4591 4595.output

* GB784998 (A)

Description: GB784998 (A) ? 1957-10-23

Improvements in or relating to tool bit supporting devices for machine tools

Description of GB784998 (A)

PATENT SPECIFICATION Inventor: JOSEPH LUKE Date of filing Complete Specificat Application Date: Nov IS, 1954. Complete Specification Published: BLACKLOCK ion: Aug 22, 1955. No. Oct 23, 1957. 784,998 33054/54. Index at acceptance:-Class 83 ( 3), W( 6: 7 A 1). International Classification:-B 23 d. COMPLETE SPECIFICATION Improvements in or relating to Tool Bit Supporting Devices for Machine Tools We, DRUMMOND BROTHERS LIMITED, a British Company, of Ryde's Hill, Guildford, Surrey, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: - This invention relates to a tool bit supporting device for machine tools. A tool holder is known which comprises a tool bar having a transversely arranged conical through-opening near one end, a cross-bolt for said bar formed with a head part and having the portion next to the head' part made to a size and taper corresponding to the conical part of the opening in the bar, said head and' conical part being slit and bored to receive the tool, the arrangement being such that, upon the bolt being tightened' up in relation to the bar, the split portions of the bolt grip the tool and at the same time the bolt becomes securely held to the bar With this known tool holder, the end thrust taken up by the tool will depend upon the degree to which the

bolt is tightened up, and, also, the tool is mounted nearly horizontally, so that there may be considerable bending strain on the tool when it is cutting. According to the invention there is provided a tool bit supporting device for machine tools, wherein a tool block is formed at one end with a recess for the reception of a tool holder, the recess being of diminishing crosssection towards the bottom thereof and having a bore extending from said bottom to accommodate a shank of said tool holder, said tool holder having at least one hole for the reception of a tool bit, whilst the shank extends away from the holder in a direction lateral to the axis of the, or each hole, said holder having a split extending from the,,or each hole to a part of said holder to be positioned near to the bottom of said recess, and, wherein stop means is associated with the tool block for engaging the, or each tool bit beneath the lPrice 3 s 6 d l end thereof remote from the cutting end, the arrangement being such that when a tool bit is placed in the, or each hole and the shank is drawn into the block, the holder is drawn into said recess thereby forcing the split portions of the holder towards each other and causing the, or each tool bit to' be tightly gripped in the, or each hole, and such that, in the operation of the device, end thrust 'on the or each tool bit is taken up by said stop means. For a better understanding of the invention, and to show how the same may be carried into effect, reference will now be made to the drawings accompanying the Provisional Specification, in which: Figure 1 is a side elevation of a complete tool bit supporting device, Figure 2 is an end view corresponding to Figure 1, Figure 3 is a view similar to Figure 2 but showing the other end, Figure 4 is a part plan view corresponding to Figure 1, and Figures 5, 6 and 7 are views all similar to Figure 4 but showing modified constructional forms. Referring first to Figures 1 to 4, there is shown a tool block 1 having a longitudinal bore 2 which opens, at one end upon the bottom surface 3 of a recess The latter is of diminishing cross-section towards the bottom surface 31, having two relatively inclined opposing side surfaces 4 and 5 At one end of the block 1, the bore 2 is enlarged in diameter as at '6 to accommodate a tubular nut 7 having an accessible head 8 The tubular nut 7 has internal screw-threading as at 9 for engagement with external screw-threading formed upon one end, of a shank 10 The shank 10 is integral with a tool holder 11, which has inclined faces for engagement with the inclined opposing side surfaces 4 and 5 of the block 1 There 'is a hole formed, in the tool holder for accommodation of a tool bit 12. The axis of the hole accommodating the tool bit is substantially vertical but is slightly indclined to the vertical both laterally and

forwardly of the tool block so as to allow to the tool bit the necessary side and front clearances. It will be noted that the axis of the hole accommodating the tool bit 12 is such that the shank 10 extends away from the holder in a direction lateral to such axis The holder 11 is split as at 13, between the hole accommodating the tool bit 12 and a location near to the bottom surface 3 of the recess in the tool block The split in the illustrated example extends into the shank itself as appears from Figure 4. The block 1 is fcrmzd with an integral teepiece 14 which extends beneath the lower end of the tool holder 11 The toe-piece 14 has an internally screw-threaded bore for the reception of an adjustable stop 15, the head' of the latter engaging the bottom 'of the tool bit 12 Through the intermediary of the adjustable stop screw 15, the toe-piece 14 takes up any downward thrust on the tool bit. In the employment of the tool supporting device described above, the nut 8 is slackened so that the shank 10 rides forward and tends to carry the tool holder 11 out of the recess in the wol block The tool bit 12 can now be freely inserted in the hole therefor in the tool holder The nut head 8 is now tightened thereby drawing the shank 10 into the block and consequently drawing the tool holder into the recess in the block The inclined opposing side surfaces 4 and 5 of the tool block engage the split portions of the tool holder and tend to close the split 13 therein In this way the tool holder tightly grips the tool bit 12 The adjusting screw 15 is brought to an appropriate position for the support of the base of the tool bit, and thereafter the tool supporting device is ready for use. Figures 'S and,6 'show the case,where a tool bit of non-circular cross-section is used InFigure 5 a tool bit 12 A of substantially triangular cross-section is shown The hole for the accommodation of the bit 12 A in the holder 11 is of correspondingly triangular cross-section In Figure 6 a tool bit 12 B of rectangular cross-section is shown and again the holder 11 has a hole, of corresponding cross-section, to accommodate the bit. In Figure 7 a modified form of holder 11 is shown formed with two holes for the accommodation of two circular cross-section tool bits 12 C There are two splits 13 A in the tool holder 11 but the arrangement is otherwise substantially identical to that described with reference to Figures 1 to 4. It will be appreciated that since the tool is effectively held in position by one nut located at the rear end of the tool block, where a number of tool blocks are bunched together, as a on a multi-tool lathe, any one tool bit can be readily removed without interfering with any other tool block.

