Variable Resistance Resistor Assembly

Abstract

A variable resistance resistor assembly comprises as its central component a resistance element in sheet form, which can be an ohmic resistor, a thermistor having a positive or negative temperature coefficient of resistivity, a varistor, or the like. One side of the resistance element sheet is provided with a pair of terminal electrodes, between which the resistance of the resistor assembly is varied. On the opposite side of the resistance element sheet there is provided a plurality of resistance variance electrodes, which can be shorted out to vary the resistance of the resistor assembly.

Description

BACKGROUND OF THE INVENTION

This invention relates to variable resistance resistor assemblies. As electronic equipment becomes more and more complicated, an increasingly wide variety of resistance elements is needed. These include the traditional or ohmic resistors, as well as such elements as thermistors which change their resistance in response to a change in temperature, either including resistance with increasing temperature, in which case the thermistor is said to be a positive temperature coefficient or PTC thermistor; or decreasing their resistance with increasing temperature, in which case the resistance element is said to be a negative temperature coefficient or NTC thermistor. Another variety of resistor is the varistor, which changes its resistance in response to a change in voltage. In the varistor, the amount of current which flows through the resistance element is nonlinear with respect to the applied voltage.

All of these types of resistance elements are required in various magnitudes, in order to produce electronic equipment. Furthermore, the operation of some electrical equipment, such as the start-up of a large electric motor, requires the use of variable components. When a large electric motor is initially started, it cannot tolerate a large current passing through its armature, lest the armature becomes burned out through the generation of excessive heat. After the motor is running, however, successively larger amounts of current can be tolerated, and are needed to bring the motor up to full speed. It is therefore customary in starting such motors to utilize a decreasing resistance in series with the armatures so that while the amount of current which flows through the armature initially is small, after speed is built up to a degree, the resistance can be removed in steps and the speed of the motor can therefore be increased as the amount of current passing through the armature increase. The opposite is true of the field windings, which not only can tolerate but require large currents initially to start the motor (to overcome inertia and friction by using a larger starting torque). A PTC thermistor can be connected in series with the field windings, so that an initial large rush of current is produced. After the motor is turning, the current is automatically reduced in the field windings because the resistance in the PTC thermistor, in series with the field windings, has increased.

An application for NTC thermistors is the extension of life of filaments used in electric lamps. An NTC thermistor is connected in series with the lamp filament so that the initially high resistance of the NTC thermistor prevents an inrush of current through the cold filament which is relatively low is resistance. As the temperature of the lamp filament rises, so does its resistance; but the resistance of the NTC thermistor drops. The sum of the resistances of the filament and the NTC thermistor is therefore always sufficient to prevent too much current from passing through the filament; but the NTC thermistor has sufficiently low resistance after warm up that it does not interfere with the operation of the lamp.

Another application of the NTC thermistor is to provide temperature compensation for an ordinary resistor which has a low, but positive, temperature coefficient of resistivity. By connecting these elements together, it is possible to provide a combination which has a more nearly ohmic (linear) total resistance. For these and other purposes, there is a need for resistor assemblies in which the resistance can be easily and quickly varied, either temporarily or permanently.

SUMMARY OF THE INVENTION

These and other objects are provided with a variable resistance resistor assembly, comprising in combination a resistance element in sheet form, i.e., a resistance element sheet; a pair of terminal electrodes on one side of the resistance element sheet; and a plurality of resistance variance electrodes on the other side of the resistance element sheet. The resistance variance electrodes can be shorted out, either temporarily or permanently, to vary the resistance of the resistor assembly.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an end view of a variable resistance resistor assembly in accordance with the present invention.

FIG. 2 is a plan view of the variable resistance resistor assembly of FIG. 1.

FIG. 3 is a plan view of a variable resistance resistor assembly similar to that of FIGS. 1 and 2, but comprising in addition additional circuitry to increase the versatility of the resistor assembly.

DETAILED DESCRIPTION

Referring again to the drawings, FIGS. 1 and 2 illustrate a first embodiment of the present invention. Resistance element in sheet form (i.e., resistance element sheet) 11 is the central component of the variable resistance resistor assembly. Resistance element sheet 11 is provided with a pair of terminal electrodes 12 and 13, between which the resistance of the variable resistance resistor assembly is varied. Terminal electrodes 12 and 13 are connected to leads 14 and 15, respectively. On the opposite side of the resistance element sheet 11, there is provided a plurality of resistance variance electrodes 16-20. While the electrodes 16-20, as illustrated, are each parallel to terminal electrodes 12 and 13, this is only a preferred embodiment which gives greater uniformity, since electrodes 16-20 can be arranged in other configurations as well. For example, electrodes 16-20 can be replaced with small spot electrodes on the side of the resistance element sheet 11 opposite terminal electrodes 12 and 13.

