US2682034A - Sity electrical pulses to crystal - Google Patents

Description

June 1954 H. c. TORREY ET AL ,0 4 I APPARATUS FOR APPLYING HIGH-INTENSITY ELECTRICAL PULSES T0 CRYSTAL RECTIFIERS Filed Jan. 15, 1946 FIG. 3

TIME

aw f (9 INVENTORS HENRY C. TORREY JEROME B. WIESNER ATTORNEY Patented June 22, 1954 APPARATUS FOR APE'LYING HIGH-INTEN- SITY ELECTRICAL PULSES TO CRYSTAL RECTIFIERS Henry C. Torrey, Cambrid B. Wiesner, Dearborn,

ge, Mass, and Jerome Mich, assignors, by

mesne assignments, to the United States of America as represented by the Secretary of the Navy Application January 15, 1946, Serial No. 641,351

8 Claims.

This invention relates to electrical test equipment and more particularly to apparatus capable of subjecting various types of electrical apparatus to a high intensity electrical pulse of predetermined energy content.

Subjecting electrical equipment to electrical surges involves specialized apparatus, the design of which depends upon the particular equipment to be subjected to the electrical surges. The principles of the present invention are herein disclosed in connection with the laboratory and production testing of cartridge-type crystal rectifiers.

In the. manufacture of cartridge-type crystal rectifiers, numerous and extensive tests are made before the unit is marketed, which tests result in a substantial increase in total cost. In pulsed radio frequency systems, impairment and failure of the crystal is usually caused by the application thereto of a voltage pulse or spike of very short time duration, often less than 0.01 microsecond. In such a short time, the crystal and the whisker contactor are unable to conduct the dissipated heat away from the contact. It has been observed'that the resulting temperature is essentially proportional to the total energy in the spike rather than its peak power. For this reason, if a pulse energy test is made before the other required tests, the unit cost of manufacture can be considerably decreased and the crystal reliability increased.

An object of this invention is to provide a device for applying pulse energy to a cartridge-type crystal rectifier or similar electrical equipment.

Another object of this invention Is to provide a device for applying pulse energy to a cartridgetype crystal rectifier of simple mechanical construction, efiicient operation and which is readily maintained.

These and other objects will be apparent from A a careful consideration of the specification and the accompanying drawings in which:

Fig. 1 is a longitudinal,cross-sectional view of a preferred embodiment of the present invention;

Fig. 2 is a graph showing certain voltage-time relationships existing in the apparatus of Fig. 1; and

Fig. 3 is a cross-sectional view taken along axis 3-3 of Fig. 1.

Referring more specifically to the drawings, IS

Fig. 1 shows a coaxial line Ill, of length I, whose characteristic impedance is substantially equal to the impedance of the crystal to be tested, and which consists of a substantially cylindrical outer conductor II externally threaded at one end, and

7 polished. A dielectric sleeve I 1,

an inner conductor I2. Two insulating bushings I8 and 28, similarly constructed, are secured within outer conductor II by small dielectric pins 26 placed in small holes drilled through outer conductor II and into bushings I8 and 28, as shown in Fig. 3. These bushings I8 and 28 slidably support and electrically insulate the inner conductor I2. Bushing I8, located near the un-- threaded end of outer conductor II, also acts as a stop for inner conductor I2 and thus, an adjacent metal flange I3 is silver soldered to outer conductor I I for further support. An internally threaded metal cap 24. which engages the correspondingly threaded end of outer conductor II, is drilled at its center and fitted with end fingers 21 to releasably hold a cartridge-type crystal rectifier 3B. The crystal cartridge 30 has a metal base Si and a metal prong 33 separated and insulated by a ceramic case 32 which also houses the crystal and the contacting whisker. The end fingers 2'! hold the ceramic case 32 in such a manner that the metal base 3I and the outer conductor II are in electrical contact and the metal prong 33 extends centrally into the outer conductor II. A metal sleeve 23 is attached to the prong 33 of the crystal cartridge 38 by fingers 29 extending from one'end of the sleeve. A fiat metal contact 22 is soldered to the end of sleeve 23 opposite the fingers 29. The fingers 29 fit securely over the prong 33 to provide good electrical contact thereat. A contact I4, hernispherically shaped to minimize capacity and high potential gradients, is fitted into the end of inner conductor I2 adjacent to the'flat contact 22 and secured by a metal contact plug I9. The contacts I4 and 22 have a metal base and are covered with a very hard shock-resistant material, such as osmium-rhodium, which is ground and internally threaded at both ends, mechanically connects and electrically insulates a core rod or plunger I5 of a solenoid 43 from inner conductor I2. Thus, the core rod [5 threaded at one end thereof engages a metal coupling I6 which is in turn threaded and engages one end of the dielectric sleeve IT. A metal plug 2|, externally threaded, which slides over the end of inner conductor I2 and silver soldered thereto, screws into the other end of the dielectric sleeve IT. The inner conductor I2 and the coupling I6 are electrically connected by a resistor 25 and a helical spring 20 located inside the dielectric sleeve I1, the resistor 25 being soft soldered at one end to the plug 2I, and in contact at the other end with the helical spring 20 which in turn is soldered to the coupling I6.

In actual operation the device is usually vertically mounted with core rod l at the top. A solenoid 43 is energized causin core rod l5 and inner conductor [2 to rise a predetermined distance. The metal sleeve 23 is fitted over the metal prong 33 of crystal cartridge 38 and this latter assembly inserted into the end fingers 21 of the cap 24 so that flat contact 22 is directly beneath and in line with hemispherical contact M. The coaxial line is charged to a voltage V by connecting a voltage source 44 directly to outer conductor II and indirectly to inner conductor l2 through resistor 25. Resistor has a very high resistance value limiting the output current from the voltage source '44 during discharge and making the upper end of coaxial line !0 appear open-circuited. When the solenoid 43 is deenergized, inner conductor l2 drops very rapidly, initially to prevent field emission, engages contact I4 and 22, forces crystal cartridge from the end fingers 21 of the cap 24 and final ly comes to rest when plug 2| meets dielectric bushing 18. When contacts I4 and 22' are engaged the energy stored in coaxial line 10 is discharged through .and absorbed by the crystal in crystal cartridge 30.

