H W :; IN N 133 625. _' 2:1: m “‘1 EC WEEK FOR 243.0% 'w‘O‘iEAGE E‘UISES maxi-s ‘10-: its B33235 af 33. 3: ME CHEGAK ‘51.ij u..." 333 b 3"“...th #535 2,.“ $ 594? IIIIIIIIIIIIIIIIIIIIIIIIIIIII IIIIIIIIIII III II 3 1293 017749 LIBRARYJ Michigan State University This is to certify that the thesis entitled AN ELECTRONIC TIMER FOR HIGH VOLTAGE PULSES presented bg Parnell Marc has been accepted towards fulfillment of the requirements for fin :S_' *degree in__ 1311331133 Mew Major professo Date- 23nd-_JJme 19le 35-795 A:h . l a? . . .a 5 ' ' l ‘ , “00.13193 01“ TIES murmur ARE MAE-ABLE 01»: MICROFIIM BI cm. 1. ”me ~ AIRJOCUMBN’IS DIVISION, DITELLICENCE T-2, AIR mmmimmmm‘f‘ '- mm _ , TSAMD-aa -. " ' ’ ‘ REQUES . mm ATI no. 14697 ' cue/6H7“ FIELD - 04 yroN , Omo PLACE IN REI'URN Box to remove this chedtout from your record. To AVOID FINE retum on or before date due. ~ MAY BE RECAUE with earlier due date if requested. DATE DUE DATE DUE DATE DUE - AN ELECTRONIC TIMER FOR HIGH VOLTAGE PULSES b7 Parnell Here A mule flubnitted to the Graduate School of Michigan State College e! Agriculture and Applied Science in partial fulfilment of the requiremente for the degree of “SEER 01' SCIENCE Deperhent of Phys ice 19*? ACKNOWMENT I wieh to expreee my eincere thank: to Dr. I. H. Oegood and Dr. R. B. Bowereox whoee eug- geetione and criticieme have been eo instrumental to no in carrying out my researchee and in the writing of thie paper. I aleo wieh to expreee w an appreciation to Michigan State College. 1'he echolarehip I received tron it as well ae the ef- ficient eupport it provided me have enabled me to increase to a great extent w knowledge in phyeical ecience. m 0F CON‘EENTS Introduction................ Deeoription and Operation of the Apparatus . . The Blocking Oeoillator . . . . . . . . . . . . Calculation of I. . . . . . . . . . . . . . . Kealurenent of I . . . . . . . . . . . . . . . ThePowerStrpply............... Stability of the Apparatue . . . . . . . . . . Probable Caueee of Inetability . . . . . . . . Biblimw O O O O O O O O O O O O O O O O O 55" mmm-«wmrmw INTRODUCTION Pnleee can be defined an eucoeeeion of currentsvarying in a very ehort tine. It ie to be pointed out that an extoneive nee of pnleee haa been node in the pioneer work in radio comicatione. I The enbeequent development of electronic tubee led to the diecard of the palace. New propertiee and ueee have been found for the. and a new field of radio engineering. radio location. ie band on the production of eharp pnleee by electron tubee. they aleo have been applied to any other electronic devicee. In the preeent work. a blocking oscillator ie made nee of in order to produce a enoceeeion of eharp pnleee regularly epaoed in tine to control the action of a thyratron. hie thyratron iteelf controle the dieoharge of a capacitor through the prinary of a apart coil. Such a eyeten in to be need in the laboratory in connection with a free fall apparatne. be old apparatne naing a tuning fork gave irregular aparlre. It ie hoped that the electronic apparatus will give more regularly epaoed eparke. 131-9ch10! AND OPERATION OF THE APPARATUS The different conponente of the apparatus are a) the apart coil: b) the thyratron circuit: c) the blocking oacillator; d) the power suppli. aa indicated in.ligure l. me apart: coil has the following characteristice. Ite prilary baa an inductance of 2.56 nillihenriee with a Q of 9 for a frequency of 1.000 cyclee. Ite eecondary has an inductance of 26 henriee with a Q of 16.5 for a frequency of 1.000 cyclee. ‘ i'he epark coil ie energized by the diecharging action of the capacitor through ite primary and the thyratron, thie capacitor being charged during the non-conduc ting time of the thyratron. A General Electric 1'0 57 thyratron wae need. It etande a peak plate potential of 1.000 volte with a peak plate current of 15 anperee. he filament of the tube required l4.5 amperee at 5 volte and the control grid waa kept at -1I5 volte by neane of a battery. ' me high negative biae ie constantly applied to the grid of the thyratron. It conetitutee the fixed component of a total biae the variationa of which will control the firing of the tube. The fixed biae ie ohoeen eo that the tube cannot conduct when no other potential ie applied to the grid. 1 voltage pulee ie aleo eupplied to the grid in eeriee with the fixed biae. hie pulee ie fro- the output of a blocking oecillator which ie an important part of the circuit. Izou xmgm Z4545 XuSm _ .0: >5an $38 225 $8558 ZOKZSE 0228a I L Er Z 2% m. t . lab if .m .>m¢ M g 25 35.... o I. _ m. I: m _ LL 5mm... -3 2:4ng memoumEE wgsa : ..