GB2349475A

GB2349475A - Sensor to non-contactingly measure the rotation of a rotor in a liquid flowmeter

Info

Publication number: GB2349475A
Application number: GB0007897A
Authority: GB
Inventors: Thomas Haar
Original assignee: Alfons Haar Maschinenbau GmbH and Co KG
Current assignee: Alfons Haar Maschinenbau GmbH and Co KG
Priority date: 1999-04-12
Filing date: 2000-03-31
Publication date: 2000-11-01
Anticipated expiration: 2020-03-31
Also published as: DE29906448U1; DE10012315B4; GB0007897D0; DE10012315A1; GB2349475B; FR2792067B1; FR2792067A1

Abstract

A sensor (24) to non-contactingly measure the rotation of a rotor in a liquid flowmeter wherein the rotor (10) is supported in a housing (16) having at least one recess (22) for accommodating an electromagnetic coil (26), which is driven at resonance, and the impedance of which is periodically changed by an electromagnetic interaction with the rotor (10) when it rotates. A counting apparatus counts the number of changes per unit time. The rotor (10) contains at least one ferromagnetic insert (18). The housing (16) is made up of a non-magnetisable metallic conductive material at least in the area of the recess (22). The recess (22) has a thin bottom facing the interior of the housing. The frequency of the resonance circuitry has been chosen so that a significant attenuation of the resonance in the coil (26) takes place upon the passing of the insert (18).

Description

A( 2349475 1 SENSOR TO NON-CONTACTINGLY MEASURE THE ROTATION OF A ROTOR IN

A LIQUID FLOWMETER The invention relates to a sensor to non-contactingly measure the rotation of a rotor in a liquid flowmeter according to the preamble of claim 1.

Flowmeters ftequently operate with armatures rotationally driven according to the principle of displacement. For example, the rotor accommodates wings disposed in radial recesses which sealingly cooperate with a cavity in the housing. A lateral sealing towards the housing provides for the whole liquid volume to help rotate the rotor, and prevents the occurrence of short-circuits. The flow rate may be determined by counting the revolutions of the rotor.

It is known to determine the rotational ftequency by leading a shaft of the rotor to the outside and measuring the rotation of the shaft in an optical manner or by structured metallic disks, for example, which cooperate with an electromagnetic coil. The coil, when approached to metallic conductive regions, will change its attenuation or impedance because of the eddy currents generated in the metal. When A -2the coil is driven by resonance a mistune will occur by the change in impedance so that such changes may be counted.

It is also known to move a sensor provided with an electromagnetic coil or a plurality of sensors towards the rotor through holes in the cover of the flowmeter casing and to determine the rotation of the rotor from the existence of different eddy effects. The measuring frequency of such measuring methods ranges between 100 kHz and 10 mHz. Such relatively high frequencies provide for the safe detection of conductive materials because of the high skin effect in a manner largely independent of their conductivity. Moreover, very high counting rates will be possible when such pulse generators are employed.

The drawback of the solutions described is that a physical connection exists between the measuring chamber in which the rotor runs in the housing and the region outside the measuring chamber. Such a connection needs to be secured by given minimal gaps and a series of sealings, which is expensive and susceptible to trouble. In addition, there is a problem in explosion-proof installations. For example, when flowmeters measure combustible or explosive liquids and the measuring coils are driven by a voltage, on the other hand, there will be some difficulty of meeting the requirements for explosion-prooffiess as imposed by authorities.

It is the object of the invention to create a sensor to rion-contactingly measure the rotation d' a rotor in liquid flowmeters wherein a direct connection may become unnecessary between the measuring chamber and the exterior region.

This object is achieved by the features of claim 1.

According to the invention, the rotor is provided with at least one ferromagnetic insert and the sensor is accommodated in a hole of the housing wall which is closed towards the interior of the housing. Located in the hole is the electromagnetic coil which preferably is driven by resonance, but there is no connection to the measuring chamber. The material of the housing comprises a material which is conductive, but is not ferromagnetic, at least in the area ofthe hole. The bottom is relatively thin, preferably smaller than 1.5 mm in thickness.

The inventive sensor, which operates as an inductive pulse generator, permits to measure the rotational motion of the metallic rotor through a metallic casing. When the measuring frequency chosen is relatively low and ranges from 8 to 30 kHz, for example, the magnetic field generated by the coil is capable of penetrating the bottom of the hole because of the reduced skin effect. This presupposes that the housing material has no marked ferromagnetic properties at least in the area of the hole. Thus, the magnetic field of the coil is acted on by the ferromagnetic insert, which leads to a corresponding attenuation on the coil. The eddy currents provoked in the metallic rotor which, in turn, will have the consequence of a magnetic field are small. Hence, approaching the ferromagnetic insert to the coil will result in a distinct change to the coil impedance.