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* GB784999 (A)

Description: GB784999 (A) ? 1957-10-23

Waveform handling devices for binary coded pulse signalling systems


PATENT SPECIFICATION 784999 4 ' Date of Application and filing Complete Specification Nov22, 1954. & No 33827/54. ((ii( O Application made in France on Nov20, 1953. Complete Specification Published Oct 23, 1957. Index at Acceptance:-Classes 40 ( 1), H 11 B 15; and 40 ( 5), L 26 (C 3: C 5: D: G 2 A). International Classification: -GO 8 c H 03 d H 04 c. COMPLETE SPECIFICATION Waveform Handling Devices for Binary Coded Pulse Signalling Systems We, SOCIETE D'ELECTRONIQUE ET D'AUTOMATISME, of 138, Boulevard de Verdun, Courbevoie, Seine, France, a Company incorporated according to the laws of France, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: - The present invention relates to devices for handling the waveform of binary pulse code modulation signals. In a conventional representation of such signals, each pulse period thereof is allocated a numerical significance viz a binary digit 1 or a binary digit 0 according to whether or not a pulse is present in the

said pulse period. There also exists another representation of signals of such a general kind wherein each 1 type binary signal is in a first form for the first half of its digit period and in a second form for the second half of its digit period while each 0 type binary signal is in the second form for the first half of its digit period and in the first form for the second half of its digit period. According to the present invention, we provide a device for handling a conventional binary signal waveform and converting it into a binary signal of the said other waveform comprises at least one bistable trigger stage having two symmetrical and separate actuation inputs and at least one output lead, means for electrically differentiating the incoming waveform and applying the pulses thus obtained to one of the actuation inputs of the trigger stage, means for deriving from the incoming waveform a derived waveform wherein pulses exist only in the pulse periods where no pulse exists in the incoming waveform, and means for electrically differentiating the derived waveform and applying the pulses thus obtained to the other one of the actuation inputs of the trigger stage. A device in accordance with the invention will now be described, by way of example lPrice 3 s 6 d l only, with reference to the accompanying drawings, wherein: Fig 1 illustrates a device according to the invention; Fig 2 shows the waveforms appearing at various points of the device illustrated in Fig. 1. In the device shown in Fig 1 it is assumed that the pulses of the incoming waveform each present a time length different from the time length of half the pulse period It is also assumed that the incoming pulse-modulated waveform will be leading in time with respect to the waveform which is to be obtained therefrom In addition, it is considered that the incoming waveform is available or may be adapted to be available both in its true representation and in another representation which will be called the complemental representation. The voltage levels in the true representation are always high when the voltage levels in the complemental representation are low and vice versa As will be explained the device shown in Fig 1 will deliver the waveform in both a true and a complemental representation. In Fig 2, the true representation of the incoming waveform is shown at c and has a pulse period of time length 0 The time length of any of the pulses in this waveform is shorter than & Illustratively, the waveform c may be considered as a binary encoded train of electric pulses representing the numerical quantity thirty-eight, viz 0 1 1 0 0 1 (reading this binary number from the left to the right). The complemental waveform is shown at c.

It presents a higher value of voltage whenever in the true waveform c there exists a lower value of voltage and a lower value of voltage when in the true waveform there exists a higher value of voltage The higher and lower values of voltage are, of course, the same in both the true and complemental waveforms. From the input terminal c in Fig 1, the waveform c is applied to a pulse regenerative amplifier I In this pulse regenerative amplifier SO 784,999 each pulse existing in the waveform c will be put in phase with a series of synchronisation pulses T and will be brought to a time length of 0/2 i e half the pulse period. The regenerative amplifier I shown in the drawing includes a vacuum triode tube 1 having its plate supply applied through the primary winding of a transformer 2, the secondary winding of which is so wound as to reverse the direction of the voltage variations in its primary winding The control grid of the vacuum tube 1 receives a positive bias through a resistance 8 and is connected through a unidirectionally conducting element is 6 such as a diode, to a negative bias applied through a resistance 5, on the one part, and through a similarly branched diode 7 to a terminal receiving synchronisation pulses T of rectangular waveform As shown in Fig 2, in this waveform T, higher and lower voltage levels alternate with a frequency of 1/0, each voltage level having a duration of 0/2 The anodes of both the diodes 6 and 7 are connected to the control grid of the triode 1 The negative bias applied through resistance 5 is also connected to the input terminal c through a diode 3 which is connected in a reverse direction to the diodes 6 and 7 Each pulse of the waveform c appearing in the transmission path varies between a negative potential more negative than the negative bias at 5 and a positive potential greater than the positive bias through resistance 8 Thus the diode 6 only conducts in the time intervals between the pulses of the incoming waveform c Thus each time the diode element 6 is blocked by an incoming pulse, the tube 1 conducts only if, at the same time the voltage is at its higher value in the synchronisation waveform T, for it can be seen that the lower value level in this waveform will counteract the positive bias at 8 and maintain the triode 1 in its non-conducting state Conversely, when no incoming pulse exists at C, a higher voltage value in the waveform T cannot counteract the negative bias applied through the diode element 6 to the control grid of the triode 1. Consequently the tube 1 will only conduct each time the diode elements 6 and 7 are simultaneously non-conducting This reduces the time intervals during which the tube 1 can conduct to those wherein both the signals c and T are of their higher voltage values However, it is required that, each time the tube 1 conducts, the time interval during which it will remain conducting should be equal to 0/2, the width of

any coincident pulse T To satisfy this condition, one end of the secondary winding of the transformer 2 is connected to the cathode of a diode element 4 the anode of which is connected back to the negative bias through resistance 5 When a coincidence occurs between a pulse c and a pulse T, the tube 1 conducts and the current flowing through the primary winding of the transformer 2 increases the voltage across the secondary winding In the rest condition of the regenerative amplifier, the voltage across the secondary winding of the transformer 2 is maintained at a determined value by means of 70 a suitable bias potential which acts as a clamp for the pulses thereacross When the voltage across the secondary winding increases to a positive value (which may, for instance, be determined from a positive bias applied 75 through a diode element 11 or several such elements in parallel relation receiving this positive bias upon their cathodes and having their anodes connected to the same end of the secondary winding as the anode of the diode 80 element 4), diode 4 becomes conducting and feeds back the said positive biasing voltage, to the cathode of the diode element 6 in substitution for the voltage from the input terminal c through the diode element 3, and diode 4 85 does this before the end of the input pulse. The diode element 6 is thus maintained nonconducting and the tube 1 remains conducting until the voltage T returns to its lower value and the diode element 7 again conducts 90 Thereupon, the tube 1 is blocked and the voltage across the secondary winding is brought to its lower value, the diode element 4 is blocked and the diode element 6 becomes conducting The regenerative amplifier has then 95 come to its rest condition. When the triode tube 1 is blocked, however, a reverse direction of current is set up in the primary winding of the transformer 2, and this induces in the secondary winding of the 100 transformer 2 a decrease in the voltage across its terminals which brings that voltage to a more negative value than the negative steady state bias thereof In order to avoid such a stray backswing voltage from the output of 105 the regenerative amplifier I, both ends of the secondary winding are connected to respective anodes of a pair of diode elements 9, the cathodes of which are connected to a common point which is negatively biased through a 110 resistance 10 and which is such that, as soon as the voltage across the secondary winding becomes lower than its predetermined rest voltage, these diode elements 9 are blocked. This common point constitutes the output of 115 the pulse regenerative amplifier I from which only the required positive pulses are transmitted. It is apparent that any other structure of pulse regenerative amplifier may be used, pro 120 vided the desired result is obtained.

