Apparatus for controlling or checking the irregularity of a flow of textile or like materials

Aug. 23, 1960 a. butticaz etal 2,950,436

APPARATUS FOR CONTROLLING OR CHECKING THE IRREGULARITY

OF A.FLOW OF TEXTILE OR LIKE MATERIALS

Filed April 15, 1957 4 Sheets-Sheet 1

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Filed April 15, 1957

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Aug. 23, 1960 a. butticaz etal 2,950,436

APPARATUS FOR CONTROLLING OR CHECKING THE IRREGULARITY

OF A FLOW OF TEXTILE OR LIKE MATERIALS

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Aug. 23, 1960 a. butticaz et al 2,950,436

APPARATUS FOR CONTROLLING OR CHECKING THE IRREGULARITY . , OF A FLOW OF TEXTILE OR LIKE MATERIALS

Filed April 15, 1957

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United States Patent Office

2,950,436

Patented Aug. 23, 1960

2,950,436

APPARATUS FOR CONTROLLING OR CHECKING THE IRREGULARITY OF A FLOW OF TEXTILE OR LIKE MATERIALS

Andre Butticaz, 45 Rue de la Bolle, Charles Tesage, 24 Rue Folmard, and Heinz Dembowski, 92 Rue de la Bolle, all of Saint-Die, France

Filed Apr. 15,1957, Ser. No. 652,785

Claims priority, application France May 3,1956 26 Claims. (Cl. 324—61)

The present invention relates to a method and apparatus for controlling or checking the irregularity of a flow of textile or like materials, with a view to measuring and/or recording the irregularities of strips, ribbons, wicks, threads, etc., made of textile material or other like materials.

The invention has also for its object to provide an indication and counting of the difference, either above or below, exceeding a pre-determined percentage with respect to a given mean value.

An indication of this kind offers in particular the possibility of determining the frequency of an irregularity observed in a flow of products resulting from a process of manufacture and to permit of the identification, for example, by means of measurement of the period or of the wave-length of the irregularity of the member or the stage of the manufacture which may be the cause.

The invention constitutes an application and a development of the method described in the U.S.A, patent specification filed October 1, 1956, under No. 613,099, for Process and Apparatus for Controlling a Flow of Textile Fibres or Similar Materials,” and consisting essentially in causing the flow of material to be controlled between the two plates of a condenser and in measuring the. increase in capacity of this condenser with respect to its value in the absence of the material: under certain conditions which are always obtained in practice, this variation in capacity is proportional to the mass of textile or like material introduced between the plates of the measuring condenser. Mention has been made in the above-mentioned patent of the advantageous use of a differential condenser forming a measuring condenser and a reference condenser on each side of a central plate, in association with means known per se as a whole, to translate the variations in capacity of the measuring condenser into a control signal. It is this same arrangement which has again been adopted in the scope of the present invention with a view to the formation of a regularimeter capable of checking the irregularity of a flow (thread, wick, strip, ribbon, etc.) of textile material or the like.

The method in accordance with the invention consists essentially in causing the flow of material to be controlled to pass at a constant but adjustable speed through a measuring condenser, in producing an electric out-ofbalance signal resulting from the comparison of the capacity of this measuring condenser with the capacity of a reference condenser, in comparing this out-of-balance signal with a signal which represents a mean reference value, and in controlling the variations of the differential signal resulting from this comparison and representing the irregularity.

In accordance with one method of procedure, a mean fixed pre-determined reference value is adopted corre2 sponding to the nominal characteristics of the flow of material under control, and in this case any irregularity will be termed an “absolute” irregularity.

In accordance with a further method of procedure, a 5 variable mean reference value is adopted corresponding to the mean real value of the signal obtained during a limited period of time preceding the instant of observation, and in this case the irregularity will be termed a “relative” irregularity.

Whether it is a question of absolute or relative irregularity, its instantaneous value may be observed and/or recorded in magnitude and in sign by means of appropriate instruments.

With a view to the determination of a mean value of 15 the irregularity, a full-wave rectification is effected of the differential signal obtained by a comparison of the actual value of the signal with the mean value of reference, this rectification being followed by an integration of limited memory of the differential signal thus rectified. 20 The result of this integration may be indicated in an intermittent manner at the end of each of a succession of discrete periods of integration, or again it may be indicated and/or recorded in a permanent manner.

