DE1951532A1 - Device for magnetic gas analysis - Google Patents

Description

HARTMANN & BRAUN Frankfurt, the lo. October 1969

Aktiengesellschaft Grafstrasse 97 ot / EO

Device for magnetic gas analysis

The invention relates to a device for magnetic Gas analysis, in particular for determining the oxygen content of a gas sample.

Magnetic gas analysis makes use of the property that has long been known that two substances are different magnetic susceptibility, which are exposed to the same inhomogeneous magnetic field, the substance with the greater susceptibility to places of greater density of force lines and the substance with the smaller susceptibility to places smaller force line density is driven. This method is suitable for gas analysis because some gases can have very different magnetic susceptibility; for example, oxygen is of the order of magnitude higher magnetic susceptibility than almost all other gases. So it is possible to unite in this way to create an analyzer that is specifically sensitive to oxygen. A corresponding arrangement for gas analysis can be the

German patent specification 9 ^ 7 · 932.

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In this arrangement there is a dumbbell-shaped displacement piece, which is preferably spherical at both ends Thickening carries, between the magnetic pole pieces of two U-shaped, opposing permanent magnets arranged. The pole pieces are shaped so .., da / 3 the magnetic field is inhomogeneous. The whole arrangement is in a gas mixture, from which the portion of a gas with a magnetic susceptibility different from the accompanying gases is to be determined. In the Measurement of oxygen is preferred to the oxygen molecules due to its large magnetic susceptibility at the points of denser magnetic lines of force and those made of non-magnetic material, for example made of glass, displace existing end pieces of the dumbbell from these points. The deflection angle is if the dumbbell is mounted, for example, in the middle against a restoring force, a measure of the volume fraction of the relevant Gas.

The cited patent also shows that that it is known about the dumbbell-shaped displacement body to lay a wire loop consisting of one piece and lead out the connections on the bearings. It is then possible, for example with the help of a mirror attached to the dumbbell body, which is illuminated by a light source and throws the light on a photocell, one of the

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steering to generate proportional current that, if necessary returned to the wire frame after reinforcement, counteracts the deflection and compensates for it. The each for Compensation required current is then a measure of the volume fraction of the gas to be measured.

The disadvantage of such a device is that the on The mirror attached to the dumbbell must be illuminated from the outside, which causes difficulties when the whole arrangement must be in a gas-tight housing. Also, the amount of energy reflected back must be precisely adjusted Photocell are captured, the output of which is then fed to an amplifier.

The invention has the task of scanning the deflection and the current required for compensation on a purely electrical basis Make or generate ways and should in particular an oxygen concentration measuring device with fully automatic compensation and provide high accuracy.

The invention is based on a device for magnetic Gas analysis, especially to determine the oxygen content of a gas sample, with one between the poles an inhomogeneous magnetic field located deflectable displacement system with non-magnetic end pieces and with one, the twisting system surrounding, of one, the

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Deflection proportional current flowing through wire frame, whereby the magnetic field generated by the current counteracts the deflection in automatic compensation. The invention is that an oscillator fed, fixed Excitation coil system and a receiver coil system are provided and that the coupling of the two systems via the wire frame assigned to the displacement system takes place.

In a further advantageous embodiment of the invention are the non-magnetic ones located between the magnetic poles End pieces of the displacement system from the wire frame in the horizontal plane equatorial, i.e. perpendicular to the Magnetic lines, while the remaining part of the displacement system consists of a perpendicular to it, simultaneously bring about the coupling between the exciter and receiver coil system Wire frame is made.

It is one of the advantages of the inventive arrangement, that the, the displacement system partially forming wire frame at its two ends associated with the magnetic poles as a result to build up a magnetic field of the current flowing through it is able to perform the deflection, taking into account the inhomogeneous magnetic field prevailing there able to compensate and that the middle part of the frame, which is arranged perpendicular to it, simultaneously acts as a coupling element for the excitation and receiver coil is used, even the smallest

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Able to detect displacements of the displacement system are.

In order to increase the sensitivity of the measuring system still the wire frame is suspended in tensioning straps in a manner known from measuring instruments, which at the same time provides the compensation current respectively. The connection of the wire harness with the tensioning straps is made so that the supplied current is divided into equal parts at the connection point, and the flows through both wire frame halves in opposite directions. Through this Even external homogeneous magnetic fields remain without influence on the displacement system, since the effects of the compensation current cancel because of the opposing division both in the vertical and in the horizontal plane.