For the waveform c the pulse regenerative amplifier I delivers a signal wave such as shown at SI in Fig 2. The waveform c of Fig 2 is applied to the 125 input terminal c of Fig 1 and to the cathode of a diode element 12, the anode of which is connected to a point which is positively biased through a resistance 31 This point is connected through a diode element 13 (connected 130 is also shown a cathode follower stage V to the control grid of which is connected the lead 29 and the finally issuing yoltage waveform C, Fig 2, will appear across the cathode load resistance 30 of this stage V Of course, such 70 a final cathode follower stage is not essential, but normally it will be provided in the case when the issuing voltage C is due to be distributed to a plurality of utilisation channels 75 The manner in which the bistable trigger stage III acts for generating the waveform C from the actuation thereof from points 15 and 18 by the pulses of the two series dl and d 2 is as follows: 80 To begin with the stage III is at rest and in the condition with the tube 20 non-conducting or blocked and the tube 21 conducting-the stage having been set to the rest position for instance from a reset voltage from a terminal 85 32 to the actuation input point 15 each time the stage III has been operated during a cycle of operation thereof The first pulse d 2, positive, is applied to the control grid of tube 21 which is on (i e conducting) This pulse does 90 not trigger the stage III which remains in its rest condition The second pulse d 2, negative, puts the tube 21 off (i e non-conducting) so that the stage III is triggered and the tube 20 is put on The voltage on the lead 29 reaches 95 a high value and in the illustrated case, this high value is that of earth potential Thus, the waveform C which has remained at its lower value during a time interval 0/2, between the first two pulses of d 2, now reaches its higher 100 value This higher value is preserved during a time interval 6 since the first positive pulse dl does not trigger the stage III and it is the second pulse dl, negative, which occurs a time interval O after the second pulse d 2, which 105 again triggers the stage III The waveform C is then brought to its lower value, a condition in which it remains for a time interval 0/2, when the third pulse dl positive, puts on the tube 20, which was off, and again triggers the 110 stage III The voltage on the lead 29 again takes its higher value for a time interval 0/2, when the fourth pulse dl, negative, turns the tube 20 off, and the tube 21 on. The third pulse d 2, positive, then reaches 115 the grid of tube 21, but does not trigger stage III The fourth pulse d 2, negative, turns off the tube 21 and again the waveform C reaches its higher value, after this waveform C had remained for a time interval O at its lower 120 value. Both the following pulses d 2 will trigger the stage III so that,

after remaining at its higher value for a time interval 0/2, the waveform C will remain for a time interval 0/2 at 125 its lower value and then will be changed to its higher value once more. It will preserve this higher value during a time interval 0 since the next fifth, pulse dl, positive, does not trigger the stage III, but the 130 in a similar direction to diode 12) to an input terminal t, which further receives the waveform t of Fig 2 in which a pulse appears in every period S Such an arrangement operates in a fashion similar to the arrangement including the diode elements 6-7 in the regenerative amplifier I: the voltage value at the common biasing point of the diode elements 12 and 13 can only be of its higher value when the voltages in the waveforms c and t simultaneously are at their higher values At this point there will thus appear a waveform c() in Fig 2 wherein, as required, there is no pulse in any pulse period 6 wherein a pulse exists in the waveform c and on the other hand there is a pulse in any pulse period O wherein no pulse exists in the waveform c. The waveform c( -) is applied to the input of a pulse regenerative amplifier II, identical to the pulse regenerative amplifier I The waveform issuing from the pulse regenerative amplifier II is shown at 52 in Fig 2. The waveform Sl issuing from the amplifier I is applied to a differentiating network, constituted by the series capacitor 14 and the resistance 16 to a fixed biasing potential so that, at the point 15 there appears the electrically differentiated signal consisting, as shown at dl in Fig 2, of a series of short pulses of alternately positive and negative polarities or directions, each of these short pulses corresponding to either a leading or a trailing edge of a pulse in the signal 51. The waveform 52 issuing from the pulse regenerative amplifier II is applied to a differentiating circuit or network constituted by the series capacitor 17 and the resistance 19 to a fixed biasing potential so that, at the point 18 there appears the electrically differentiated signal consisting, as shown at d 2 in Fig. 2, of a series of short pulses of alternately positive and negative polarities or directions, each of these short pulses corresponding to either a leading or a trailing edge of a pulse in the signal 52. The points 15 and 18 constitute the actuation terminals of a bistable trigger stage III, comprising the two tubes 20 and 21 The design of the bistable stage III is a known design and is such that the plate of the tube is connected to the control grid of the tube 21 through a network 23 including a parallel connection of a condenser and a resistance, and the plate of the tube 21 is connected to the control grid of the tube 20 through a similar network 26 The tubes 20 and 21

are triode or multi-grid tubes, and their cathodes receive a common bias through a resistance 22 This bias consists for instance of the high negative supply voltage and the plates of the tubes 20, 21 are connected to earth, through usual plate load resistors (not shown) From the plate of the tube 21 is taken an output lead 29. The issuing waveform will appear upon the output lead 29 However in the drawing there 784,999 784,999 sixth pulse dl, negative will turn off the tube and trigger the stage III. As the stage III is of a symmetrical structure, the plate of tube 20 follows a voltage change which is always the reverse of the voltage change of the plate of the tube 21 An output lead from the plate of this tube 20 will deliver a waveform C which is the complement of the waveform C This may be found to be advantageous during the operation of the device; in the rest condition, however, the waveform C thus obtained would remain at its higher voltage value and such a condition is not desired for the operation of the device. Of course, a compensation could be introduced in the circuits utilising this waveform C However, it may be advantageous to generate such a waveform C by the provision of an additional trigger stage and it is such an arrangement which is shown in Fig 1 The additional bistable stage is shown at IV and the cathode follower stage therefor is shown at VI The control actuations of the stage IV are interchanged with respect to the control actuations of the stage III: in stage IV the actuation input of tube 21 is connected through the condenser 27 to the output of the pulse regenerative amplifier I, and the actuation input 25 of tube 20 is connected through the condenser 24 to the output of the pulse regenerative amplifier II However the resetting inputs 32 of both stage III and stage IV are similarly established, for instance to the control grids of their respective tubes 20 so that the rest condition is the same for the one and the other of these trigger stages. When the incoming waveforms c and c are available with the required phase and the required width of pulses, viz 0/2, the pulse regenerative amplifiers I and II may be omitted, the input terminal c being connected to the condenser 14 and the output point of the network 12-13 being connected to the condenser 17 (for actuation of the bistabie trigger stage Ill). When the waveform c is not available, it has to be elaborated within the device and to do this, a mere polarity-changing stage may be inserted from the terminal c to the terminal c, whether pulse regenerative amplifiers need to be inserted as shown, or need not be inserted. Also, when the waveform c is not available but a pulse regenerative amplifier such as I is required, the pulse regenerative amplifier II

may be omitted and a second output winding added to the transformer 2 with an opposite direction of winding with respect to the secondary winding shown in the drawing; across this additional winding would appear a waveform 51 the complement of the waveform 51. The waveform 52 could then be obtained from waveform '51 by applying it to a diode element forming part of a network such as 12-13, the other input of which would 65 receive the waveform T. Of course, if the waveforms T and t are not available, they may be provided through suitable multivibrators However, as the devices according to the invention will be used mainly 70 in electronic computers, and more particularly for preparing records upon a magnetic recording drum or the like, such waveforms as T aid t may be considered as being available in all cases 75