=ou Xxgw our. N ".0 r fi— M 05‘! l? NN EM.» in \L .82 more I_. m3 h. When the reeultent biae ie above the critical firing biae voltage which ie determined by the value of the plate voltage. the thyratron conducte until the plate potential fella below the value neceeeary for conduction. m BLOCKING OSCILLATOR Since there ie no grid biae. the tube begine to conduct ae econ ae the circuit is cloeed. Ede plate current begins to increaee. At the acne time. an LMJ'. will be induced in the grid coil. which coil is ac arranged ac to make the grid and poeitive. fhe reeult ie that the plate current increaeee; lbthen increaeee until the aaturation ie reached for the plate current. capacitor 0 he become charged during thie tine by the grid current (Iigure 3 and '4‘ . At thie nonent. eince there ie no aore voltage induced in the grid coil. the capacitor 0 begine to diecharge through a. The grid tende to become leee and leee poeitive. Then the plate current will begin to decreaee and in the grid circuit a voltage will be uprooted in the Oppoeite direction. rhi- neane that the grid are! of O tende to becone acre and more poeitive '(l'igure . 5. 6 ). Ihecut off point ie econ reached ae 6 ie diecharging 1,. trill riee above I bb and a alight oecillation nay occur which depende chiefly on the inductance of the plate coil. One eurge of 1]) ie attained which inducee the output pulee in the third winding. A new cycle of operation ie repeated ae econ ae the voltage acroee 2 ie above cut off. FIG.4 c0 52 Li. if” a ‘_ a .0; 9+ 2% ME: oz< 0} £22 835% a a: + O he E I. uzzto Se , m2: 02.53028 6. It is then understood that the thyratron fires wherever there is a variation of mgnetic field through L1. file negative parts of the pulse occur each tires the thyratron is conducting. he interval 2 between successive pulses depends ee- sentially on: 1) the cut off of the triode: 2) the voltage to which the capicator 0 is charged: 3) the product 1' 3 BO called the tine constant of the blocking oscillator. CALCULATION 01' I. It would be very instructive to derive a formla giving the interval 1' between pulses according to the Char- acteristics of the blocking oscillator. lo rigorous treatment of this problen has been made. The principal difficulty lies in the fact that it is quite impossible to draw an adequate equivalent circuit for the blocking oscillator on account of the nultiple re- fledtive inductions taking place by the special three winding trans- feraers used in the circuit. An elementary approach to the question consists in supposing negligible tin different coefficients of nutual induction and to neglect also in the series circuit made of G. R, L1 the value of L1 since it is found very small in comparison with the value of n which is of the order of 105 ohm c g .02 nfd. Let em be the cut off value of the tube for the operating conditions, I" the voltage across 0 when completely charged. 'cc c Then i. v, 6""ch r . -RGLOg. T 7. The characteristics of the 6J5 show that 'co : 25Y 1°? 'bb ' WV 'c probably depends upon 3 and is approximately equal to -60 volts. HELSURMM‘ or T It has not been possible to measure 7° on account of the fast successive charging and discharging of the capacitor. But a direct neasurenent of I has been obtained by comparison by the means of the cathode ray oscillogrsph of the frequency of the pulse with the frequency produced by an audio oscillator. RESULTS OF THE ELEMENTS l 1' sec 2 flag 1/23 1 Meg 1/61 750 1 1/121; 500 1: 1/176 TEE 1°0th SUPPLY The power supply presents no special features, however. a special transformer is necessary to supply the heating power to the filament of the thyratron which requires approximately a current of 5 amps. at a potential difference of 5 volts. STABILITY 01' THE APPARATUS The principal advantage expected from this apparatus is that it will keep as constant as possible the interval between pulses during a whole laboratory period (a maximu- of 2 hours). PROBABLE CAUSES OF INSTABILITY a) The variations of the power source If the high voltage source of the power supply undergoes some fluctuations. a displacement of the operating conditions of the apparatus is inevitable. This can be prevented by adding a regulator to the power supply (YR - 150 for example). Oocassional checks of the fixed bias of the thyratron will also be necessary. b) Variations which may occur from the aging of the tubes. faking at first the case of the triode, it has bean seen that the period ‘1‘ depends on the cut off value of the 6J5 for the operating conditions. i'his on the other hand, depends on the inter- nal resistance of the tube. It is to be expected that as time goes on. this value will change and the apparatus will need appropriate adjustment. Nothing particular can be said as far as the thyratron is concerned. It can be pointed out only that as for any mercury filled tube. its operation is subject to changes depending on the temperature of the mercury. Ihis has not a very great importance on the stability of the apparatus since the firing time has to be con- trolled entirely by the blocking oscillator and not by the thyratron. BIBLIOGRAPHY U. 8. Navy Department Radar Electronic lundamentals (19W) M.I.!. Radar School Staff Irinciples 3; Radar (19146) McCray Hill Book Company, New York Reich. H. J. Theogz and; Applications 5 Electron Tubes (19%) McGrav Hill Book Company, New York Iortrat B. Lecons 9.3 Badioelectricite (19%) Librairie Masson. Paris France Bruhat, G. Genre 5}; Esigue generale Electricite (191th) Librairie Masson, Paris J'rance Boeard, I. Lg; oscillations (19145) Librairie Nasson. Paris Irance HICHIGQN STATE UNIV. LIBRQRIES I|II|IIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIIII|I|I3IIIII|| 3129301774973