The structure and mode of operation of an exemplary embodiment are explained in more detail below with reference to the figures. It shows:

Pig. 1 schematically shows the structure of an exemplary embodiment two possible arrangements of the excitation coil system,

Pig. Figure 2 shows a block diagram of those belonging to the invention electrical switching elements,

Fig. 3 shows a possible practical embodiment for the depiction of the Hcheiiiazoi after Fip ;. 2

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Fig. 4 shows the transmission behavior of the inventive Arrangement.

The invention is primarily intended for measuring the Oxygen content of a gas. The measurable physical In the inventive arrangement, size is the force that on a largely non-magnetic body in an inhomogeneous magnetic field in the presence of an oxygen-containing gas is exercised. The following quantitative relationship exists for this force:

^F - ^K o2 * ^v ' ^H if

With H = magnetic field strength,

S = path in the direction of the gradient of the field strength, V = volume of the test or displacement body, Kp = susceptibility of oxygen or susceptibility of the gas mixture

The force exerted on the non-magnetic body is proportional to the susceptibility of the gas mixture and thus in practice proportional to the proportional mass of the oxygen in the gas mixture, since its susceptibility exceeds that of almost all other gases by an order of magnitude. In the embodiment of Figc 1 is the non-magnetic body on which a Kra ^ l. ^ untrained w:! ri _; represented by two glass spheres. -5 and 5 '»The glass spheres know hollow and evacuated

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or be filled with a gas of a certain composition. The glass balls 5 and 5 ^! are attached to a balance beam 6 or; form part of the same, the balance beam consisting of a wire frame, which continues at its two horizontal ends and rotated by 90 degrees perpendicular to its' longitudinal axis, the glass balls 5 and 5 ¹ equatorially with its parts 7 and 7 *.

The wire frame is preferably suspended by means of tensioning straps 8 and 8 'in such a way that the glass spheres are in the inhomogeneous magnetic field of two U-shaped permanent magnets, 1, 4 and 2, 3. The permanent magnets are provided with opposing pole pieces 4 'and 3' or I ¹ and 2 ¹ , which are shaped or beveled in such a way that an inhomogeneous magnetic field is formed between the pole pieces in such a way that they are closest to each other the pole shoes also have the greatest density of lines of force. The arrangement of the pole pieces is such that the glass balls are driven out of the area of high magnetic field density in the presence of a corresponding gas in the same direction of rotation, so that the torque on the vertically suspended frame 6 doubles overall.

The whole system is indicated by a dashed line

Surrounding housing 9, which is made gas-tight and is provided with its own gas inlet Io and a gas outlet Io.

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In the presence of an oxygen-containing gas, the

According to their high susceptibility, parts of the substance are drawn into the area of the highest density of magnetic lines of force and displace the glass balls from it, so that a torque is created on the tensioning straps.

The entire, made of electrically conductive material, for example-1 | wise copper wire, executed balance beam is designed as a short-circuit ring and encloses, as already mentioned, with two Loops twisted 90 degrees from its main surface also the glass balls.

In the exemplary embodiment encloses .the main surface of the wire frame 6 a fixed cylinder coil 12, which is attached in its center and serves as a transmitter or excitation coil, which also can be attached in a recess of the housing 9 and ^ is thus protected against the influence of corrosive gases. A high-frequency current flows in this cylinder coil, which is generated by an external oscillator 13 (see Fig. 2 or Fig. 3) • is generated. As a result, a high-frequency voltage is generated in the self-contained balance beam 6 designed as a wire frame induced, their size and phase from the position of the wire frame to the solenoid only to a very small extent Dimensions is dependent, especially since the wire frame also has only very small angles of rotation in the order of magnitude of about 1 degree executes. · ** "

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Instead of a fixed solenoid in the middle of the Wire frame 6 can also, for example, two separate Coils 14 can also be arranged in parallel below the wire frame 6, either within the housing 9 or also outside. The two coils 14, for example in series or fed in parallel by the same oscillator IJ are also shown in Fig. 1, although only one excitation coil, i.e. 12 or 14, is necessary to induce a high frequency voltage in the wire frame.