* GB785000 (A)

Description: GB785000 (A) ? 1957-10-23

Improvements in or relating to sonic gas analysers


COMPLETE SPECIFICATION Improvements in or relating to Sonic Gas Analysers We, C. A. PARSONS & COMPANY LIMITED, of Heaton Works, Newcastle upon Tyne 6, in the County of Northumberland, a British Company, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: Sonic or acoustic gas analysers depend on the fact that the velocity

of sound in gases varies from one gas to another, so that variations in composition can be related to changes in velocity. In one known method a source of sound is excited electrically at a constant frequency f of several thousand cycles per second, and some of the acoustic energy is received by a microphone located at a distance d from the source. If the velocity of sound in the gas surrounding the source and receiver is V1, the finite time required for sound waves to traverse d the distance d will cause a time lag of - or an V 2adf angular lag of - at the microphone. V1 If the gas is now changed to one having a velocity of V2, the phase of the voltage at the microphone changes by 11 0=2Tdf(---) (1) Vl V2 It is not necessary to measure the absolute phase lag of the voltage at the microphone relative to that at the source, but merely the relative phase shift at the microphone as the gas mixture is varied. Normally to avoid ambiguity the phase shift is not allowed to exceed 2T. In order to measure the phase change, an electronic circuit is employed in which D.C. is caused to flow at a certain point on the A.C. wave used for exciting the source of sound, while said current is switched off at a suitable point on the A.C. wave derived from the amplified output from the microphone, or vice versa. This interrupted D.C. is passed through a meter and owing to the high frequency of interruption and inertia of the measuring instrument gives a steady deflection which changes as the value of B varies. In order to obtain accurate switching of the D.C. used for deflecting the indicating meter, the sinusoidal waves applied to the transmitter and received from the microphone are first squared and then differentiated by circuits well known to those versed in the art so that sharp pips are produced as shown in Figure 1 of the diagrammatic drawings accompanying the Provisional Specification. Owing to the magnitude and sharpness of these pips the meter indication is accurately proportional to the phase shift 0 and only dependent to an insignificant degree on the absolute magnitude of the pips. Only pips of one polarity. are used to switch D.C. on or off so that the repetition frequency of switching is f. The above means for measuring phase shifts is only given by way of an example and alternative methods may be employed.

The object of the present invention is to make the phase change B independent of temperature changes in the apparatus. If we consider the effect of a change of temperature on equation (1) it can be seen that the value of # will vary according to the combined effects of temperature on d, f, V1 and V. The effect on d can generally be ignored since the linear coefficient of expansion of the analysis tube will, in general, be negligible. The velocity of sound of all gases increases with temperature according to the equation V=VO (1 + at), where VT is the velocity of sound at T" C, V0 the velocity at 0 C. and a. is a constant 1 approximately equal to - for all gases. 600 Suppose that the frequency f of the oscillator driving the transmitter has a temperature coefficient such that fT = f, (1 + PT), where fT is the frequency at temperature T, f0 the frequency at 0 C. and P is a constant. Then (1+PT) 1 1 #=2#dfo (-)= #o when T=o (1 + aT) Vl(o) V2(o) Clearly, if P has the same sign as a and is of equal magnitude, the effects will cancel and off will be independent of temperature. The invention consists in a sonic gas analyser comprising electrically excited sound or ultra sonic vibration transmitter means, sound receiving transducer means, means for transmitting said vibrations through a variant gas and means for measuring changes in the velocity of said vibrations through said gas as a phase change between two A.C. voltages in- which analyser one or more temperature sensitive elements such as resistors inductances or capacitors is or are associated with the transmitter circuit or the receiving transducer circuit or both so as to produce a phase change which compensates for changes in the velocity of said vibrations through the gas due to temperature changes in the said gas. The invention also consists in a sonic gas analyser as set forth in the preceding paragraph in which the electrically excited sound transmitting means comprise an oscillator, which oscillator comprises resistors having negative temperature coefficients of resistance of magnitude such that the frequency of the oscillator increases in the same proportion as the velocity of sound as the temperature increases. The invention also consists in a sonic gas analyser as set forth in the first of the two preceding paragraphs in which one or more temperature sensitive resistors is or are arranged in series with a capacitance and/or inductance. The invention also consists in. a sonic gas analyser as set forth in the first or third of the three preceding paragraphs in which one or more temperature sensitive resistors is or are arranged in a circuit

adjacent to the transmitter means. The invention also consists in a sonic gas analyser as set forth in any of the first, third or fourth of the four preceding paragraphs in which those parts of the analyser subject to different temperature variation each have a circuit containing one or more temperature sensitive resistors associated therewith. The invention also consists in a sonic gas analyser constructed and arranged substantially as described hereinafter with reference to the drawings accompanying the Provisional Specification. In carrying the invention into effect in one form by way of example by virtue of the fact that the oscillator is composed of some combination of resistors, capacitors and inductances, it is possible to vary the temperature coefficient, both as regards sign and magnitude, by suitable design of one or more of these circuit elements. By way of an example in the Wien-bridge oscillator, 4#f = 1 R1R, C1 C2 where R1 and R2 are the resistances used in the circuit, and C1 and C2 the capacitances. R1 and/or R2 can be made from materials with a negative temperature coefficient such as are used for manufacturing thermistors, so that ignoring any temperature effect on C1 and C2, P in the equation fT = f, (1 + PT) is positive. The above method is suitable for those cases where the change in temperature is the same for analysis tube and for the oscillator. In an alternative method of compensation an additional phase displacement between the two sine waves is introduced by means of circuits containing temperature sensitive combinations of resistance, capacitance and/or inductance. As an example, in Figure 2(a), d represents the difference in phase between two voltages e1 and e2, which can be modified to # + # or 0- # - # by connecting a resistance/capacity network in one or other of the two circuits Figure 2(b) and Figure 2(c), where 1 # = tan-1 and # = 2#f C#R Now cot= CeRo(l + 7T), where y is the temperature coefficient of resistance of R, = 2#CRofo(1 + PT)(1 + yT) =2#CRofo[1 + (ss + ?)T] very nearly, Assuming that C is independent of temperature, di -CP+7) - 2CR0f0(P+v)sin'?= = dT 1 + C@Ro d# ss+? - can vary from ---- through zero to dT 2 P+7 - ( ) according to the value of ColoRo and 2 to which circuit the phase shift network is connected. Since the net phase difference is S+p, the d() di temperature coefficient - i--is very nearly