These controls will preferably be completed by a de25 tection with a view to counting and indicating the crossing, by the actual value of the differential signal representing the irregularity, of two pre-determined threshold values Which are respectively positive and negative, the frequency of these crossings supplying information as to 30 the frequency of the irregularity. Before being subjected to this detection of departure outside a range of values, the signal will preferably be filtered in a low pass filter with an adjustable cut-off frequency, which enables the elimination at will of variations in frequency 35 greater than a certain value for a given speed of flow.

The apparatus proposed for the purpose of carrying the method described into effect comprises in accordance with a preferred form of embodiment, a measuring circuit formed by a high frequency oscillation generator 40 with a symmetrical output, a differential condenser comprising at least one measuring condenser and one reference condenser formed by two external plates arranged symmetrically on each side of a central plate, the outer plates being connected to the terminal of the said gen45 erator, a tuned amplifier, means for applying to the input of this amplifier the out-of-balance potential of the said central plate, a detector connected to the output of the amplifier, and an interpretation apparatus comprising a continuous reference source of potential and means for ₅₀ controlling variations of the differential signal resulting from the comparison of the potential delivered by the said detector with the reference potential.

For the purpose of varying its gain, the amplifier will preferably be provided on the one hand with a manual 55 regulating device and on the other hand with an automatic control device operating with a pre-determined time-constant, either the one or the other of these devices being put into use, depending on whether it is desired to observe the absolute or relative irregularity.

The interpretation device will preferably comprise a differential aperiodic amplifier with two input terminals which are respectively connected to tire reference source and to the detector; the differential signal delivered by this amplifier will be passed in the first place to an indicating and/or recording instrument by means of which variations in irregularity can be observed, and in the second place to a rectifier-integrator intended to determine the mean value of the irregularity, and thirdly to a device for detecting, indicating and counting the passages of the irregularity beyond two threshold values, respectively positive and negative, and which are separately adjustable.

2,950,436

The special features and advantages of the invention will become further apparent from the description which follows below of a form of embodiment given by way of example, reference being made to· the accompanying drawings in which:

Fig. 1 is a general diagram of the apparatus.

Fig. 2 is an explanatory diagram of the operations of measurement of irregularity.

Fig. 3 is a diagram relating to the operation of selection and counting of amplitude.

Fig. 4 is a perspective view of the measuring condenser.

Figs. 5, 6 and 7 are front views of the three first plates of this condenser.

Fig. 8 is a view in cross-section taken along the line VIII—VIII of Fig. 7.

Fig. 9 is a diagram showing the measuring circuit and the gain-control device of the amplifier.

Fig. 10 is a detail view in cross-section of a part of the amplifier casing.

Fig. 11 is a diagram showing the shape of the frequency-response curve of the automatic gain-control device.

Fig. 12 and Fig. 12α taken together are an electrical diagram of the interpretation apparatus unit.

In accordance with the form of embodiment shown diagrammatically in Fig. 1, and intended to control the irregularity of a strip, ribbon, wick or thread 10, the latter is caused to pass at a constant speed, by means of a pair of driving rollers 11, coupled to a motor (not shown), between the central plate 12 and one of the outer plates 13, 14 of an air condenser of the symmetrical or differential type. Each of the armatures 12, 13 and 14 is framed in known manner by corresponding keeper of antistray plates 12', 13' and 14' held at the potential of the mounting frame and intended to make the electric field uniform between the plates by eliminating the edge effects. The outer plates 13, 14 are connected by symmetrical wires 15, 16 to the two terminals of a balanced output transformer 17 of an oscillator 18, the centre point 19 of the secondary winding of this transformer being connected to the earth of the assembly.

The central plate 12 is coupled through a coupling condenser 20 and a leakage resistance 21 to the input grid of a tuned amplifier 22. The output signal from this amplifier is simultaneously applied to the input of two detectors 23 and 24. The detector 23 supplies an automatic gain-control 25 for the tuned amplifier 22. This gain may also be controlled by a manual regulation shown by the arrow 26. The detector 24 supplies an interpretation device, of which the unit is indicated by the reference 27.

The interpretation device comprises a differential amplifier 28, to the input of which is applied on the one hand the detected voltage from 24, and on the other hand a continuous reference potential or datum potential supplied by a source of reference 29. The differential signal resulting from this comparison is applied in the first place to an indicator instrument 30 with a central zero, enabling an instantaneous positive or negative value to be read at any moment.