Elsewhere, for example above the wire frame within bzvi. also outside of the housing are a resp. further coils 15 arranged, the axis of which is perpendicular to the as excitation coils to be designated coils 12 and 14 and are thereby magnetically completely decoupled from these. . These coils are referred to below as receiver coils 15 are, however, arranged in such a way that a space is reduced in them via the wire frame 6 which is strictly linear

depends on the deflection of the balance beam, i.e. the size and phase of this induced high-frequency voltage are a measure for the angle of rotation of the balance beam system (see also

The receiver coil pair 15 is expediently vertical arranged to the plane of the short-circuit ring, so that the-

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ses is inductively coupled to the solenoid 12 or to the transmitter coils 14 exclusively via the short-circuit ring . ■■ .'_ ■

According to Pig. 2, the voltage induced in the receiver coils 15 is fed to an amplifier, preferably a high-gain RC amplifier 16 and then to a tk- phase rectifier system 17, at the output of which a direct current can be taken, the polarity of which is proportional to the direction of rotation and the amplitude of which is proportional to the angle of rotation This direct current, which is a measure of the volume fraction of oxygen in the gas mixture, is, • preferably via the strap bearings 8 and 8 ', fed back to the balance beam system β with the correct polarity in the sense that in the loops, ie in the the glass beads 5 and 5 comprehensive framework ends 7 and ^7! a force which acts the inhomogeneous magnetic field in the direction of the gradient, since the supplied current divides β to the point of attachment of the tension straps to the designed as a short-circuit ring wire frame, it also flows through each for. Half with the correct polarity, the two conductor loops, which are between the magnetic poles are located, so that a force couple arises on the spot which, with correct polarity, corresponds to the magnetic force generated there due to the displacement of the glass spheres, counteracts the deflection and this up to a slight,

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reverses the deflection required to maintain the current.

This system is a so-called torque compensation, which roughly corresponds to a rotary balance. The compensating couple of forces generates a torque that reduces the deflection to a very small remaining distance or remaining angle, which is necessary to generate the electricity used for compensation, reverses. The one to compensate The required current is a measure of the torque to be measured or the force that counteracts the displacement force and thus proportional to the volume fraction of the gas to be measured. A display instrument introduced into the current path of the compensation current can accordingly be calibrated in percent by volume of the respective gas.

Other measures can also be taken to excite the short-circuit ring, for example a galvanically impressed current or induction can be generated by a ring coil, through the center of which the wire frame passes, and, as already mentioned, the excitation can also be achieved by a second pair of frame-shaped Coils lh are generated, which are arranged parallel to the wire frame 12. In order to increase the coupling, iron or ferrite cores can also be provided in the coils.

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The receiver coils 15 can be connected in series or in parallel but are polarized in such a way that the signal induced in them amplifies when the moving system is rotated will; they are also through a parallel connected capacitance, as can also be seen from FIG.>, to the same resonance frequency matched to which the oscillator 13 oscillates. In one embodiment, it has a resonant frequency JP 'of about 47o kHz were found to be favorable. '

An exemplary embodiment of the only shown schematically in FIG The block diagram is shown in FIG. 3j, the dashed lines outlined 'parts correspond to the block diagram elements of FIG. The oscillator is made up of two transistors, whose Emitter connections are brought together, constructed and is galvanically completely separated from the other arrangements except for the line 18, which leads to the correct phase rectifier fc. leads. The transmission of the signal from the transmitter coil 12 or 14 to the receiver coil 15 takes place exclusively via the position of the only indicated schematically in FIGS. 3 and 2 Wire frame6, whose direction of deflection is exaggerated.

That fed into the receiver coil I5 in this way The signal is further amplified by a two-stage RC amplifier and then fed to a phase-correct rectifier. This can be done, for example, via another medium-long tap

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th transformer I9. Since the individual components for seen are known, is likely to be in this context no further entering into the matter; however, it is advisable to use the output signal of the rectifier with the correct phase to be further amplified via a downstream DC amplifier.

In any case, the compensation current flowing in the wire frame 6 holds - almost independent of the momentary oxygen concentration of the gas mixture to be measured - A certain orientation of the frame 6 with his two glass spheres 5 and 5 'upright.

However, care should be taken to ensure that the supply voltages are stabilized so that they are not caused by unintentional changes in the oscillator voltage or the gain factor Measurement inaccuracies occur.

Another particular advantage of the design of the wire frame 6 as a short-circuit ring can be seen in the fact that ^{the same current flows in both halves, for example based on loops 7 and 7 1} , so that through the Komperisatlonsstrom the moments acting on the glass spheres without any Reaction force on the strap mounting can be compensated on the spot. In addition, the arrangement according to the invention is completely insensitive and more homogeneous to the influence of outside

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- j. τ- - -.

Magnetic fields from any direction as the current in view an external magnetic field the two halves in opposite directions flows through, both in terms of the part with vertical orientation and the loops that are in a horizontal plane. This also compensates for the effect that an external magnetic field can exert. Lateral Movements of the displacement system, i.e. the wire frame 6 with the two glass spheres still have no influence on the zero point and the "sensitivity of the device.