Large numbers of variable resistance resistor assemblies in this form can be stored and a variety of resistances can be produced from the single type of resistor assembly at a later time as they are needed. For example, if the resistance of resistance element sheet 11 between electrodes 12 and 13 is ordinarily about 1,500 ohms and between electrodes 12 and 16 about 100 ohms, then the resistance between electrodes 12 and 17 could be expected to be about 400 ohms, between electrodes 17 and 18 about 350 ohms, between electrodes 18 and 19 about 350 ohms, and between electrodes 19 and 13 about 400 ohms. By placing a permanent connection between electrodes 16 and 20, a 200 ohm resistor can be easily prepared. By placing a permanent connection between electrodes 16 and 17, and a second permanent connection between leads 18 and 20, a permanent resistance of about 550 ohms can be quickly prepared. The resistor assembly can of course be used with no permanent leads between any of electrodes 16-20, so that the full resistance of 1,500 ohms is utilized.

Alternatively, and as illustrated in FIG. 1, the same variable resistance resistor assembly can be provided with a plurality of switch contacts 21-25, electrically connected to electrodes 16-20, respectively. Switch 26 can then bridge the gap between switch contact 21 and one of switch contacts, 22, 23, 24, or 25, so that the resistance of the resistor assembly can be varied at will. In addition, a dead switch contact 27 can be provided, so that the full resistance of the resistor assembly can be utilized. If desired, the movement of switch 26 can be controlled electrically, remotely, and even varied regularly on a periodic basis, if desired.

Referring now to FIG. 3, there is illustrated a further embodiment of the present invention, which utilizes supplemental circuitry to provide a higher degree of flexibility of the variable resistance resistor assembly. Shunt resistance elements 31-34 are each provided with two leads, one of which is permanently electrically connected to one terminal electrode 13 on the first side of the resistance element sheet 11. The resistor assembly can be stored in this condition for later utilization, and the remaining lead of one or more of resistors 31-34 can be connected to the opposing terminal 12 an the first side of resistance element sheet 11, if desired. Alternatively, the second lead from each shunt resistance element 31-34 can be connected to switch contacts 35-38, respectivly. An additional switch contact 39 can be connected to terminal electrode 12 on resistance element sheet 11. Switch 40 can then be utilized to provide a supplementary path for electrons to flow between terminal electrode 12 and terminal electrode 13, so that one of shunt resistance elements 31--34 is connected in parallel with the effective resistance of resistance element sheet 11. Dead switch contact 41 can be utilized in the event that it is desired to provide no such alternate electron path. Each of switch contacts 35-39 and 41 are, of course, insulated from resistance element sheet 11, except as indicated.

Switches 26 and 40 can be moved independently, to provide a wide variety of different net resistances between terminal electrode 12 and terminal electrode 13, or these two switches 26 and 40 can be provided with a common switching mechanism so that switches 26 and 40 are moved at the same time. This could particularly be the case if the resistance materials of resistance element sheet 11 and shunt resistance element 31-34 are of a different nature. For example, resistance element sheet 11 could be a thermistor material, and shunt resistance elements 31-34 could be traditional ohmic resistors. Assuming shunt resistance elements 31-34 have successively smaller resistances, switches 26 and 40 could then be arranged to move together from switch contacts 22 and 35, respectively, to switch contacts 23 and 36, respectively, to switch contacts 24 and 37, respectively, and finally to switch contacts 25 and 38, respectively, so that the same balance between thermistor resistance and ohmic resistance is maintained, even though the total resistance is successively made less and less as each progressive switch contact is made.

The variable resistance resistor assemblies of the present invention are of great utility in building up an inventory of similar electronic components which can be easily converted to a wide variety of different electronic components, which reduces the number of separate individual inventory items which must be maintained in order to provide a relatively large variety of resistance elements. Alternatively, by use of switches such as switches 26 and 40, the resistance of a given resistor assembly can be varied periodically for such applications as attenuators to vary power output.

Claims

I claim:

1. A variable resistance resistor assembly, comprising

1. a resistance element in sheet form;

2. a pair of terminal electrodes on a first side of said resistance element sheet; and

3. a plurality of resistance variance electrodes on the opposite side of said resistance element sheet.

2. A variable resistance resistor assembly according to claim 1, comprising in addition means for closing electrical contact between a pair of said resistance variance electrodes.

3. A variable resistance resistor assembly according to claim 2, wherein said pair of resistance variance electrodes is permanently electrically connected.

4. A variable resistance resistor assembly according to claim 2, wherein said pair of resistance variance electrodes is temporarily electrically connected.

5. A variable resistance resistor assembly according to claim 1, comprising in addition at least one shunt resistance element, one lead of which is permanently electrically connected to one terminal electrode on the first side of said resistance element sheet.

6. A variable resistance resistor assembly according to claim 5, comprising in addition means for closing electrical contact between a second lead of said shunt resistance element and the second terminal electrode on the first side of said resistance element sheet.

7. A variable resistance resistor assembly according to claim 6, wherein said second shunt resistor lead is permanently electrically connected to said second terminal electrode.

8. A variable resistance resistor assembly according to claim 6, wherein said second shunt resistance lead is temporarily electrically connected to said second terminal electrode.