US2878351A - Heated thermistor - Google Patents

Description

March 17, 1959 w. R. POLYE 2,878,351

HEATED THERMISTOR Filed July 2. 1953 FIG. 1

INVENTOR. W/LL/AM R POU/E HEATED THERMISTOR William Ronald Polye, River Edge, N. I., assignor tov Bendix Aviation Corporation, Teterboro, N. J., a corporation of Delaware Application July 2, 1953, Serial No. 365,605

3 Claims. (Cl. 201-63) The general purpose of the invention is to provide` a heated thermistor which will be free from appreciable inductive effect while retaining the useful characteristics of the wire-wound type.

A specific object is to provide a heating element that can be effectively applied to and operated with a thermistor element of standard type without including a wire winding.

Heated thermistors may be constructed to provide a calculated time delay between the time when the heating element is energized and the time when its heat has produced a predetermined change in the resistance of the thermistor element. This is in general accomplished by the use of insulation having an appropriate heat coefficient and thickness between the two elements. A further purpose of the invention is to provide a heated thermistor of this type that will be practical in construction and reliable in use without employing wire windings.

Other objects are toproyide a non-inductive thermistor that is simple andcompact, that may use standard types of thermistor elements, and one which may be of suitable proportions for enclosure in a protective tube or other casing.

These and other objects and advantages of the invention will appear more fully from consideration of the following detailed description, in conjunction with the accompanying drawing, in which one embodiment of the invention is illustrated. It is to be expressly understood, however, that the drawing is for the purposes of illustration and description, and is not to be construed as defining the limits of the invention.

In the drawing:

Fig. 1 is a longitudinal central section through a protective tube enclosing two heated thermistors embodying the invention, one thermistor being shown in longitudinal central section, and

Fig. 2 is a diagram of a circuit in which the arrangement shown in Fig. l may be used.

Referring first to the construction illustrated in Fig. 1, the heated thermistor comprises a ceramic thermistor 11 of the standard rod type, provided adjacent its ends with wire leads 12. Suitable insulation is applied to the thermistor rod 11, the form illustrated employing a layer of ceramic glaze 13, which may envelop the ends of thermistor 11 and of leads 12, as shown, though this is not essential.

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A suitable heating arrangement is applied to the insulating layer 13, and advantageously is in the form of sheet material extending around said layer. In the form illustrated, a layer of carbon, and specifically of graphite 14, is employed, which may be applied to the glaze 13 by spraying.

Suitable leads are connected to the heating element 14 adjacent its ends. For this purpose strip metal leads 15 may be wrapped around the insulating layer 13 in electrical connection with end portions of the heating layer 14. An eflicient arrangement of this type is shown,`

. including annular metallic elements or layers in the form of deposits 16 extending around the insulating layer 13 and advantageously fired into the glaze. The layer of heating material 14'overlies the inner end portions of deposits 16 in conducting Contact therewith, and leads 15 extend around said deposits in conducting engagement with such deposits. a

The heated thermistor arrangement described 1s designed for efficient manufacture by standard processes.

The insulating layer 13 is advantageously of a type thaty 'may be readily applied by heat, and advantageously consists of a material formed into an adhering layer by heating and cooling, generally termed a ceramic glaze, and having known insulating properties. The connecting element 16 is formed of any suitable metal, metallic compound, carbon or other conducting material, and may be applied to or incorporated in the outer surface of the insulating coating 13 in sheet or comminuted form before firing, the latter operation serving to make the conductor 16 an integral part of insulation 13. The heating element 14 advantageously comprises finely divided carbon, such as graphite in a suitable volatile vehicle, and may be applied to the insulation 13 by spraying, though other methods of applying a suitable heating material, such as painting or sputtering, may be employed when appropriate for the material used.