It is generally known that when a uniformly charged transmission line is discharged at one end into a load which has the same impedance as the characteristic impedance of the line, a pulse of electromagnetic energy will flow at a voltage equal to one-half the voltage across the line for a period of time equal to twice the length of the line divided by the velocity of the wave in the line.

The wave shape shown in Fig. 2 is that which would be obtained from an ideal match between the characteristic impedance of line Iii and the impedance of the crystal in crystal cartridge 30. The voltage of the pulse is shown as one-half of the voltage V of the voltage source 44, while the time duration of the pulse is shown equal to twice the length l of the line H) divided by the velocity of the wave in the line, which is a constant c for any given line. A mismatch would. result in an initial pulse whose voltage is slightly more or less than one-half the voltage of the voltage source 44, depending on the direction of the mismatch, which initial pulse would be followed by additional pulses of diminishing vo1t- However, the total energy absorbed by the crystal would remain the same, The energy absorbed by the crystal is found by taking the square of one-half of the voltage of the voltage source 44, multiplied by the time duration of the pulse and dividing this by the impedance of the crystal. This absorbed energy is usually expressed in ergs.

After the cartridge-type crystal rectifier has been subjected to pulse energy, other and known means are used to determine whether or not the crystal has been impaired.

Thus it may be readily seen that a specified amount of energy may be imparted to a cartridge-type crystal rectifier in a specified time by this invention by merely regulating the length l of the coaxial line and the voltage V of the voltage source 44. It is further seen that this energy is applied with a minimum of contact chatter and mechanical shock.

This invention is to be limited only by the appended claims.

What is claimed is:

1. Apparatus for applying pulse energy to an electrical device comprising, a transmission line, said transmission line comprising two conductors and having a characteristic impedance substantially equal to the impedance of said electrical device, one of said conductors of said line being movably disposed relative to the other or said conductors, means for conductively connecting an electrical devce to one of said conductors, a voltage source for charging said line, and means for rapidly moving said movable conductor in a direction to connect conductively said electrical device across said transmission line, whereby energy stored in said line is imparted to said electrical device.

2. Apparatus for applying pulse energy to an electrical device comprising, a transmission line, said line comprising two conductors, one of said conductors being movably disposed relative to the other of said conductors, a voltage source for charging said line, means for connecting an electrical device to one of said conductors in such a manner that when movement is imparted to said movable conductor said device is connected across said line and the energy stored in said line is imparted to said device, and means for moving said movable conductor.

3. Apparatus for applying pulse energy comprising a section of coaxial transmission line of predetermined length, the inner conductor being slidably disposed relative to the outer conductor, contact means mounted on said inner conductor, means mounted on said outer conductor adapted to releasably connect a conductive electrical device to said outer conductor, means for electrically charging said coaxial line through a resistor carried by said inner condoctor, and means for rapidly moving said inner conductor to advance said contact means toward said connecting means mounted on said outer conductor, whereby an electrical device releasably connected to said outer conductor is conductively connected across said line by said contact means and the energy stored in said line is imparted to said electrical device.

4. Apparatus comprising a section of coaxial line of predetermined length and of predetermined characteristic impedance, the inner conductor being movably disposed relative to the other conductor, means for charging said coaxial means for rapidly moving one conductor relative to the other conductor, and means mounted on said conductor adapted to discharge the energy stored insaid line across an external load upon movement of said one conductor.

5. Apparatus for applying pulse energy to an electrical device comprising a section of coaxial transmission line of predetermined length, the characteristic impedance of said line being equal to the impedance of the electrical? device to which pulse energy is to be applied, means for electrically charging said coaxial line, means for moving one conductor of said line relative to the other conductor of said line, and means mounted on the conductors of said line adapted to impart the electrical charge on said line to an electrical device upon movement of one of said conductors.

6. Apparatus comprising a section of coaxial transmission line of predetermined length and predetermined characteristic impedance, means mounted on one of said conductors adapted to releasably secure an electrical device to said conductor, means for electrically charging said mined length, the characteristic impedance of said line being equal to the impedance of the rectifier to which pulse energy is to be applied, said coaxial line comprising an outer conductor and a slidable inner conductor, means for electrically charging said coaxial line through a resistor carried by said inner conductor, means for rapidly moving said inner conductor relative to said outer conductor, and means secured to said conductors adapted to impart the electrical charge on said line to a cartridge type crystal rectifier upon movement of said inner conductor.

8. Apparatus comprising an electrical device, a transmission line, said transmission line comprising two conductors and having a characteristie impedance substantially equal to the impedance of said electrical device, one of said conductors of said line being movably disposed relative to the other of said conductors, means for conductively Xconnecting said electrical device to one of said conductors, a voltage source for charging said line, and means for rapidly moving said movable conductor in a direction to connect conductively said electrical device across said transmission line, whereby energy stored in said line is imparted to said electrical device.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 1,944,211 Brodie Jan. 23, 1934 2,108,637 Bartgis Feb. 15, 1938 2,255,898 Robb Sept. 16, 1941 2,406,405 Salisbury Aug. 2'7, 1946 2,407,847 Peterson Sept. 1'7, 1946 2,411,140 Lindenblad Nov. 12, 1946 2,459,849 Stateman Jan. 25, 1949

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