The signal is applied in the second place to a rectifierintegrator 31, to the output of which is connected an indicating instrument 32 with left-hand zero, enabling the mean integrated value to be read with a certain timeconstant of the said differential signal. The latter is finally applied in the third place to a device 33 known as an amplitude counter and comprising two indicator lamps 34, 35 of different colours (red and green for example) and arranged so as to light the first lamp when the signal passes over a pre-determined and adjustable positive threshold value, and to light-up- the second lamp when the signal passes over a negative threshold value which is also predetermined and adjustable.

-Before beginning the detailed description of an example of construction of these various elements of the apparatus in accordance with the invention, and in particular of the interpretation device, with reference to Figs. 4 to 12, the method of measurement or control of the regularity will first of all be explained with reference to Figs. 2 and 3.

If a great length of thread, wick or ribbon is weighed per unit of length, centimetre by centimetre, for example, there is obtained a curve the general shape of which is that shown by the curve in full lines given in Fig. 2, in which P is the weight per unit of length, plotted as ordinates, and L is the length plotted as abscissae. By integrating a curve of this kind, or by dividing the total weight by the total length, a mean weight Pm can be determined; the straight line MM' parallel to the axis of the abscissae, at an ordinate value Pm, would be the curve of a perfectly uniform thread of the same “metric number.” The “metric number” Nm is the term given to the quotient of the length in metres by the weight in grams; it is thus the reciprocal of the mean weight as defined above. By “irregularity” is meant the deviation of the real curve from the ideal straight line MM': it is thus essentially a variable quantity, changing in sign at a certain frequency, depending on the conditions of manufacture of or treatment of the thread, wick, ribbon, etc

In accordance with the invention, it is proposed on the one hand to measure the mean value of the irregularity, and on the other hand to obtain information as to the frequency of its variations.

The out-of-balance signal applied to the input of the amplifier 22 being proportional to the mass of . textile or like material which is located at any instant between the plates of a measuring channel, the same thing will be true of the amplitude of the signal applied to the input of the detectors 23 and 24 with the reservation that the potential delivered does not pass out of the range of linearity of the amplifier. The rectified voltage will, under these conditions, be subjected to variations in function of time corresponding to the curve in full lines as shown in Fig. 2, the time scale being obviously coupled to the scale of lengths L by the speed of passage adopted. By varying the gain of the amplifier in such manner that for a thread, strip or ribbon of mean weight Pm, the rectified voltage will be equal to the reference potential of the source 29 (see Fig. 1), it is seen that the instrument 30 will indicate at every instant the instantaneous value of the irregularity as defined above, and this instrument may with advantage be graduated directly in percentages, on each side of the central zero.

The control of the gain of the amplifier may be effected either by hand or automatically. In the case of manual regulation, the gain is controlled in a fixed manner, using a previous calibration as a base, to a value such that the detected potential applied to the input of the differential amplifier 28 is equal to the reference potential of the source 29 for a predetermined nominal weight or metric number. The measurements of the irregularity will then be carried out with respect to this predetermined nominal or theoretical weight, and it is this that will be termed an “absolute” measure of the irregularity.

In the case of automatic control of the gain by means of the circuit 25, the gain will be automatically controlled in such manner that the real mean level of the detected potential remains constantly adjusted to the reference potential, the said mean level being established with a certain time-constant proper to the circuit 25, that is to say on the basis of an integration of the output potential with a limited memory. The measurements of the irregularity will then be effected with respect to this real mean weight measured over a certain length of thread, ribbon or strip, and it is this measurement which

2,950.436

Will be termed a “relative” measurement of the irregularity.

In the rectifier-integrator 31, the signal passing out of the differential amplifier 28 is first subjected to a fullwave rectification which supplies a quantity corresponding in Fig. 2 to the curve forming the upper contour of the shaded surface, this curve being obtained by reversing in symmetry with respect to the straight line MM', all the negative half-waves of the irregularity curve. By integration of this rectified signal, there is then obtained a mean level Em, and the ratio Em/Pm will represent the desired mean value of the irregularity, which will be preferably indicated directly as a percentage On the instrument 32 which is graduated from zero to 100%. This value will be an absolute mean value in the case of a manual control of the gain, fixing the straight reference line MM' at a level corresponding to a pre-determined theoretical nominal weight or metric number; it will be a relative mean value in the case of automatic gain control, in which case the straight reference line MM' will in fact be replaced by a slowly-varying curve having ordinates which correspond at every instant to the real mean weight of a certain length of thread which has previously passed through the measuring condenser.

