US2230297A - System of translating the minute variation of inductance or capacity into the variation of electric current or voltage - Google Patents

Description

Feb. 4, 194i. H. ,NOUE 230,297

SYSTEM 0F TRANSLATING THB MINUTE VARIATION OF INDUCTANCE OR CAPACITY INTO THE IVARIATION OF ELECTRC` CURRENT OR VOLTAGE v' Filed sept. 26, 1959 ATTORNEYS.

Patented ret. 4, 1941A. Y i l 2,f30-,29I1

UlAilTF-D STATEsP-ATENT OFI-ics 'ITY INTO THE VARIATION 0F ELECTRIC CURRENT B. VOLTAGE mmm nume, shim@ ranmasuginami-x,

y Tokyo, Japan f Application September 26., 1939, Serial No. 296572 In Japan September 30, 1938 This invention relates to a system of translat- I positive half cycle of the given high frequency ing the minufte variation of inductance or capacoscillation. The mean value of the plate current ity into the variation of electric current or voltis determined by the control grid voltage-both age. which consists in impressing high frequency amplitude and the relative phase relation to the voltage upon the screen grids of tetrode or pen. screen grid voltage phase-under the constant s tode valves trompa separate high frequency oscil- 'plate voltage and the constant screen grid exlator, and on the other hand forming a tuning citation. The control grid I is connected to the circuit vincluding inductance or capacity. under tuning circuit 1, which is composed of 'condenser measurement; connecting said circuit to the con- I under measurement, condenser I0, and coil 9. m trol grid of the concerned for completing the Said tuning circuit, approximately tuned to the lo grid circuit; feeding the voltage vof the' oscillator oscillator frequency,v is' supplied high frequency to said tuning circuit through the inter-electrode voltage from the oscillator through the inter' capacity between the electrodes between the'- electrode capacity between control grid I 4and above mentioned'two grids or by using also the screengrld 5. Y Grid leak resistance li and byouter connecting circuit; inserting an automatic pass condenser I2 are provided as an automaticu 1 bias device consisting of grid leak resistance and bias device using grid current. Thus, the potenby-pass condenser into the cathode return oftial of the control grid 6 is given as the superthe above grid circuit varying the plate current position of both the\high frequency -drop voltage of said valve by utilizing the quick variation of across the tuning circuit 1 and D. C. bias voltage the high frequency voltage phase of the tuning across resistance II. e g() circuit and the variation of the control grid volt- Next, to explain the operation of the above sysage when the minute change of the test capacity tem, Figure i.` shows a relation between the voltor inductance occurs, and'thus translating the ages Jof the screen grid `and 'the control grid. minute variation of capacity or inductance into Figure 3 illustrates that the phase of the termithe corresponding change of voltage or current. nal Ivoltage of the tuning circuit varies at the 25 'Ihe object of the presentvinvention is to provide detuning of said circuit. If thepotentials of the a system for improving thesensibility, accuracy grids land I are then given the same phase by and stability of such a circuit system as utilizes adjusting th`e capacity Il of rthe tuning circuit phase shifting due to the variation of the res- I in Figure 1, the plate current of the vacuum 30 onant frequency tuning circuit, especially for valve l' will show the maximum value.- That is, 30`

easily obtaining a desirable long maintenance off when the -potential ofthe control grid has the calibration hitherto considered diicult in this Esame phase as the screen grid potential as kind of circuit, by improving and simplifying the illustrated at (2B1) the `indication of an amknown system a great deal, and alsoby using the meter Il shown inFigure l will show the maxivariation of the control grid voltage due to the mumvalue. I .35

. tuning frequency. Y Next,if the value of the test capacity B changes i Referring to the appended drawing, f by AC from the above condition, a difference in Figure 1 is a diagram of an electrical connecthe phase of voltage between the grids l and G tion showing an example of .the manner of carwill become 0, and the plate current gradually 40 rying out tlie present system into practice; decreases` as 0 increases, according to lthe value o Figure 21s a graphic explanation of a relation of AC. Figure 2 illustrates this performance; an 'between two control grids in the phase of elecarea having hatching lines indicates the part tric potential; 'f i where the plate current cannot flow and accord- Figure 3 a diagram showing :the phase varia-f ingly the greater that part is, the smaller the- 5' tion due to capacity variation; w plate current will be. That is to'say,. the value 45 l Figure 4 is a diagram showing the operation of of AC causes the great or small variation of 0 and' this system. theJ great or small variation of 0 produces the Iny Figure U1, the output of an oscillator i is corresponding degree of the plate current. In transmitted into a coupling coil 2, thus causing other words, the degree of the variation -of the the-fall of thevoltage/toboth terminals of a test capacity may be measured by that ofthe 50 tuning circuit comprisingacoillf and condenser plate current. A resistance I4 translatesvthe l, and feeding said voltage to a suitable vacuum plate lcurrent variation into voltage variationi if valve, for instance, to the screen grid electrode, necessary. It is also the case with the variation 5 of a pentode 4. The plate current of said valve of the inductance l.

', 55' isl able to iiow only when the screen gridl is at The above explanation shows briey the ope- 55 ation and idea of the present system with ree gard to a phase relation, but inpractice this system operates in a somewhat more complicated form. That islto say, so long as the anode voltage is not extremely great, the plate current begins to ow from the point and increases with the increment of the test ca-` pacity C or test inductance L.v In the above formula, w represents oscillator angular frequency; L,'the inductance of the coil 9 in Figure 1; C, the sum of the capacity of the condensers 8 land I0,.and Co, the coupling capacity between the grids 5 and -6. For the purpose of increasing C, the outer capacity may be added in parallel be" tween the grids 5 and 6. Q represents at the'tuning circuit 1.- 'R is the loss resistance in the-above circuit 1. Y

The point shown Vby'the above formula, the' starting point of the plate current, indicates the the coupling capacity Co.y The high frequency,

tuning point of the whole grid circuitincluding voltage of the grid 6 shows the maximum value at that point and the phase difference between the grids 5 and 6 is 90 .Figure 4- illustrates a re' lation between the variations of high frequency control grid voltage Egfvand plate current Ip.