dT dT Q0R0(P + equal to En (ssa) + . Thus by 1 + C2zo2Ro2 choosing the correct sign and a suitable value for C,,R, it is always possible to make the dO di overall temperature coefficient i-- equal dT dT to zero. If, by way of an example, e0 1 radian, 1 di P+r p+y =2a=- and -= , 300 dT 3 3 and y=2ss-3a=a, which can be achieved easily by making the resistance R partly of a pure metal and partly of a metal with negligible temperature coefficient such as manganin. If for any reason a resistance with a negative temperature coefficient is required, a thermistor can be used, but since these components have a high temperature coefficient (about 5% per 1 C.) it will generally be necessary to use them in combination with nontemperature sensitive resistors to reduce the effect. If necessary, the phase shifting network can be mounted close to the oscillator so that both have nearly the same temperature. In this way temperature drift when the apparatus is first switched on will be reduced to a minimum. In certain cases it may be found desirable to use Ithe 'analysis tube at a distance from the electronics units, and the two component parts of the apparatus may experience different temperature variations. It is then possible to compensate for a and ss separately by employing one phase shifting circuit associated with the analysis tube and la second phase shifting circuit associated with the electronics unit. What we claim is: - 1. A sonic gas analyser comprising electrically excited sound or ultra sonic vibration transmitting means, sound receiving transducer means, means for transmitting said vibrations through a variant gas and means for measuring changes in the velocity of said vibrations through said gas as a phase change between two A.C. voltages in which analyser one or more temperature sensitive elements such as resistors inductances or capacitors is or are associated with the transmitter circuit or the receiving transducer circuit or both so as to produce a phase change which compensates for changes in the velocity of said vibrations through the gas due to temperature changes in the said gas. 2. A sonic gas analyser in accordance with Claim 1 in which tl:e electrically excited sound transmitting means comprise an oscillator, which oscillator comprises resistors having negative temperature coefficient of resistance of magnitude such that the frequency of the oscillator increases in the same proportion as the velocity of sound as the temperature increases. 3. A sonic gas analyser in accordance with

Claim 1 in which one or more temperature sensitive resistors is or are arranged in series with a capacitance and/or inductance. 4. A sonic gas analyser in accordance with Claim 1 or Claim 3 in which one or more temperature sensitive resistors is or are arranged in a circuit adjacent to the transmitter means. 5. A sonic gas analyser in accordance with any of Claims 1, 3 or 4 in which those parts of the analyser subject to different temp era- ture variation each have a circuit containing one or more temperature sensitive resistors associated therewith. 6. A sonic gas analyser constructed and arranged substantially as described hereinbefore with reference to the drawings accompanying the Provisional Specification. PROVISIONAL SPECIFICATION Improvements in or relating to Sonic Gas Analysers We, C. A. PARSONS & COMPANY LIMITED, of Heaton Works, Newcastle upon Tyne 6, in the County of Northumberland, a British Company, do hereby declare this invention to be described in the following statement: Sonic or acoustic gas analysers depend on the fact that the velocity of sound in gases varies from one gas to another, so that variations in composition can be related to changes in velocity. In one known method a source of sound is excited electrically at a constant frequency f of several thousand cycles per second, and some of the acoustic energy is received by a microphone located at a distance d from the source. If the velocity of sound in the gas surrounding the source and receiver is V,, the finite time required for sound waves to traverse the distance d will cause a time lag d 27rd f of - or an angular lag of ----- at the V1 V1 microphone. -If the gas is now changed to one having a velocity of V2, the phase of the voltage at the microphone changes by 1 1 # = 2#d f (-) ....(1) Vl V,

* GB785001 (A)

Description: GB785001 (A) ? 1957-10-23

Improvements in and relating to echo-ranging and the like


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BE544683 (A) DE1193685 (B) FR1140572 (A) NL110770 (C) US3019411 (A) FR73126 (E) BE544683 (A) DE1193685 (B) FR1140572 (A) NL110770 (C) US3019411 (A) FR73126 (E) less Translate this text into Tooltip

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PATENT SPECIFICATION Inventors: PETER ROY HOPKIN and WILLIAM HALLIDAY Date of filing Complete Specification Jan 18, 1956. Application Date Jan 25, 1955. 785 0001 No 2237155. Complete Specification Published Oct 23, 1957. Index at acceptance: -Classes 40 ( 7), DR(IC 2: 4 P 15 4 PX), D 54; and 118 ( 2), G 4 (A 2: B: D: E). International Classification: -GO 8 f I-104 p. COMPLETE SPECIFICATION Improvements in atnd relating to Echo-Ranging and the like We, KELVIN & HUGHES LIMITED, a British company, of Kelvin Works, Kelvin Avenue, Hillington, Glasgow, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement:- The present invention relates to echo-ranging and the like, that is to say systems in which pulses or bursts of waves are emitted from a transmitter, some of the wave energy is reflected as echo signals from objects in their path back to a receiver and the received echo signals are displayed or recorded upon a time base Examples of such systems are echosounding in water, flaw detection in solid bodies to be tested, and radar.