Finally, in order to obtain information on the periodicity of the irregularity, there is arbitrarily fixed a positive threshold E_x (see Fig. 3) and a negative threshold value E₂ with respect to the mean value MM' and the periods of overrunning p₁₍ p₂, p₃ . . . _ni, n₂, n₃ . . . of these two respective threshold values will be observed. This operation is effected in the device 33 known as an amplitude counter, the positive over-runs p and the negative over-runs n being indicated respectively by the lighting of the two lamps 34, 35. This device will preferably comprise a low-pass filter with an adjustable cutoff frequency which enables the variations, the frequency of which exceeds the cut-off frequency to be eliminated for a given speed of passage and in consequence to smooth-down” the curve examined to a corresponding extent.

Figs. 4 to 8 show a preferred form of embodiment of the measuring condenser. With a view to a better adaptation of the threads, wicks and ribbons, the condenser is provided with four measuring channels, of which two are for the threads. To this end, it is provided with nine plates 41 to 49, each separately fixed by means of screws on a base 50. Both plates and base are of electrolytic copper; the surfaces are polished and chromiumplated in order to prevent wear and corrosion, and to reflect thermal and light radiations.

As can be seen in Fig. 5 for example, with respect to the first plate 41, an internal zone such as 41α of small surface has been cut-out of each plate, this zone being insulated from the external zone 416 by a layer 41c of insulating low-loss material such as mica or trolitul for example. In each plate, the inner zone a forms a plate of the condenser, whilst the outer zone forms the corresponding keeper plate. The plate 42 thus forms the central plate and the plates 41 and 43 are the two outer plates of a first differential condenser or first measuring channel. The plate 44 of smaller height than the preceding plates forms the central plate of a second differential condenser or measuring channel; it is enclosed between the plates 43 and 45. The central zone 43α of the plate 43 thus forms an outer plate at the same time for the first and for the second measuring condenser; as shown in Figs. 7 and 8, it is cut-out with a bevelled edge, so that its face turned towards the plate 42α is higher than that turned towards the plate 44α, which is smaller than 42α. The same condition applies for the inside zone of the plate 45 which is associated at the same time with condensers No. 2 and No. 3, and for the inner zone of the plate 47 which forms part simultaneously of the condensers No. 3 and No. 4.

⁶

Figure 9 shows the diagram of the measuring and gain-control circuits.

Three parallel wires 51, 52, 53 are stretched to form a flat surface in a hollowed-out portion formed for that 5 purpose in the base of the measuring condenser (see also Fig. 10): the central plates 42α, 44α, 46α and 48α are connected to the central wire 51, whilst the outer plates are respectively connected to the outer wires 52 and 53. Two screws 54 and 55 can be passed at will 10 either between the wires 51, 52 or between the wires 51 and 53; the first is used for the “zero setting” or the balancing of the measuring condenser, whilst the other, when it is fully screwed home serves to produce a welldefined change in capacity for the purpose of calibration 15 of the apparatus. This “calibrating screw” is normally unscrewed.

The oscillator comprising a tube 60 is of a standard type with a grid coil 61, a plate coil 62 tuned by a condenser 63 and a balanced coupling coil 64 having a cen20 tre point earthed. The working frequency is for example 100 kilocycles per second. The oscillator assembly is placed in a compartment 65 of a screened casing 66, of which a further compartment 67 contains the. input stage of the amplifier. The base 68 of the measuring 25 condenser carries two threaded rods 69, 70 which pass respectively into the compartments 65 and 67 inside insulating guide tubes 71 and 72 respectively. The rod 69 carries a magnetic core 73 on which is formed the coupling coil 64. The tube 71 carries the grid coil 61 and 30 plate coil 62 arranged round the coupling coil 64. The coupling coil 64 comprises a bi-filar winding, and it is connected by plaited connection wires 73 to the outer wires 52 and 53 of the measuring condenser.

