it possible to vary, over wide limits, the magnitude of the current in the primary winding and thereby to change the level of the output signal very simply and smoothly.

The moving part of the marker being described—the armature, as can be seen from the figure—may be a plate 0.5–1.5 mm thick made of ordinary low-carbon steel. In order to reduce the gap between the armature and the core and, consequently, to increase the level of the output signal (if necessary), the armature should have the form of an arc of a circle with a radius equal to the distance by which it is removed from the axis of rotation of the link. This armature plate is mounted on the rotating link in such a way that, when passing by the sensor core at a distance of 0.5–1.5 mm, it can simultaneously cover both of its poles. It is obvious that the armature, passing by the core and thereby reducing the air gap between its poles (as shown in Fig. 1, a), changes its magnetic reluctance, and this, in turn, leads to a change in the magnetic flux and to the induction, as a result, in the secondary winding of the coil of an emf, the pulse of which is recorded on the oscillograph film. Naturally, if it is necessary to determine the change in speed of the rotating link within one revolution, the armature must be made in the form of a toothed disk.

Fig. 1. Diagram of the device of a contactless induction revolution marker

With the connection scheme for the secondary winding of the marker coil as shown in Fig. 1, a, the recording of emf pulses on the oscillograph film will be arranged on both sides of the zero line. If it is necessary to obtain a record of revolution marks only on one side of the zero line, a diode should be inserted into the circuit of the secondary winding, as shown in Fig. 1, b.

In comparison with known devices, the developed revolution marker has a number of obvious advantages: there is no permanent magnet and, as a result, the design and manufacture of the device have been simplified; the dimensions are considerably smaller; the emf pulse is large and can easily be varied over wide limits by changing the supply voltage of the primary winding with the aid of a potentiometer, etc. The level of the output signal of the revolution marker under consideration is such that, with comparatively small dimensions (core cross section—6 × 7.5 mm; number of turns of the primary winding—2000, and of the secondary—1000, wound with PEV-2 wire, diamet-

…with a gap of 0.14 mm and a supply voltage of about 3 V, it is possible to record it on the oscilloscope film even with the aid of a type II vibrator.

The use of the developed contactless inductive revolution marker in investigations under factory conditions has shown its high reliability and exceptionally good operation. This fact, as well as the above-mentioned advantages of this revolution marker over known ones, allow us to recommend it for measuring rotational speeds or the speeds of translational motion of links in cases where it is impossible, or very difficult, to use other methods for this purpose.

References

1. N. P. Raevskii. Methods for the Experimental Investigation of Mechanical Parameters of Machines. Publishing House of the Academy of Sciences of the USSR, 1952.

2. N. P. Raevskii. Sensors of Mechanical Parameters of Machines. Publishing House of the Academy of Sciences of the USSR, 1959.