US2016264A

US2016264A - Multistage filter

Info

Publication number: US2016264A
Application number: US730565A
Authority: US
Inventors: Ludwig W Blau
Original assignee: Standard Oil Development Co
Current assignee: Standard Oil Development Co
Priority date: 1934-06-14
Filing date: 1934-06-14
Publication date: 1935-10-01
Anticipated expiration: 1952-10-01

Description

Oct. 1, 1935. L, w, BLAU 2,016,264

I MULTISTAGE FILTER I Filed June 14, 1934 1A E A? A265 Patented Oct. 1, 1935 Ludwig W. Blau, Houston,

Tex., assignor to Standard Oil Development Company, a corporation of Delaware Application June 14, 1934, Serial No. 730,565

10 Claims. (01. 178-44) This invention relates to improvements in a multi-stage filter.

It has been known how to combine electric networks so as to render them frequency selective; thus it is possible to make low pass filters, high pass filters or intermediate pass filters. Such a filter is the subject of applicants copending application U. S. Serial No. 659,822, entitled Method and apparatus for eliminating low frequencies, filed May 6, 1933.

When filters are to be included in electrical recording systems where high accuracy is required, it becomes necessary to damp out all oscillations originating in the filter itself. Thisis done successfully in the filter which is the subject of the above mentioned patent application. However, the introduction of damping renders the cut-off of the filter less sharp so that more stages must be added to make up for it. This means that the filter becomes larger and more expensive to construct. The invention which is the subject of this application permits of building a damped filter of a few stages with a sharp cut-off heretofore obtained only by using many stages.

The invention will be fully understood from the following description takenin connection with the accompanying drawing in which latter Fig. l is a diagrammatic representation of a preferred form of circuit;

Fig. 2 is a diagrammatic representation of a modified form of circuit, and

Fig. 3 is a diagrammatic representation'of an arrangement of apparatus for use in reflection shooting.

Referring particularly to Fig. l of the drawing, reference numeral I designates an input impedance and numeral 2 designates an output impedance. An electric circuit connects the impedances. A plurality of groups of stages of parallel branches 4, 5 and 6 are provided in the circuit. Each group or stage includes a branch A having an inductance 9, a condenser I0 and a resistance ll of a choke coil. Each group or stage also includes a branch B having a resistance I3 and a condenser I4 connected in series. A condenser I6 is provided in the circuit between the resistance l and the branch A of the stage 4, and a condenser I! is provided in the circuit betweenthe branch B of the stage 6 and the output resistance 2. A damping resistance l9 and a condenser 20 are connected in series in the circuit betweenthe adjoining stages 4 and 5. A damping resistance 2| and a condenser 22 are disposed in the circuit between the adjoining stages 5 and 6.

The circuit operates as follows: Such values of the inductance 9 and condenser Ill of the branch 7 l are selected that the combination resonates 5 at, for example, five cycles. The combination of inductance 9 and condenser Ill in series and condenser I4 in parallel are tuned to resonate at, for example, approximately 30 cycles. Then at a frequency of five cycles the voltage across the 10 inductance 9 and condenser H1 in series will be zero. In other Words, any frequency of five cycles impressed upon the input resistance I. will be practically eliminated by the branch A. On

the other hand, at 30 cycles the inductance a 1'5 and condenser 10 in series will resonate with the condenser M in parallel, and the voltage transmitted across the combination of branches A and B therefore be very high. This combinav tion of elements results in passing the waves of 20 30 cycle frequency impressed upon the input resistance l practically without attenuation through stage 4.

Referring to stage 5, the inductance 9 and condenser ID in series are tuned to resonate at, 25

for example, 10 cycles. The combination of inductance 9 and condenser Ill in series of branch A togetherwith the inductance M in parallel of branch B is tuned to resonate at 30 cycles. Then any 10 cycle frequency impressed upon the input 36 resistor I will set up practically zero voltage across the inductance 9 and condenser Ill of stage 5. In other words, any frequency of 10 cycles impressed upon the input resistance I will be practically eliminated in branch A of stage 5. At 30 35 branch A of this stage may be tuned to resonate at, for example, 15 cycles, whilethe parallel combination comprising inductance 9 and condenser ill in series of stage 6 due to an impressed frequency upon the resistor l of 15 cycles will be practically zero, so that any 15 cycle frequency will be practically eliminated. On the other hand, since theparallel combination tunes at 30 cycles any frequency of 30 cycles impressed upon the input resistor I will set up a high voltage across the combination and will therefore be 6 5" prises the parallel branches A and B as previ ously described.