For some purposes in echo sounding it is required to scan a range of depths which is close to the sea bottom and which is only a small fraction of the total depth from the surface to the bottom An example is the detection of fish close, to the sea bottom where for example the total depth may be about 200 fathoms and the range of depths to be investigated may be of the order of one to two fathoms from the bottom. For such purposes a cathode ray tube " Ascope " presentation has been found preferable to a recorder, such as an electrolytic pen-type recorder One reason is that with the former, which operates by deflection of a spot, a greater number of discrete levels of echo intensity can be represented than with the latter, with which different echo intensities are represented by different degrees of darkening of a paper strip. Another reason is that the intensity of the spot in a cathode ray tube varies inversely as the speed of movement of the 'spot It is usually arranged that the large echo received from the bottom deflects the spot off the screen and hence with this echo the speed of the spot is high With an echo received from a fish near the bottom, on the other hand, the spot will be deflected only to a small extent and its brightness will, therefore, be relatively high. Certain difficulties, however, arise from the lPrice 3 s 6 d 1 fact that the range of depths presented on the screen is required to be only a small fraction of the total depth Thus, for instance, with a total depth of 200 fathoms, the echo time, that is the time between the emission of a pulse and the receipt of the echo, is about 500 milliseconds and the pulse repetition period employed is about the same The range scanned may, however, represent only, say, 30 milliseconds The result is that the operator viewing the screen is presented with very brief pictures of the echoes recurring at about 2 second intervals It has been found that considerable fatigue results. Moreover, because of the comparatively long interval between presentations, no two successive pictures are exactly the same, and, in particular, the range from ship to bottom has usually changed appreciably owing to the ship's motion Since the time base of the cathode ray tube is triggered in dependence upon the time of occurrence of the transmitted pulse, this means that the position of the bottom echo on the cathode ray tube display is continually shifting, thus making a comparison of successive pictures difficult. The use of a screen of high persistence is of very limited assistance since with such a screen the brightness decays rapidly to begin with, even though it may persist at a low intensity for a long time. Corresponding difficulties to those above set forth in connection with echo sounding may be met with in other like systems.

The present invention has for its principal object to provide improved echo-ranging and like equipment in which one or both of the difficulties mentioned is or are substantially reduced or eliminated. According to the present invention there is provided echo-ranging or like equipment for displaying or recording echo signals from a predetermined range of distances from a wave transmitter, the equipment comprising a display or recording device, means for triggering a time base of the display or recording device, under the control of an echo signal from a 785,001 region at the fur-ther limit of or beyond the said range, means for delaying received each signals from within the said range relatively to the said triggering echo signal by a time equal to or greater than twice the time of travel of the wave between the extremity of the said range nearer the transmitter and the said region, and means for applying the delayed signals to the display or recording device. In the case of echo-sounding, the said region may be the sea bottom and the invention is of special value when the predetermined range is near the sea bottom Since, when using the present invention, the bottom echo serves to control the triggering of the time-base, and since the delay of the received signals applied to the tube is fixed, the position on the screen of the cathode ray tube of the bottom echo remains fixed. In the case of flaw detection the said region may be the rear surface of the body under test, that is the surface opposite to that into which the waves are injected and through which they are received after reflection In radar, the said region may for example be the coastline when the equipment is being operated from aircraft or at sea. The pulses may be emitted at regular or irregular intervals and the intervals may be wholly random throughout at least over a time interval equal to twice the time of travel of the wave between the transmitter and -the said region, or may be in recurrent like groups, the intervals within each group varying in a random or regular manner. According to a further feature of the invention, the time base is arranged, between successive transmissions, to execute a plurality of sweeps and to display or record the same echo signals, suitably delayed, during each of these sweeps In this way, instead of only one picture being presented during each interval between transmitted pulses, a considerable number of like pictures can be presented thereby reducing fatigue of the operator and increasing the time during which echoes can be studied. The invention will be described by way of example as applied to echo sounding, with reference to the accompanying drawings in which:Fig 1 is a block circuit diagram of one embodiment of the invention; Fig 2 contains waveform diagrams showing the waveforms (in idealised form)

occurring at various points in Fig 1; Figs 3, 5 and 7 are block circuit diagrams of other embodiments of the invention; Figs 4, 6 and 8 show additional waveforms present in the circuits of Figs 3, 5 and 7 respectively, and Fig 9 shows waveforms occurring in another form of the invention. Like parts in the several figures have the same reference. Each of the waveforms is designated by a small letter and this letter appears in the circuit diagrams at the paint where that waveform occurs In Figs 4, 6 and 8, waveforms occurring in the circuits of Figs 3, 5 and 7 which 70 are the same as those in Fig 2 are not repeated excepting for waveform (e) which is included in order to show the time relationship between the various waveforms. Referring to Figs 1 and 2, what will be 75 called transmitter-receiver equipment is included within a broken line rectangle 10 It includes a pulse generator 11 generating pulses (a) of recurrence period 500 m S which are applied to a delay circuit 12 which may be a 80 pulse-broadening circuit producing the pulses (b) of say 5 m S duration The recurrence period chosen in this example is suitable for use up to a range of 200 fathoms without ambiguity The trailing edges of the pulses 85 (b) serve to trigger a transmission pulse generator 13 which generates a burst of oscillation of suitable frequency at each triggering, and these bursts are applied to a transducer Tx by which waves are emitted into water 90 A receiving transducer Rx receives echoes which produce an echo signal output (d) which is applied to a gain-controlled amplifier 14. The pulses (a) are fed to a muting and swept gain generator 15 which generates there 95 from the waveform (c) which is applied to the amplifier 14 to control its gain The first part 16 of the waveform (c) is designed to mute the amplifier 14 and the delay imposed by the circuit 12 is chosen to ensure that the mut 100 ing has become effective before transmission occurs Thereafter the waveform (c) increases the gain of the amplifier 14 to a maximum after about 250 m S In this way compensation is provided for the decrease in the echo amplitude 105 with range. The ewho signal (d) includes a break-through 17 of the transmitted pulse, a bottom echo 18 and a second time bottom echo 19 which is produced by the transmitted pulse reflected 110 first from the bottom, then from the surface, and again from the bottom A fish echo 20 is also shown All the components of the waveform (d) that have been mentioned arise from the same transmitted pulse 17 and later trans 115 mitted pulses give rise to corresponding components. The echo signal at terminal 21 is applied to a delay unit 22, shown within broken lines, and comprising a recorder amplifier 23 the output 120 of which is connected to a magnetic recording head 24 adapted to