The central wire 51 of the measuring condenser is ³⁵ connected by a wire 74 to the coupling condenser 20, already referred to in connection with Fig. 1. This condenser is formed by a cylindrical condenser comprising an inner plate 75 carried on the threaded rod 70 by means of an insulating core 76, and an outer plate 77 carried 40 on the insulating tube 72.

The base of the measuring condenser thus forms a single unit with its coupling members to the oscillator on the one hand and the amplifier on the other. The arrangement described ensures however a strict separa45 tion of the oscillator from the amplifier, avoiding all direct induction, both electro-magnetic and electro-static; it also avoids any very delicate direct contacts in the coupling zone, since an even very small change in contact resistance would result in phasing errors and in con50 sequence in errors of measurement.

The construction of the amplifier 22 itself does not give rise to any special difficulty and will not be described in a detailed manner; although a relatively high gain is desirable, it is possible to avoid the necessity for fre55 quency changing and to employ only a direct amplification. It will be necessary to take precautions in respect of the construction of the first stage, which should be decoupled in a particularly efficient manner on the one hand with respect to high frequency, and on the other ⁶⁰ hand to suppress all the residual hum of the high tension, which will be stabilised. At the output, a push-pull stage will preferably be provided in order to feed the two detectors 23 and 24 by means of a transformer 80 hav_6g ing two identically similar secondaries.

The cathode of the first amplifier tube 81 may be connected either to a fixed resistance 82 or to a group of three potentiometers 83, 84 and 85. This change-over is effected by means of a change-over switch I with four 70 blades and three positions a, b and c. The position a corresponds to the manual gain-control, the position c to automatic control, whilst the position b is an intermediate transition position. A resistance 86 arranged in parallel with the tube 81 and its load 87, formed in the 75 usual manner by a circuit tuned to the frequency to be

2,950,436 '7 8 amplified, forms with the cathode resistance 82 or 83 to 85 a potential divider which tends to compensate for the effect on the gain of the first stage, of any possible variations of the anode potential, by a corresponding variation of the potential of the cathode. 5

It will be noted that in the manual gain control position (position a of the switch I), the control grid of the tube 81 is connected through the leakage resistance 21, the wire 88 and the wire 89 to the slider of the potentiometer 85. In the automatic control position (posi- 10 tion c), it is connected by the wire 88 to the output of the filter with two resistance-capacity sections 91—92 and 93—94, the input of which is then connected by the wire 95 to the negative terminal of the detector 23, whilst the positive terminal of this detector is connected by a wire 15 96 to the slider of a potentiometer 97 inserted in a series potentiometer group 98 connected between the high tension supply and earth. The wire 88 is connected on the other hand through a diode 99 to a point 90 of this group, which fixes a maximum limit (+4 volts for ex- 20 ample) to the direct current potential of the grid.

The slider of the potentiometer 97 being fixed on the other hand at a higher potential which is known as the positive reference potential (of -|-65 volts for example), it can be seen that the potential applied to the input of 25 the filter is the result of the comparison of the detected potential -with this reference potential.

In the position b of the switch I, the resistances 91 and 93 are short-circuited and the -filter is reduced to two condensers 92 -and 94 in parallel: the change-over to this 30 position enables the condensers 92 and 94 to be instantaneously charged and thus avoids useless waiting periods. In the position c, the filter is inserted between the input wire 95 and the output wire 88. A damping resistance 100 arranged in series with the first condenser 92 35 serves to attenuate the resonance by positive reaction which tends to be produced at a certain value of frequency, by reason of the double de-phasing effect.

Fig. 11 shows the shape of the response curve obtained under these conditions: the magnitudes plotted in 40 abscissae are the frequencies of the variations of the amplitude of the input signal, that is to say variations in the capacity of the measuring condenser resulting from variations in the thickness of a thread, for ex-ample, whilst as ordinates there have been plotted the relative values at ⁴³which these same variations are found at the output side of the amplifier. It can be seen that the effect of very slow variations (low frequencies) is completely suppressed by the regulation; that there is then an intermediate zone in the vicinity of the opening frequency fo 50 of the filter, a resonance zone r of slightly higher value, and a progressive transition to the “normal” zone at which the variations of the output signal faithfully reproduce those of the input signal. By introducing the notion of wave-length of the variations in irregularity 55 of the thread or ribbon under study, that is to- say the ratio of the speed of passage to the frequency of the variations, it can be said that the automatic regulation causes the suppression of the effect in the output signal of the variations of long-waves lengths, that is to say of θθ wave-lengths definitely greater than a wave-length of cutoff; it is clear that this wave-length of cut-off is proportional, for -a given thread, to the speed of passage and that, in consequence, by increasing this speed, it is possible to progressively cause to appear in the output sig- ⁶⁵nal variations which are slower and slower and the effect of which was previously suppressed.

