Патент USA US2406804код для вставки
Sept- 3, 1946\ . P. K. CHATTERJEA ETAL NEGATIVE RESISTANCE DEVICE FOR GENERATING OSCILLATIONS OR REDUCING DAMPING Filed Nov. 6, ‘1943 VOLTAGE CURRENT, 2,406,804 _ Patented Sept. 3, 1946 2,406,804 UNITED STATES PATENT OFFICE 2,406,804 N EGATIV E1 RESISTANCE DEVICE. FDR' GEN; ERATING OSCIL'IJATIONS" OR‘ REDUCING DAMPING Prafulla Kuniar Chatterjea and Charles Thomas Scully, London, England, assignors, bymesnc assignments, to International Standard Electric Corporation; New York, N. Y.', a corporation oi‘ Delaware Application November 6, 1943, Serial ‘No. 509,188 in Great ‘Britain .ianuarygS, 1943.. 1 Claim: (Cl. 250—36) 1.; 2 The "present invention relates. to. clectricres onan'ti circuits ‘particularly those used in oscil lation generators and employs (the special. prop— ei'tiesv of thextherinally sensitive'resistance ele thereforemay. be used‘to generatexoscillations in‘ a‘ resonant: circuit in; a: particularly simple way; By‘ suitablexacljustment of the'constants' of the. circuit; oscillations ' may just :be' prevented. from‘ occurring;- and: in"v that casea resonant circuit, ments known as thermistors. Thermistors are. thermosensitive resistance ele_ which may have a very low resonance frequency mentshavinga temperature coefficient of resist ancevvhich may be either positive or negative-and and a very highvalueof Q", .may be easily "ob‘_ tained foruse in?lter and. other like circuits. which is moreover many times the corresponding According. toone aspect'of the invention; there coef?cient ‘for a pure metal such as copper; This fore, theretisnprovided 'an electric resonant cir.-' cuit comprising an'inductance, a thermistor hav ing .a: negative temperature coefficient of ‘resist; ance, and‘ a source of direct current; coupled; propertyrenders thermistors particularly suitable for a variety of special applications in electric circuits. together in such a manner ‘that the. ratio of "re-1 Various different- materials are available for the resistance element of a thermistor, these vari 15 actanceito resistance of the inductance. isiefliec'~ tively raised ‘ to a; predetermined . value. ous materials having different ‘properties in other Accordingto another aspect; thezinvention'pro respects; as: one example, a-resistance material vides anelectric: resonant circuit comprising- an' having a high negative temperature coef?cient of inductance at least part of which is; connected" resistance comprises a» mixture of manganese in series with the resistanceielement of fav thermis oxide,land nickel oxide'w-ith or'without'the-addi tor‘ having a negative temperature coei?cient‘ of tion of certain‘ othermetallic oxides, the mix ture being suitably heat treated. ' Thermistors have been employedinxtwo dif resistance, to'avsource of direct current, theth'ere mistorvcircuit resistancebeing adjustedso that the voltage-current characteristic curve‘ of; the ferent forms: (a) - known‘asral-directlyrheated thermistor andfcomprisingr a resistance element 25 thermistor circuit'h'as a portion; whose slope is slightly’- positive,. and. vso "that the current through of the thermally sensitive resistance material ‘pro the-resistance element is represented-byapoint vided with'suitable lead-out conductors or ter on the said portion of slightly positive slope; minals, and (b) known as'an'iindir'ectly» heated Accordingto the invention, also; the thermis thermistor comprising 'tlie'ele'ment. (a) provided in addition with a heating’. coil electrically-‘ma 30 toreircuit resistance‘in either of the abovemem. tioned aspects. may be alternatively adjusted =50 sulatedi from the element. Al- directly 1 heated that oscillations take place in thereson-antcir thermistor is primarily intended to b'elcontrolled cuit. . by the currentwhich flows through it and which The invention awill be described with reference variesthe temperature and also the resistance to the accompanying drawing in which»: accordingly. Such a. thermistor willll'also b'e af Fig; 1 shows'an example‘of one circuit-accord fected bythe temperature of its surroundings-and ingv to" the invention; and ‘ maytherefore be used for‘ thermostatic control Fig; 2fshows ' characteristic curves‘ used to -ex-~ and‘likekpurposes-With or Without direct'h'eating» plain the operation'of'Fig. 1. by the current ?owing through it. An indirectly It will be understood that any'resistances ‘other: heated thermistor is chie?y designed to be heated 40 than thermistors‘emp-loyed in'this inventionare by- a controlling current which flowsthrough the of the ordinary kind in which the resistance value heating coil and'which will usually, but not nec is substantially:-independent of the current. essarily, be different from the current which Fig. 1 shows an example of a circuit accord flows through the resistance element, but this ing to the invention. An indirectly heated ther type of thermistor may also be subjected to either mistor T having a negative temperature coeffi or both of the types of control applicable to a cient of resistance has its resistance element directly heated thermistor. R connected in series with part of an inductance More detailed information on the properties of L and a tapped battery or other direct current thermistors will be found in an article by G. L. Pearson in the Bell Laboratories’ Record Dec. 50 source E‘. The heating coil 1' of the thermistor is connected to the battery in series with an ad 1940, page 106. justable resistance R1. A parallel resonant cir In the present invention, thermistors having a cuit is produced by connecting a condenser C negative temperature coeiiicient of resistance are