record the signals upon the surface of a drum 25 of magnetic material The drum is rotated at such a speed that the desired time delay can be produced between the 125 recording head 24 and a reproducing head 26. The time delay in the present example is 10 m S and the drum 25 is therefore rotated at 3000 R P M An erase and bias oscillator 27 is also provided, in known manner, to feed 13 ( 785,001 erase oscillations to a head 28 and bias oscillations to the recording head. The signals picked up by the head 26 are amplified at 29 and fed through a gain controlled amplifier 30, whose purpose will be referred to later, to a display device 31; in this example to a Y-deflecting plate of a cathode ray tube, where they have the form and relative timing shown at (j) in Fig 2 Thus they comprise bottom echoes 181 and fish echoes ' delayed by 10 m S relatively to the corresponding parts 18 and 20 respectively of the waveform (d) It will be noted that the transmitted pulse 17 has been eliminated from waveform (j) by the muting generator 15. The signals from 21 are also applied to an amplitude gate 32 adapted to pass only the large amplitude of the bottom echo pulses 18, thus producing the waveform (e) which is fed to a time gate 33 The waveform (b) is applied from the delay circuit 12 to a waveform generator 34 adapted to generate therefrom the waveform (f) The time delay of the pulses in waveform (f) relatively to those of the waveform (b) is adjustable in the generator 34 The waveform (f) is fed to the time gate 33 to open this gate during the positive-going pulses of the waveform and the output (g) of the time gate 33 therefore has the form shown in Fig. 2 These pulses (g) serve to trigger a time base 35, which may have a working stroke of m S, to generate the time base waveform (h) which is applied to the X-deflecting plates of the tube 31 The waveform (f) applied to the time gate 33 ensures that the triggering pulses (g) correspond only to the bottom echoes 18 and not to second time bottom echoes 19. The time relationship between the waveform (j) fed to the Y-plates and the waveform (h) fed to the X-plates is seen from Fig 2 Thus the sweep of the cathode ray display represents a range of distances from the transmitter including the bottom and the fish echo. The purpose of the gain-controlled amplifier 30 is to afford compensation for variations in the amplitude of echoes due to changes in propagation conditions The waveform (g) is fed to an amplitude measuring circuit 36 which generates a control voltage dependent upon the amplitude of the pulses on the waveform (g) This control voltage is applied to the amplifier 30 in suitable sense to control its gain. It will be seen that since the time base is triggered at the time of occurrence of the bottom echo signal in the receiver and since the

echo signals displayed by the cathode ray tube are delayed in time by 10 m S relatively to the received echo signals, the echo signals received during the last 10 m S before the arrival of the bottom echo will be displayed The echoes from objects at a fixed distance from the bottom will be presented in fixed position irrespective of any motion of the ship. Suitable means are provided to rotate the recording drum 25 at a fixed speed in order that the time delay introduced may remain constants The embodiment shown in Fig 3 provides for a plurality of sweeps of the time base dur 70 ing each bottom echo recurrence period The transmitter-receiver equipment may be as shown at 10 in Fig 1 and is represented in Fig 3 by a block 10 The waveform (e) from the amplitude gate 32 is in this case fed to a 75 multi-vibrator 38 replacing the manually adjustable time gate 33 of Fig 1 and generating an output (k) (Fig 4) which controls the erase and bias oscillator 27 to generate the waveform ( 1) It also generates a waveform 80 (m) for triggering the time base 351 The multi-vibrator 38 is so constituted that it responds to a negative triggering pulse of waveform (e), to produce a negative-going edge 39 in waveform (k) and then remains unrespon 85 sive to any further triggering pulses until a predetermined time has elapsed when it produces the positive-going edge 40 The multi-vibrator is then in condition to respond to a further triggering pulse 90 The time interval between the edge 40 and the expected time of arrival of the next edge 39 is arrived at by adding the time equivalent of the possible motion of the ship, say 10 m S, to the delay between the erase and reproduc 95 ing heads 28 and 26, say 15 m S, to give a figure of 25 m S. The waveform (k) ensures that erasure and recording take place only during the intervals to 39 which in this example are of 25 m S 100 duration Thus the reproducing head 26 picks up the recorded signals a plurality of times and generates the waveform (o) The pulse PO in waveform (e) is assumed to be the first pulse and it is for this reason that the part 37 of 105 waveform (k) is shown as positive. The time base 351 is such that it is triggered by positive-going edges of the waveform (m) and, once triggered, runs freely generating a plurality of sweeps as shown at (n) until it is 110 stopped by a negative-going edge of the waveform (m) The recurrence frequency of the time base is adjusted accurately to be equal to the time of rotation of the drum 25 and the delayed echo signals (o) are then displayed a 115 number of times during each recurrence period of the transmitted pulses. The waveforms shown are of course not to scale and with a transmitted pulse recurrence period of 500 m S and a time base sweep of 12 120 m S, the number of repetitions of the echo signals will normally be much

greater than the three shown. The signals (o) are fed to a presentation device which may be a display device 41 such 125 as a cathode ray tube, or a recording device, and the time base waveform (n) is applied to produce the time base of the device. The embodiment of Fig 5, with the additional waveforms of Fig 6, provides a plur 130 785,001 ality of sweeps in each recurrence period without requiring accurate timing of a time base with the rotation of the drum. The erase and bias oscillator 27 is controlled as in Fig 3, by the waveform (k) from the multivibrator 38 in such a manner that recording and erasure takes place only during the intervals 40 to 39 in waveform (k) There is provided a further reproducing head 42 introducing a time delay of, say, 2 m S relatively to the recording head 24 The signal reproducing head 26 introduces a delay of 10 m S relatively to the head 42 and therefore of 12 m S relatively to the head 24 The head 42 -produces an output which repeats itself at each revolution of the drum 25 while erasure is prevented by the waveform (k) This output is applied to a trigger reproducer amplifier 43 whose output (p) is applied to an amplitude gate 44 Only the large amplitude of the bottom echoes can pass through the gate 44 and the output of this gate, therefore, has the form (q) which is applied to trigger the time base 35, thus producing the time base waveform (r) which is fed to the display or recorder device 41 The output (o) of the reproducer amplifier 29 is delayed by 10 m S relatively to the time of triggering of the time base and is also applied to the display or recorder device 41. In this embodiment the triggering of the time base is locked to the rotation of the drum and the display or recording sweeps can be arranged to continue over substantially the whole of the 500 m S recurrence period. The number of repetitions of the sweep that can be provided can be further increased by using the embodiment of Fig 7 using the additional waveforms shown in Fig 8 In Fig 7 much of the equipment shown in Fig 5 is duplicated and such parts are given the same references as in Fig 5 but followed by the letter A or B Thus two recording drums 25 A and 25 B are used, each in the same manner as in Figure 5. The output (e) from the amplitude gate 32 consisting only of the bottom echo pulses is applied to trigger a multivibrator 381 which generates the waveform (k) which is applied to a time gate 33 ' and opens this gate during the positive-going parts of the waveform (k) The waveform (e) is also applied to the time gate 331 and the output from this gate is the waveform (g) The waveform (g) from the time gate