These considerations show a further aspect of the difference between the absolute measurement and the relative measurement of the irregularity: with the absolute 70 measurement (manual gain regulation) all the variations appear both slow and rapid; the relative measurement (automatic gain regulation) suppresses the variations having frequencies lower that the opening frequency fo of the filter forming the regulation circuit, or in other ⁷ words, the variations in wave-length greater than the wave length corresponding to cut-off. This wave-length being however proportional to the speed of passage, an increase in this speed will have -the effect of bringing closer together the relative measurement and the absolute measurement.

The description can now be given of one form of embodiment of the interpretation device itself, with reference to the diagram shown in Fig. 12. The rectified potential delivered by the detector 24, represented by U is compared with a positive reference potention Uo, taken from a potentiometer group 181 provided for that purpose between the positive of the stabilised high tension supply and earth. A series of calibrated resistances 102 to 105, connected between the output of the detector and the tapping 106 on the potentiometer group, enables he whole or a fixed fraction of the differential potential U—Uo to be taken-off by means of a rotary switch 107, and thus to obtain various sensitivities of measurement. Thus, for example, in the first position marked “12.5%,” the whole of the said potential is taken-off through the intermediary of a series protecting resistance 108; in the position “25%,” one-half; in the position “50%,” one- / quarter, and in the position “100%,” one eighth of the said potential. The two last positions “R” and “B” are used in the calibration operations of the apparatus. _f

The signal taken-off by the switch 107 is transmitted by the intermediary of a low-pass resistance-capacity filter 1®9—110, which can be put partly or wholly out of action by means of a double change-over switch II with three positions: in the position a, the filter is out of action (condenser open circuited, resistance short-circuited); in the position b, the resistance remains short-circuited, but the condenser is in circuit and in practice absorbs the very rapid variation; in the position c the entire filter is inserted and produces a damping of the frequencies greater than its cut-off frequency; this facilitates a search for the “mean” on long wave-lengths.

The signal taken from the output of this filter passes through one of the four contacts of a four-pole switch with two positions (a, b) or reversing switch III in order to be brought by a wire 111 to the control grid of a differential amplifier 28 with two tubes 113, 114 connected as a cathode-follower circuit; the signal is collected at low impedance between the cathodes at 115 and 116, at the head of two load resistances 117, 118 of equal values. The grid of the second tube or reference tube 114 is connected to the slider of a potentiometer 119, connected in parallel to the bridge 101 on each side of the reference potential tapping 106.

In position a of the reversing switch III, the indicator 30with a centre zero is connected between the points 115 and 116, and in the position b of the said reversing switch; the indicator 32 with left-hand zero or integration indicator is connected between the same points 115 and 116. Suitable variable resistance 121, 122 are respectively connected in series with these two instruments. In addition, there is permanently connected between the output terminals 115 and 116 of the amplifier a branch containing a variable resistance 123 and a jack 124 intended to permit of the connection of a recorder by means of a plug. The resistance 123 is short-circuited when the plug is engaged in the jack and replaces the recorder when the latter is disconnected, so as to avoid a modification of the total impedance coupled between the terminals 115 and 116.

The signal available between the terminals 115 and 116 of the differential amplifier is on the other hand simultaneously applied to the input of the rectifier-integrator 31 and to a device known as the amplitude-counter, the whole of which is indicated by the reference 33.

The rectifier-integrator 31 comprises essentially a bridge of diodes 132 intended to charge an integrating condenser 134 (of 2 microfarads for example) by the full-wave rectified signal potential, through the intermediary of a load

2.980.486 resistance 133 of very high value (20 megohms for example). The load resistance is shunted by a push-button 135 which enables the condenser 134 to be charged or discharged instantaneously during a checking of the calibration. In parallel with the integration circuit 133—134 is connected an auxiliary source of voltage 136, of 20 volts for example, in series with a resistance 137 of 2 megohms for example. This auxiliary circuit is provided in order to make the discharge resistance practically equal to the charge resistance, this being an essential condition in order to obtain a correct integration, that is to say a good linearity and a very low threshold of excitation. The integration is effected with a memory limited to periods of the order of the time-constant, or forty seconds with the values given by way of example. For long lengths of thread, a number of successive integrations will thus be carried out, separated by periods of about thirty seconds for example.