As C or L increases, or in other words, the phase dierence between the voltages of the grids 5 and 6 is-reduced, the plate current increases and at the same time the high frequency voltage Eg appliedto the grid 6 is reduced quickly.

It must be noted here that the present system utilizes an automaticbias device consisting of a r'esistance I I and capacity l 2 as an automatic bias for the grid 6'. It is the well-known fact that in the bias system employing grid current, the plate current increases with the reductionof the high frequency voltage impressed on the control grid. In this system, the high frequency voltage pressed K vupon the grid 6 is greatest when the plate current known systems.

begins to flow. With reduction of the phase difference from this point, the voltage of the grid 6 is simultaneously reduced, and by their co-operation the plate current is considerably increased. Thus, since this system uses the phase variation and voltage variation together instead of being the mere combination of a tuning circuit and phase meter, it is able to operate with very high sensibility. l

Next, let me explain what characteristic featurev this invention has as compared with the The systems for measuring minute variation of capacity or inductance have been studied for'more than ten years, because I they are very useful for measuring mechanical displacement through a medium of capacityor phant has succeeded in measuring and recording inductance, whose value is varied by mechanical displacement under measurement.

One ofy the most effective systems is such a one as to utilize the rapid phase change of the high frequency voltage across thel resonant circuit under shifting of its tuning frequency. A I y By utilizing such av system ingeniously, Olithe variation of the pressure of uidr' AHe has also published its application to other eldsin "The Journal of Scientific Instruments, pages 386-388,'01 Dec.. 1932.

My system too utilizes the phase shifting phenomenon of the tuning circuit, but unlike the known circuit, it has such remarkable features as utilize voltage variation also.

The novel feature of the present invention con-v sists in making a vacuum valve phaseand volt meter by a new circuit system, combining-itin- 'v geniously with the tuning circuit including a test article by a new process, and utilizing `both the ,phase difference and voltage variation by using an automatic bias,v andP thus translating minute capacity or minute inductance variation into large current or voltage variation.

'Ifhe following points form the main basis which utilizing the capacity between the inner grids ofthe vacuum valve, thus taking the terminal volt-v age of the tuning circuit comprising the coil 2 and condenser 3 in Figure 1J at the standard I vector, and putting the phase variation of the screen grid voltage due to the undesirable Variation of the constants of said circuit out ofthe question. f

(3) The screen grid is notprovided with any other energy supply source than the output of the high frequency oscillator, and itis so devised that absolutely no self-oscillation occurs, even if tuning circuits are provided simultaneously at the two control electrodes of one vacuum valve. y

(4) If the detuning of the tuning circuit, comprising the test article in Figure 1 reaches ,a cer- .tain limit, the plate current becomes zero, and if it is turned to the opposite direction, the plate current reaches a saturation value which may be easily brought into agreement with the given value of the first calibration by varying the degree of the coupling of the output of the oscillator l, or by adjusting the tuning circuit 3 shown in the above gure. In this way, the long maintenance of calibration as is dicult in this kind of circuit 'may be obtained easily by simply keeping `constant the value of the ,inductance 9. y y

In accordance with the abovementioned 'fea tures of the present invention, it is possible to overcome ,the manyftechical diiiiculties encoun-v tered in manufacturing the system for translat` ing the variation of capacity or inductance into that of current or voltage and to increase the stability, accuracy' and sensibility and also simplify the construction, cffthe system. .l

According to my experiment, il?` in `this system a valve (1.1257) is,used as a detecting `vacuum f valve and a valve (6L6) fused as a crystal controlled oscillator and oscillation frequency 3500 kc. adopted,N the plate voltage supply is 250` volts, and the capacity oi.' the tuning circuit 1 is about micromicrofarads, then the variationv of the plate current. when unloadedv is 10.5 microamperes for the va ation $4.000' micromicrofarad of the capacity in t e tuning-circuit. Also, if in the same condition a resistance of 500,900 ohms is inserted intoA plate circuit, the voltage variation across it is 2.75 volts per M000 micromicrofarad and the range of lthe voltage variationA is 0-220 volts. i

A invention, meters or relays can be operated by utilizing such minute variation of the capacity asmooo micromicrofarad. A concrete circuit capable of detecting such minute capacity variation so easily has never been expected. Indeed, the present circuit contributes a great deal to the improvement of the electrical and mechanical engineering arts.

Having now fully described my invention, I claim:

System .of translating the minute variation of inductance or capacity into the corresponding change of current or voltage, which comprises a valve which is at least a tetrode valve and may be pentode valve, a separate high frequency oscillator for. impreing 'high frequency voltage upon the screen grid of said valve. a separate tuning circuit including inductance or capacity 20. under measurement, said tuning circuit being connected to the control grid of the valve for completing a control grid circuit and supplied with the high frequency voltage through the interelectrode capacity between screen gridand control grid or outer feeding circuit, and an automatic bias device consisting of grid leak resistance and by-pass condenser, inserted in the cath-A ode return of the control grid circuit, producing control grid voltage variation, and quick variation of the phase difference between control grid and screen grid voltage, which are due to `the variation of the resonant frequency of said tuning circuit caused by the change of inductance or capacityunder measurementfso as to utilize both variations in order to produce the change of the plate current of said valve and' translate the minute variation of capacity or inductance into the corresponding change of voltage or current.

HITOSHI INOUE.

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