As mentioned earlier, the coil preferably forms part of a resonant oscillating circuit. The oscillating circuit has been tuned in view of the permanent eddy losses occurring in the housing and will only be determined by an approach of the magnetisable insert located on the rotor. Thus, the sensor is preponderantly sensitive to magnetic materials behind a magnetic partition.

As was shown the inventive sensor, therefore, makes it no longer necessary to provide a connection between the measuring chamber and the exterior of the measuring chamber.

The hole for accommodating the at least one sensor is preferably located in the front-side cover of the housing. The arrangement of such a sensor in the housing cover is known per s6.

The invention will now be described in detail by way of an embodiment shown in the drawings.

Fig. I shows a side view of a rotor of a flowmeter which is known as such.

Fig. 2 shows a section through a portion of the rotor of Fig. 1 and the cover which closes the housing which, for the rest, is not shown in detail.

In Fig. 1, there is shown schematically a rotor or armature 1.0 for a flowmeter known as such, which has four recesses 12 disposed at uniform circumferential spacings to accommodate wings or blades defining, along with a chamber (not shown) of a housing (not shown), a measuring chamber through which a liquid flows while causing the rotor 10 to rotate via the wings. Thus, the axis of rotation is perpendicular to the plane of the drawing. In Fig. 2, which shows a partial section through the rotor of Fig. I and that of the housing, it can be seen that rotor 10 is pivotally supported in a cover 16 of the housing by means of an anti-friction bearing 14. It is understood that rotor 10 is also supported correspondingly at the opposite front face of the housing.

Recesses 18 at the front side of rotor 10 have inserted in them circular or cylindrical inserts 20 of magnetisable material at uniform circumferential spacings. The outer surface of inserts 20 is flush with the front side of rotor 10, which only defines a minimal gap with cover 16.

Pocket holes 22 are formed from outside in cover 16 on a circle which is concentric with the axis of rotation of rotor 10. The number of pocket holes 22 may correspond to the number of inserts 20, but may also be smaller. The divided circle for holes 22 corresponds to the divided circle for the inserts 18.

Disposed in each hole 22 is an inductive sensor 24 which has an electromagnetic coil 26, which is driven by resonance from a circuitry (not shown). Coil 26 is mounted in or on a pin 28, which is inserted in hole 22 and is closed at the outer end by a cap 30 which sealingly bears against the outer surface of cover 16. The remaining circuitry components for an oscillating circuit are also mounted on or in the pin, but may also have their places outside the housing. In any case, an electric connection requires to be created from outside to the coil, at least one for voltage generation.

Cover 16 is made of a conductive material as is rotor 10. However, it is made from a non-ferromagnetic material such that the electromagnetic coil 26 will generate eddy currents in cover 16 and in rotor 10 as well. The effect of the fields of such eddy currents on the field of coil 26, however, is relatively low as compared to the interaction between the coil 26 and the ferromagnetic inserts 20.

The frequency by which coils 26 are driven is relatively low, ranging approximat ely between 8 and 30 kHz. Therefore, the electromagnetic field is capable of penetrating the relatively thin bottom of pocket hole 22, which is 1.5 mm or less, and of getting in an interaction with.inserts 20.

Claims

1. A sensor to non-contactingly measure the rotation of a rotor in a liquid flowmeter wherein the rotor is supported in a housing having at least one hole for accommodating an electromagnetic coil, which is driven approximately by resonance by means of a circuitry and the impedance of which is periodically changed by an electromagnetic interaction with the rotor when it rotates, and has a counting apparatus counting the number of changes per unit time, characterised in that the rotor (10) contains at least one ferromagnetic. insert (20), the housing is made of a nonmagnetisable metallic conductive material at least in the area of the hole (22), the hole (22) is a pocket hole having a thin bottom facing the interior of the housing, and the frequency of the oscillating circuit has been chosen so that a significant attenuation on the coil (26) substantially takes place only by the passage of insert (20).

2. The sensor according to claim 1, characterised in that the bottom is of a maximum thickness of 1.5 mm.

3. The sensor according to claim I or 2, characterised in that the hole (22) is disposed in the fi:ont-side cover of the housing.

4. The sensor according to claim I to 3, characterised in that the frequency of a coil (26) ranges between 8 and 30 kHz.

5. A sensor substantially as described with reference to the accompanying drawings.

6. A flowmeter including a sensor in accordance with any one of the preceding claims.