After each integration period, the reversing switch III is turned over to the position b, which has· the effect of changing-over the positive plate of the integrating condenser 134 to the slider of a potentiometer 120 connected in parallel with the potentiometer 119, and its negative plate to the grid of the tube 113: the instrument 32 is substituted at the same time for the instrument 30, and its deflection indicates the mean level of the irregularity during the period of integration considered.

The amplitude-counting device 33 comprises at its input a variable loss-pass filter 140—141 which has a cut-off frequency variable between certain limits, so that the variations of frequency greater than this cut-off frequency will be eliminated from the signal passed to the counter. The signal having passed through this filter is applied through the medium of a protection resistance 142 to the slider of a potentiometer 143 forming part of a potentiometer chain connected across the terminals of an auxiliary polarising source 144, of about 20 volts for example. Two other potentiometers 145 and 146, forming a second chain at the terminals of the source 144 have their sliders connected to the grids of two thyratrons 147 and 148 through the intermediary of the respective coupling resistances 149 and 150. Condensers 151 and 152 are connected on the other hand between the grid and the cathode of each of the thyratrons. The latter are supplied between cathode and anode by a source 153 of alternating-current potential and are loaded respectively by the relay windings 155 and 156, shunted in the usual manner by a condenser-resistance combination 157, 158.

The contacts of the relays 155 and 156 control, one at rest and the other in the working position, the lighting of the respective lamps 34 and 35, one of which is intended to indicate the passage above and the other the passage below two given threshold values. These two lamps are supplied from an alternating source 159 of 6.3 volts for example. The relays operate in addition the respective counters 161 and 162.

Finally, a switch 160 is arranged between the input of the device and earth: when this switch is closed, a highly negative potential is applied to the grids of the thyratrons (the cathodes of which are brought up to the potential of the output 116, or -)-60 volts for example), so that the counting is then stopped.

As the thyratrons become active at a certain negative value of the biasing potential of their respective grids, thjere results an asymmetry between the behaviour of the two thyratrons, which is compensated for by means of the potentiometer 143; in other words, this potentiometer serves to ensure the symmetry of behaviour of the two thyratrons with respect to a zero input voltage corresponding to the reference line MM' of Fig. 3. The potentiometers 145, 146 serve on the other hand to fix respectively the passage of the lower threshold E2, below which the relay 155 operates to light the lamp 35, and the passage of the upper threshold El, above which the relay 156 operates to light the lamp 34.

It is known that the operation of thyratrons supplied on the anode with alternating current and controlled at the grid by a continuous or slowly varying potential, is unstable in a circuit of the kind employed here: the 5 firing curve is actually displaced, depending on the value of the direct current potential at the terminals of the condenser which shunts the anode load, and this results in hunting. This drawback is avoided in this case by means of the resistance-capacity sections 149—151 and 150— 10 152, which play the part of stabilisers. By a suitable choice of the time constant of these sections, an excellent regularity of operation is obtained, the difference between the firing and extinction thresholds being reduced to about 0.5 volt for example, for an anode poten15 rial of 120 volts R.M.S. The time-constant of the stabilising sections will be of the order of magnitude of the period of the alternating potential of the anode supply. The results indicated above were obtained, for example, with a supply at 50 cycles per sec. with resist20 ances 149, 150 of 10 megohms and condensers 151, 152 of 2,000 micromicrofarads.

The form of embodiment which has just been described is simple and economical in construction and has the additional advantage of being very easy to use. 25 In particular, it lends itself to a calibration and re-calibration which is both rational and simple, so that the operator himself can regularly carry out a check of the calibration and even a complete re-calibration which may be made necessary from time to time by the inevi30 table wear of the electronic tubes. In this way, returning the apparatus to the works and visits of technicians are avoided, both of which are costly and useless, since the complete calibration can be carried out in a time of the order of one minute.