Referring particularly to Fig. 3, .a preferred '7 arrangement of apparatus for reflection shooting is shown in which reference numeral 28 designates the coil of a magneto-electrical seismograph such as is describedin the copending application Serial No. 626,132 of Ludwig W. Blau et a1, entitled Seismograph, filed July 29, 1932. The coil 28 is connected across the grid and" filament of a vacuum' tube" 29 which may be a three electrode. or screen grid tube. The vacuum tube 29'is connected to the input resistance I of the circuit previously described in connection with Fig. 1. The output resistance 2 of the circuit is connected to a vacuum tube amplifier 30' which in turn isconnected to an oscillograph 3! which records the seismograms. Preferably the filter circuit is connected aheadof the amplifier 30 so that the objectionable low! frequencies can be eliminated before being amplified.

In the circuits described, the resistances I3 in branch Bof each stage of the filter function to damp out oscillations set up in the parallel combination formed by the two branchesA and B of each stage. Without the resistors I3 0b-' noxious oscillations originating in the respective stages would appear in the form of voltages across the output resistor and would therefore be passed on. This would 'be detrimental to the quality of the seismogram since great 'care must always be taken to record the filtered earth motion as faithfully as possible and' to have no ex-' traneous frequencies on the seismogram originating in the filter or any other parts of the seismograph apparatus. These extraneous frequencies would lead to misinterpretations of the results.

The resistors 19 and 2| are likewise damping resistors designed to damp out oscillations of the following circuits. The resistor l9 damps out oscillations in the circuit consisting of inductance 9 and condenser ID, of branch A of stage 4, condenser l0 and inductance 9 of branch A of stage B, and condenser 20 which lies between these stages. The resistor 19 also damps out oscillations in the circuit which comprises inductance 9 and condenser I E! of branch A of stage 5, the condenser I4 of branch B of stage 4 and the condenser 20. The resistor l9 also damps out oscillations in the circuit comprising inductance 9 and condenser IQ of branch A of stage 6, condenser M of branch Bof stage 5 and condenser 20. The damping resistor 2I damps out oscillations in the circuit comprising inductance 9 and condenser ll] of branch A of stage 5, condenser H! of branch A'of stagefi and condenser 22. The resistance 2| damps out also oscillations in the circuit comprising inductance 9 and condenser ID of branch A of stage 5, the condenser I4 of branch B of stage 6 and condenser 22. tions in the circuit comprising condenser [4 of The resistor 2| damps out oscilla- I branch B of stage 5, inductance 9 and condenser ID of branch A of stage 6 and condenser 22. The input resistor I damps out oscillations originating in the circuit comprising the condensers i6 and In in the inductance 9. The output resistor 2 damps out oscillations originating in the circuit comprising the condenser H and the inductance l3 and condenser M of branch B of stage 6.

By reason of the parallel combination 'of branches as described which may be arranged to tune at any predetermined frequency, which in the case described has been assumed to be 30 cycles, this filter will pass all or practically all energy impressed upon the input with frequency equal to or greater than 30 cycles. The filter here described therefore has a much sharper cut-oif with a smaller number of stages than has. heretofore been possible to attain. This filter renders possible the practically complete elimination of all frequencies below any certain predetermined cut-off frequency, while passing all energy or practicallyall energy of frequency higherth'an the cut-off frequency which is impressed upon the input resistance 1 or the transformer 24. i 1

Various changes may be made within the scope of the appended claims in which it is desired to claim all novelty inherent in the invention as broadly as the prior art permits.

Iclaim:

1.. A filter, 'compri'sing'an electric circuit having a plurality of stages, each stage including a branch having a condenser'and an inductance connected in series and tuned to a given frequency, the corresponding branch of each stage being tuned to different frequencies whereby these frequencies are eliminated,'each stage in cluding a branch having a condenser, the two branches of each stage being tuned to resonate together at a given frequency whereby this frequency is passed through the filter.

2. A filter, comprising an electric circuit having a plurality of stages, each stage including a branch having a condenser and an inductance connected in series and tuned to resonate at a' given frequency, the. corresponding branch of each stage being tuned, to different frequencies whereby these frequencies are eliminated, each stage including a branch having a condenser, D

the two' branches of each stage being tuned to resonate together at the same frequency outside of the range of, the first mentioned frequencies whereby this frequency is passed through the filter.