It is also possible to use a separate oscillator instead of a separate oscillator and a subsequent amplifier to use a self-oscillating amplifier arrangement for the induced voltage in the sense that through the balance beam system in their coupling influenced receiver or transmitter coils 15 and 14 in the feedback loop of a corresponding Coupling ■ self-oscillating designed amplifier. The oscillation condition for this amplifier can be met exactly that it starts to vibrate with the slightest twist of the balance beam system. The oscillator voltage is rectified and, as already mentioned, returned to the wire frame with the correct sign in the compensation circuit. In this case, too, corresponds to The current required for compensation corresponds exactly to the volume fraction of the gas to be measured. The advantage of this arrangement is that

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apart from the simultaneous use of a single one The amplifier does not have any stabilization circuits, even as an oscillator must be provided for the oscillator or for a power supply unit.

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Claims (1)

1961532 / 1.! Device for magnetic gas analysis, especially for Determination of the oxygen content of a gas sample with an inhomogeneous magnetic field between the poles deflectable displacement system with non-magnetic end pieces and with a, the displacement system ^ giving a current proportional to the deflection traversed wire frame, which is generated by the electricity Magnetic field counteracts the deflection in automatic compensation, characterized in that "one, one Oscillator (I'j5) fed, fixed excitation coil system (1 ^, 12) and a receiver coil system '(15) are provided and that the 'coupling of the two systems takes place via the wire frame (6) assigned to the displacement system. 2. Device according to claim 1, characterized in that W the displacement system symmetrically about a vertical axis is constructed with two end pieces, each in one, • non-homogeneous formed from two U-shaped magnets Magnetic field are arranged. J). Device according to claim 1 and / or 2, characterized in that the non-magnetic end pieces (5 * 5 ^f ) located between the magnetic poles (1 ', 2'_;J> ^x , 4 ^T ). of the displacement system from the wire frame (7,7) in a horizontal 1098 17/0976 ./· original 1961532 Equatorial plane, i.e. perpendicular to the magnetic lines are and that the remainder of the displacement system from a perpendicular to it, the coupling between Causing exciter and receiver coil system (-12.15) Wire frame (6) consists. 4. Device according to claim 1, 2 and ~ $ » characterized in that the wire frame (6) is mounted in tensioning straps (8, 8 ') which at the same time supply the Kornpensat ionsstrom. 5. Device according to claim 4, characterized in that the Wire frame (6) the resilient element for the tension band suspension represents. 6. Device according to claim 1 and one or more of the preceding Claims, characterized in that the fixed The excitation coil system consists of a pair of coils (14), the winding planes of which are parallel to the rotatable frame (6) are arranged. 7 · Device according to claim 1 and one or more of the preceding claims, characterized in that the fixed Err.receiver coil system (15) from a coil pair consists, whose winding planes are arranged perpendicular to the rotatable frame (6) and an end face of the frame face. . 10981 7/0976 / ORIGINAL B, device according to one or more of the preceding claims, characterized in that the Viechseis voltage induced in the receiver coil system (17) is fed to an amplifier (16) with a subsequent phase rectifier (17), the output terminals of which are connected to the two tensioning strap bearings with the correct sign. ¹ 9. Device according to claim 1 to 5 *, characterized in that that as the excitation coil system a single, in the middle of the wire frame (6) arranged perpendicular to this and of this enclosed ring coil (12) is provided. 10. Device according to claim 9, characterized in that the excitation ring coil (12) is arranged in a cylindrical recess of a housing (9) which encloses the displacement system and the magnetic poles in a gas-tight manner and is accessible from the outside. 11. Device according to one or more of the preceding claims, characterized in that the receiver coil (s) (15) is (are) also arranged outside the gas-tight housing (9) perpendicular to the excitation coil (12). 12. Device according to one or more of the preceding Claims, characterized in that the gas flow . 109817/0976 / .! ÄfcHSiSQ. iJÄD OHlGiNAL '. - ■ 1961532 direction perpendicular to the axis of rotation of the displacement system lies. - Device according to claim 1, and one or more of the preceding claims, characterized in that as an oscillator, a switched in a self-oscillating arrangement amplifiers provided such that Receiver ¹ - (15) and transmitter coils (14) optionally Unreconciled in the form of resonant circuits in the feedback branch of a Resonant circuit amplifier are arranged, whose rectified oscillation signal is fed to the wire frame in compensation circuit with the correct sign. 109 817/0976 jÄMtsmo am® origin / «.