The described arrangement may be extremely compact and is adapted to be mounted within a suitable casing of relatively small size. A mounting of this type is illustrated, showing two heated thermistors mounted in an evacuated glass tube 17. In this arrangement the upper leads 12 connected to the thermistors 11 are iixed to a supporting and conducting` rod 18, while the lower leads 12 are connected to lead-out wires 19. The heating element leads 15 are connected to lead-out wires 20. Rod 18and wires 19, 20 extend through the bottom of tube 17, and may be connected to a standard seven-prong base (not shown) in the usual manner.

While the parts illustrated in Fig. 1 have been shown in transverse alignment for simplicity of illustration and description, it will be evident that the construction of the units 10 is particularly adapted to facilitate their mounting in very close parallel proximity, so that a casing containing two or more heated thermistors 10 may he very small in size without sacrificing etiiciency. The

absence of inductive elements moreover prevents any possibility of thermistors.

The arrangement shown in Fig. 1 is particularly adapted for use in bridge circuits such as that illustrated in Fig. 2, in which the portion incorporated in the Fig. 1 structure is indicated within dotted lines. To complete the circuit, it is necessary only to connect the additional bridge resistors 21 to the leads 19, lead 18 to one of the inner bridge terminals 22 and leads 19 to the outer bridge terminals 23.

The leads 20 through which the heating elements 14 are energized are connected to suitable sources, which may be provided by any ofthe numerous control or other circuits which employ this arrangement. The bridge circuits will of course be connected across terminals 22, 23, in the usual way. The arrangement for enerinductive coupling between different thev contacts-ofwhich are connected to terminalss24. By;`

operating switch 26;, either of the: heatingaelements 1. 14 may be energized, witha resultingV change in the resistance:`

of the-associated thermistor 11, therebyfunbalancing:the-1.

bridge and causing current to 110W across the bridge-ins the selected direction;

The Word thermistor as used herein is'intended to.v indicate a resistanceyelement.whose resistance' isvaried;

to a substantial anduseful extent :whensits temperature-:ist

varied ywithin practical limits;

Although t one embodiment ,oft ther invention 4hast beenr,

illustrated and ,described in detail,v itk isato be :expressly-v understoody thatY the invention is." not 'limited'. theretoa. Various `changes can be made in the-design; arrangement;y

construction and .materials of v the parts..v without departs;l

ingqfromthe spiritl and scopeofzthe nventionfastthei.

same will now be understood by those skilledainLthetartz..

I claim:

1.,A. heated. thermistor-r comprising:- aee rodfshapecl..

ceramic thermistor, a-layer ofzceramic insulatonsurroundiingthe thermistor; and a layerof lgraphite surrounding then insulation layer.'v

2.A A heated thermistor unit comprisingitwoz axially;A

oiset non-inductive heated thermistors: eachA including am Y mengsel,

elongatednoneinductive.thermistor, zaesheet of: insulatiom.

surrounding the thermistor and a non-inductive heating element on the insulation; and a support for the ther mistors arranged to maintain said thermistors in axially otset parallel proximity.

3. A heated thermistor. unit comprising two axially offset non-inductive heated'thermistors, each including an elongated non-inductive thermistor, leadsadjacent to the ends of the thermistor, insulation on, the 1 thermistor, a non-inductive heating ielement extending;*longitudinally along the insulation, and leads connected ',to said element adjacent to the ends of the thermistor; and a support for said iheated thermistors.,incldingsafmembertengaging a lead from each heatedthermistor,A `arranged to maintain said thermistors in parallel' axially loffsetproximity References Cited in the ile of this patent UNITED? STATESPATENTS.'

1,157,916' Wentworth Oct; 26,1,1915' 126333511' Schneider Apr; 16;"19182 1,847,653 Ionesetal." Man 1,] 19321 2,178,548` Black et. al. -..,Nv.'x7',' 1939`Y 2;'3'66f614f' Hnsell Iam 2;.1945.. 22434560 Gnter` Jn. 13,1948y FOREIGN PATENTS 780160? France"V Jan: 24,119.35.'v 645,007..y Germany* May20, 1937

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