3. A filter, comprising an electric circuit. having a plurality of stages, each stage including a branch having a condenser and an inductance connected inseries and tuned to resonate at a given frequency, the corresponding branch of each stage being tuned to different frequencies whereby these frequencies are eliminated, each stage including a branch having a condenser, the two branches of each stage being tuned to resonate together at the same frequency outside of the range of the first mentioned frequencies whereby this frequency is passed through the circuit and a damping resistance in the circuit between adjoining stages for damping out the natural frequencies of the filter. I

4. A filter, comprising an electric circuit having 70 each stage being tuned to different frequencies whereby these frequencies are eliminated, each stage including a branch having a condenser and a resistance connected in series, the two branches of each stage being tuned to resonate together at a given frequency outside of the range of the first mentioned frequencies whereby this frequency is passed by the filter, and a damping resistance in the circuit between adjoining stages for damping out the natural frequencies of the filter.

5. A filter, comprising an electric circuit having a plurality of stages, each stage including a branch having a condenser and an inductance and a resistance connected in series and tuned to a given frequency, the corresponding branch of each stage being tuned to different frequencies, each stage including a branch having a condenser and a resistance connected in series, the two branches of each stage being tuned to resonate together at a given frequency, and a damping resistance for damping out the natural frequencies of the filter and a condenser in the circuit between adjoining stages.

6. A filter, comprising an electric circuit having a plurality of stages, each stage including a first shunt arm having a condenser, an inductance and a resistance connected in series, and a second shunt arm having a condenser connected in parallel with the first shunt arm, the first shunt arm of each stage being tuned to different low frequencies whereby these low frequencies are eliminated, the second shunt arm of each stage being tuned with respect to the first shunt arm of that stage to resonate at higher frequencies whereby the higher frequencies are passed.

'7. A filter for eliminating low frequency waves, comprising the inductance coil of a seismograph connected across the grid and filament of a vacuum tube, an input impedance connected to the plate resistor of the vacuum tube, an output impedance, an electric circuit connecting the impedances and including a plurality of stages of parallel shunt arms, each stage including a first shunt arm having a condenser, an inductance and a resistance connected in series and a second shunt arm having a condenser connected in parallel with the first shunt arm, the first shunt arm of each stage being tuned to different low frequencies whereby these low frequencies are eliminated, the second shunt arm of each stage being tuned with respect to the first shunt arm of that stage to resonate at higher frequencies whereby the higher frequencies are passed, a vacuum tube amplifier connected to the output impedance, and an oscillograph connected to the amplifier.

8. A filter for eliminating low frequency waves, comprising the inductance coil of a seismograph connected across the grid and filament of a vacuum tube, an input impedance connected to the plate resistor of the vacuum tube, an output impedance, an electric circuit connecting the impedances and including a plurality of stages, each stage including a branch having a condenser and an inductance and a resistance connected in series and tuned to a given frequency, the corresponding branch of each stage being tuned to different frequencies, each stage including a branch having a condenser and a resistance connected in series, the two branches of each stage being tuned to resonate together at a given frequency, a damping resistance for damping out the natural frequencies of the filter and a con-' denser in the circuit between adjoining stages, a

vacuum tube amplifier connected to the output impedance and an oscillograph connected to the amplifier.

9. A filter for eliminating low frequency waves,

comprising the inductance coil of a seismograph connected across the grid and filament of a vacuum tube, an input impedance connected to the plate resistor of the vacuum tube, an output impedance, an electric circuit connecting the impedances and including a plurality of stages of parallel shunt arms, each stage including a first shunt arm having a condenser an inductance and a resistance connected in series and a second shunt arm having a condenser and a resistance in series, the latter shunt arm being connected in parallel with the first shunt arm, the first shunt arm of each stage being tuned to different low frequencies whereby these low frequencies are eliminated, the second shunt arm of each stage being tuned respectively to the first shunt arm of that stage to resonate at higher frequencies whereby the higher frequencies are passed, a condenser connected between the input impedance and the first shunt arm, a condenser connected between the last shunt arm and the output impedance, a vacuum tube amplifier connected to the output impedance and an oscillograph connected to the amplifier.

10. A filter for eliminating low frequency waves,

comprising the inductance coil of a seismograph connected across the grid'and filament of a vacuum tube, an input impedance connected to the plate resistor of the vacuum tube, an output impedance, an electric circuit connecting the impedances andincluding a plurality of stages of parallel shunt arms, each stage including a first shunt arm having a condenser and inductanceand a resistance connected in series and a second a shunt arm having a condenser and resistance connected in series, the latter shunt arm being connected in parallel with the first shunt arm, the first shunt arm of each stage being tuned to different low frequencies whereby these low fre quencies are eliminated, the second shunt arm of each stage being tuned with respect to the first shunt arm of that stage to resonate at higher frequencies whereby the higher frequencies are 7 passed, a condenser and resistance in series connected between the input impedance and the first shunt arm, a condenser and resistance in series 7 connected between the last shunt arm and the output impedance, a vacuum tube amplifier connected to the output impedancaand an oscillograph connected to the amplifier.