employed, since under appropriate conditions across the inductance L. In Fig. 2 are shown characteristic curves for the they may behave like negative resistances and 55 2,406,804 3 circuit of Fig. 1. The abscissae represent the cur rents and the ordinates the corresponding volt ages. Curve A shows the curve for the thermistor T alone, with no current in the heating coil. As the current through the resistance element R is in creased, the voltage across R ?rst increases to a maximum and then decreases continuously. The part of the curve beyond the maximum has a negative slope, and this means that the effective resistance to current changes is negative. The straight line B represents the characteris tic for the resistance of that part of the induct ance L which is in series with the thermistor (to gether with any other resistance there may be in the circuit) and this resistance is assumed to be substantially constant. Curve C has been ob— tained by adding the ordinates of curves A and B, and represents the resistance characteristic 4 it does not contain any valves which would re— quire a high tension or cathode heating source. It would be useful, for example, as a low fre quency generator; as a vibrator for power packs, or to generate ringing frequencies for telephone circuits. Referring again to Fig. 2, if the resistance con nected in series with the resistance element R be increased, the slope of the curve B will be also increased and the horizontal part of the curve C will move to the left until it reaches the volt age maXimum of the curve. At, or a little after, this stage, the curve C will be found to have no horizontal portion, and no portion of negative slope, but there will be a short region in the neighbourhood of the maximum of the curve where the slope is only very slightly positive. Under these conditions oscillations will not oc~ our, but the ratio Q of reactance to resistance of of the whole of the circuit. It will be seen that curve C is horizontal in the neighbourhood of the point P signifying that the effective resistance to changing currents is zero. According to the inductance L may effectively be very high, and can be given any desired value by suitably termined substantially by L and C. The effect of passing a current through the cult at low frequencies, requiring very bulky coils or complicated amplifying arrangements by heating coil 1 will be generally to lower the curves A and C and to render the voltage maximum less sharp. Curve D shows the manner in which the curve A would thus be changed. This provides a convenient means of adjusting the character istic of the thermistor to produce the desired os cillation condition. The operation of the circuit known methods. adjusting the circuit. In this way a resonant circuit L, C tuned to a very low frequency, and known principles, the circuit will oscillate in the having a very high value of Q, is obtained in a neighbourhood of the point P at a frequency de- 7,- very simple way; this is well known to be dini may also be controlled by including a suitable re~ - It may be added that another method of ob taining the desired slightly positive slope is to adjust the resistance R1 in Fig. 1 instead of ad justing the resistance in series with R. By in creasing the current through the heating coil 1 the horizontal portion of the curve C will also move to the left until it disappears in the neigh sistance (not shown) in series with the thermis bourhood of the maximum of the curve. It is tor element R. This will change the slope of the further to be noted that in Fig. 1, the current for line B in Fig. 2. the heating coil r could, if desired, be obtained The oscillation output may be taken from the from a direct or alternating current source (not tuned circuit L, C in any suitable way (not 40 shown) entirely separate from the direct current shown). Although adjustable connections to source E. the battery and to the inductance L are indicated What is claimed is: for convenience, these could of course be ?xed; Electrical circuit including, connected in se and if adjustment of the characteristics of the ries, an indirectly heated, negative characteris thermistor are not required, one of the directly tic thermistor, a source of direct current, and at heated type could be used, the resistance R1 and least part of an inductance, also including a ca its connections being omitted. pacity shunting said inductance and forming The tuned circuit could furthermore be cou therewith a resonant circuit, said series connect pled to the thermistor circuit by means of a ed circuit also including a variable resistance separate winding (not shown) coupled to the in 60 connected in series with the heater of said ther ductance L, and connected in series with the mistor, whereby the characteristic voltage-cur thermistor and source E, and various other mod rent curve of said thermistor may be altered in i?cations will occur to those skilled in the art. shape and position, so that a given current ?ow It should be added that owing to the fact that therethrough may be made to lie at a predeter the response of the thermistor to changes in the 55 mined point of said curve, said point being lo current is not instantaneous, the frequencies to cated at a portion of said curve having suflicient which the circuit is applicable will generally be negative slope to cause said resonant circuit to low. Thermistors having very rapid response oscillate. are however known, and frequencies of several hundred periods per second may be possible. PRAFULLA KUMAR CHATTERJE'A. 60 ‘The circuit of Fig. 1 is particularly simple since CHARLES THOMAS SCULLY.