Calibration comprises the following operations:

After checking and when necessary correcting, in the usual manner the.zero settings of the indicating instruments and also the supply voltages, the rotary switch 107 (Fig. 12) is first of all placed in the position B, and 40 the change-over switches I, II and III in the position a. The reference potential is then applied to the input of the differential amplifier 28. By acting on the potentiometer 119, the needle of the indicator 30 is brought back to zero. The push-button 135 is then depressed ₄₅ for half a second, to short-circuit the load resistance 133 of the integrating condenser and ensure the discharge of the latter, the reversing switch III is then changedover to the position b; as the instrument 32 should then indicate zero, its deflection is adjusted by acting on the ₅₀ potentiometer 120.

The rotary change-over switch 107 is then put into the position R (equivalent to the position “100%”); in the absence of a signal, the centre-zero instrument 30 should then indicate —100%. This deflection is adjusted 65 by acting on the series resistance 122. By depressing the short-circuited button 135, the instantaneous charge of the integrating condenser 134 is ensured at the maximum potential corresponding to 100% irregularity: after having turned the reversing switch III into the position _eo b, the series resistance 121 is adjusted, if this is necessary, so as to bring the instrument 32 to the corresponding deflection, after which the reversing switch III is brought back to the position a.

The manual gain control potentiometer 84 (see Fig. 9) gg is provided with a regulating dial graduated in usual values of metric number or of nominal weight of thread, strip, ribbon, etc., depending on the applications considered. This is placed on a reference mark corresponding to the minimum nominal weight or maximum metric 70 number provided for. The zero-setting screw or balancing screw 54 of the measuring condenser is then regulated so as to bring the needle of the irrggurality indicator 30 to the position —100%: this amounts to the same thing as adjusting the balance of the measuring condenser in 78 the absence of material under test. The calibrating

2,950,436 ii screw SS is then introduced fully into the screwed hole provided for that purpose; the change in capacity produced by this calibrating screw replaces the change in capacity which would be caused by a standard of textile or like material, since it is not possible to establish a durable standard of such material. The other potentiometer 83 of the manual gain control device is then adjusted so as to bring the needle of the indicator 30 into the position +100 %.

Still keeping the calibrating screw fully engaged, the dial potentiometer 84 is brought into another position marked for that purpose, and for which the third potentiometer 85 of the manual gain-control device is adjusted so as to bring the needle of the instrument 30 on -to a corresponding mark situated at —80% for example. The calibrating screw is then disengaged.

It only remains to adjust the reference potential employed in the automatic gain-control circuit, in opposition to the potential detected by the detector 23, that is to say the position of the slider of the potentiometer 97 (see Fig. 9). For this purpose, there is introduced for example a thread of average metric number into the measuring condenser, and the rotary change-over switch (Fig. 12) is put into the position of maximum sensitivity (“12.5%” for example); the potentiometer 97 is then adjusted so as to bring the needle of the indicator 30 opposite its central zero. It is thus made sure that the automatic gain-control device really tends to regulate the potential delivered by the detector 24 to a value equal to the reference potential Uo which is employed at the input of the interpretation device.

The calibration is then finished and the apparatus is ready for use. It can be seen that the various adjustments are entirely independent one from the other, that is to say they have no mutual influence on each other. This particularly useful property enables, in addition, an arrangement to be employed such that the various regulating and adjusting members on the control panel of the apparatus are each disposed either opposite the reference mark as a function of which it is to serve, or is characterised by a colour matching with that of this mark; these two methods may of course also be combined. Thus, for example, the spindles of the potentiometers 83 and 85 which will be operated by a screwdriver will be placed opposite the two respective reference marks of the scale of the potentiometer 84, on to which this latter has to be brought during the corresponding adjustments; the spindles of the potentiometer 119 and of the rheostat 112 will be placed respectively opposite the positions B and R of the rotary change-over switch 107 opposite which the knob of this switch should be placed during the corresponding adjustment, etc.

It will be appreciated that this arrangement still further facilitates the operation of calibration and enables all risk of error or confusion to be avoided.

The invention is of course not limited to the forms of enbodiment chosen and shown, these having been given by way of example only; the invention may, on the contrary be given various alternative forms which will be clearly apparent to those skilled in the art, both as concerns the construction of the condenser and the measuring circuit and also that of the interpretation device itself.