33 ' is applied to a switching waveform generator 50 which generates a switching waveform (s) by which erase and bias oscillators 27 A and 27 B are rendered operative alternately, one or the other of these oscillators being always operative The signals from the transmitter-receiver equipment 10 are applied continuously to the recording heads 24 A and 24 B but are of course only operative when the corresponding erase and bias oscillator is operative. The switching signals (s) also control a trigger switch 53 and a signal switch 51 The trigger switch 53 applies the outputs of the heads 42 A and 42 B alternately to the amplitude gate 44, and the signal switch 51 applies the outputs of the heads 26 A and 26 B alternately to the display or recorder device 41 The 70 trigger signal from 42 A or 42 B and the echo signals from 26 A or 26 B is arranged to be applied from that one of the two drums 25 A and 25 B which is at any time not being erased. It has been assumed heretofore in the 75 various embodiments described that the transmitted pulses are of a constant recurrence frequency This is not necessary and, in fact, some advantages can be obtained by making the pulse intervals other than constant An 80 example will be described with reference to Fig 9. PI,P ' PG shown at (t) represent transmitted pulses at irregular intervals The bottom echo from P, is shown in waveform (u) 85 at B, and a fish echo from P, is shown at F, Echoes from subsequent pulses have the same subscript as the transmitted pulses giving rise to the echoes. A time base waveform triggered from the 90 bottom echoes B,, B of waveform (u) is shown at (v) The delayed echo signals such as DB 1, and DF, are shown at (w) and by comparison of the waveforms (v) and (w) it is seen that, assuming that the fish represented by the 95 echoes F,, F etc remain at a constant distance from the sea bottom, the fish echo will be displayed at a fixed position on the time base. Now considering an echo N, in waveform (u) from an object near the surface than the 100 fish, this gives rise to the delayed echo signals shown at (x) and it will be seen that these do not produce a fixed display on the time base of waveform (v) Thus by using transmitted pulses at varying intervals it is possible to use 105 a pulse recurrence period or a minimum time interval between successive emitted pulses, less than the echo time, and nevertheless to avoid ambiguity since only echoes within a selected range produce a stationary display 110 Instead of a drum 25 for magnetic recording there may be used other like means such as an endless tape. Other forms of delay means than the magnetic recording means described may be used 115 For instance an acoustic delay device -using a a liquid or gas, or an electrical delay network may be used Repetitions

of the signal waveform may also be obtained by repeated reflection or by feed-back 120 While transducers Tx and Rx for transmitting and receiving have been described, the invention can equally well be applied to common T/R arrangements. The values of time intervals which have 125 been referred to are, of course, given by way of example only and wide changes may be made in these. The way in which the invention can be applied to systems other than echo-sounding 130 785,001 systems will be understood by those skilled in the art.


* GB785002 (A)

Description: GB785002 (A) ? 1957-10-23

Rotor for a compressor, turbine or like fluid flow machine


PATENT SPECIFICATION Inven or: LEONAR 1 Date of filing Complete Specificati 1 t v X) D Application Date: April 20, 1955. Complete Specification Published: D) ISLIP ion: March 12, 1956. No. Oct 23, 1957. 785,002 11370/55. Index at acceptance:-Class 110 ( 3), B 2 K. International Classification:-F Old. COMPLETE SPECIFICOATION Rotor for a Compressor, Turbine or like Fluid Flow Machine We, POWER JETS RESEARCH AND DEVELOPMENT) LIMITED, of 25,

Green Street, London, W 1, a British Company, do hereby declare the invention, for which we pray that a patent may be granted to us, and, the method by which it is to be performed, to be particularly described in and by the following statement: - This invention relates to rotors for compressors, turbines and like fluid flow machines, and is concerned with the type of rotor comprising a plurality of axially successive rotor discs having annular axially abutting locating faces for centring the discs relative to one another. One method of ensuring concentricity of the discs is to provide axially extending dowels or the like fitting into holes in the locating faces It is found however that crushing of the dowels or their holes sometimes occurs and so concentricity is lost Another method is to form one disc with a cylindrical spigot fitting into a corresponding socket inm the other, but it is difficult to ensure an accurate fit if the spigot diameter is large, and moreover reassembly may not be possible due to differential centrifugal growth of the two discs. Accordingly the present invention provides a rotor for a compressor, turbine or like fluid flow machine comprising at least two axially successive discs having on their adjacent sides annular axially abutting locating faces wherein the face on one disc is formed with a circumferentially extending annular rib with oppositely tapered flanks engaging with the flanks of a correspondingly tapered groove formed in the face on the other disc. Preferably there will be a number of interengaging ribs and grooves on the two faces, and they may conveniently be in profile of the form of a truncatedx screw thread. The locating faces may be on the ends of cylindrical extensions from the adjacent sides of the discs The discs may be held together by through bolts extending axially through holes in the cylndrical extensions and' locating faces. (P Aee 3 s 6 d l One embodiment of the invention will now be described by way of example with reference to the-accompanying drawings of which: 50 Figure 1 is an axial half section of one end of a rotor for a multistage axial flow compressor. Figure 2 is a fragmentary view to an enlarged scale taken on the line II-II in Figure 55 1. Figures 3, and 4 are sections to a still larger scale on the lines III-III and IV-IV respectively in, Figure 2. As shown in Figure 1, the rotor comprises 60 a plurality of coaxial axially spaced rotor discs 1 extending transversely of the rotor axis and each having a central bore la and a row of rotor blades 2 secured to its periphery in known manner, e g by fir-tree root fixings 65 Each

disc (except the end discs of the rotor) has an integral cylindrical extension 3 from each face concentric with rotor axis and radially within the blade roots while each of the end discs has a single such extension 3 The 70 end face of each extension constitutes an annular locating face which abuts axially with the corresponding face on the end of the adjacent extension on the adjacent rotor disc. As shown in Figure 2, the extensions are 75 formed with bosses or enlargements 4 at a number of positions symmetrically disposed around the rotor axis, and the discs are held together by through bolts or tie rods 5 which extend through clearance holes in these bosses 80 These bolts merely serve to retain the discs and do not themselves have any locating function. At each end of the rotor there is provided a bearer member 6 for supporting the rotor 85 in bearings. The abutting faces of each pair of cylindrical extensions 3 are formed with annular circumferentially extending ribs or serrations 7 The flanks of each serration are tapered in 90 opposite senses and engage with correspondingly tapered flanks of the grooves between, the serrations on the other disc In axial crosssection, the serrations and grooves are of the form of a screw thread with the crests truncated to leave a clearance at the roots of the serrations with which,they engage. The engaging tapered flanks of the serrations 7 serve to take the axial loads resulting from tightening the through bolts 5, and they present a comparatively large bearing area for withstanding the radial crushing loads arising from differential expansion of the discs. The interengaging serrations 7 on adjacent discs can be machined with mating form tools and, will thus fit together accurately If after running it is found that differential expansion of adjacent discs has occurred, the tapered flanks of the serrations will still allow the discs to be forced together on re-assembly while maintaining concentricity. The form of the serrations may correspond to any screw thread of generally triangular form, e g Whitworth, Acme, etc The pitch and number of the serrations will depend upon the loads to be withstood and the amounts of differential expansion of the discs 'to be allowed for Thus, the pitch of the serrations should be greater than the maximum radial differential expansion which is expected to occur

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