GB2032191A - Improvements in Electrical Resistors - Google Patents

Improvements in Electrical Resistors Download PDF

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Publication number
GB2032191A
GB2032191A GB7839025A GB7839025A GB2032191A GB 2032191 A GB2032191 A GB 2032191A GB 7839025 A GB7839025 A GB 7839025A GB 7839025 A GB7839025 A GB 7839025A GB 2032191 A GB2032191 A GB 2032191A
Authority
GB
United Kingdom
Prior art keywords
resistor
envelope
band
terminals
electrical
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
GB7839025A
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Welwyn Electric Ltd
Original Assignee
Welwyn Electric Ltd
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Welwyn Electric Ltd filed Critical Welwyn Electric Ltd
Priority to GB7839025A priority Critical patent/GB2032191A/en
Publication of GB2032191A publication Critical patent/GB2032191A/en
Withdrawn legal-status Critical Current

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Classifications

    • HELECTRICITY
    • H01ELECTRIC ELEMENTS
    • H01CRESISTORS
    • H01C1/00Details
    • H01C1/06Electrostatic or electromagnetic shielding arrangements
    • HELECTRICITY
    • H01ELECTRIC ELEMENTS
    • H01CRESISTORS
    • H01C1/00Details
    • H01C1/02Housing; Enclosing; Embedding; Filling the housing or enclosure
    • H01C1/024Housing; Enclosing; Embedding; Filling the housing or enclosure the housing or enclosure being hermetically sealed
    • HELECTRICITY
    • H01ELECTRIC ELEMENTS
    • H01CRESISTORS
    • H01C1/00Details
    • H01C1/14Terminals or tapping points or electrodes specially adapted for resistors; Arrangements of terminals or tapping points or electrodes on resistors
    • H01C1/148Terminals or tapping points or electrodes specially adapted for resistors; Arrangements of terminals or tapping points or electrodes on resistors the terminals embracing or surrounding the resistive element

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  • Engineering & Computer Science (AREA)
  • Microelectronics & Electronic Packaging (AREA)
  • Physics & Mathematics (AREA)
  • Electromagnetism (AREA)
  • Details Of Resistors (AREA)

Abstract

An electrical resistor, particularly of high resistance value, is described comprising an elongate resistor body having electrically conductive terminals 3 extending from ends thereof and having an electrically insulating envelope 5 surrounding the body. An electrically conductive band 7 is provided on, and optionally extending through the thickness of, the envelope at a region intermediate the ends and arranged to substantially surround the resistor body whilst being electrically insulated therefrom. The band is arranged to be connected so as to be maintained at substantially the same electrical potential as one of the terminals 3 when the resistor is connected for operation, and risk of leakage current flow across the surface of the envelope, and optionally through the envelope, is thereby minimised or avoided. <IMAGE>

Description

SPECIFICATION Improvements in or Relating to Electrical Resistors This invention relates to electrical resistors and more particularly to electrical resistors having a high electrical resistance value, e.g. above 106 ohm.
In the preparation of high value electrical resistors having resistance values above about 106 ohm, problems arise with regard to the provision of electrically insulating protective coverings for the resistance element of such a resistor. The element must be especially well protected against moisture and contaminants such as grease or dust since such moisture and contaminants would provide a leakage path for electric current across the surface of the resistor and although this leakage path may be of quite high electrical resistance, its value is significant in relation to the electrical resistance value of the element with which it is effectively connected in parallel.Attempts have been made to overcome these problems by enclosing the resistance element in a sealed envelope, glass being particularly favoured for this purpose, the glass envelope being applied in the form of a tube over the resistance element and sealed to the ends of the element where the terminations emerge.
This approach is not wholly satisfactory, since the surface of the envelope can become contaminated as a result of deposition of airborne moisture, dust or grease. This contaminated surface again provides a high electrical resistance path in parallel with the high value resistance element and significantly affects the measured end to end resistance value of the resistor and promotes resistor instability.
It is an object of the present invention to overcome or minimise the above disadvantages.
The present invention provides an electrical resistor comprising an elongate resistor body having electrically conductive terminals extending from ends thereof, an electrically insulating envelope surrounding said resistor body, said envelope being provided, at a region intermediate said ends, with an electrically conductive band substantially surrounding but electrically insulated from said resistor body, said band being adapted to be connected so as to be maintained at substantially the same electrical potential as one of said terminals when said resistor is connected for operation.
In one embodiment, the said band may be provided on the external and/or internal surface of said envelope and suitably comprises a metal strip or wire, or a layer of electrically conductive material deposited on said external and/or internal surface.
In a further embodiment the said envelope may comprise two portions joined by said band, said band preferably extending throughout the thickness of said envelope.
The said envelope may comprise inorganic or organic material, well known in the art, e.g.
plastics, cements, lacquers, glasses or ceramics.
A preferred material is glass, applied in the form of a tube and sealed to the ends of the resistor body or to the terminals.
Advantageously the resistor has an electrical resistance value of greater than 106 ohm, measured between the terminals.
When the resistor of the invention is connected by its terminals to an electrical circuit such that electric current passes through it, then by connecting the electrically conducting band so that it is maintained at substantially the same electrical potential as one of the terminals of the resistor, substantially no electric current flow can occur across the surface of the envelope between the terminals even although the surface of the envelope may be contaminated with matter which would otherwise provide a high resistance leakage path for electric current. The invention thus constitutes a significant improvement in high value resistor technology.
The invention is now described by way of example with reference to the accompanying drawings in which: Figure 1 shows a perspective view of an embodiment of electrical resistor according to the invention.
Figures 2 and 3 represent sections through alternative arrangements for the resistor of Figure 1.
Referring to Figures 1 and 2, an electrical resistor according to the invention is constructed comprising a resistor body 1 consisting of a cylindrical ceramic substrate having on its surface a film of electrically resistive material, e.g. a film of metal, metal alloy, metal oxide, cermet or carbon, well known in the art. Terminals comprising metal caps 2 and leads 3 are provided, the caps 2 forming an interference fit with the ends of the resistor body 1 and in electrical contact with the resistive film. A helical groove 4 is cut in well-known manner in the resistive film to produce a high resistance value, e.g. 106 to 1014 ohm, measured between the terminals.
An electrically insulating envelope 5, in the form of a glass tube, is slid over the resistor body and sealed to the leads in regions 6 by locally applying heat to cause the glass to melt in those regions.
An electrically conductive band 7 is applied to the external surface of the envelope 5 at a region intermediate the ends of the resistor and such that the band 7 surrounds the envelope 5. The band 7 may comprise wire or metal tape wrapped around the envelope 5 or may comprise a deposited layer of an electrically conductive material such as silver.
The resulting resistor is connected by its leads 3 into an electrical circuit (not shown). An electrical lead (not shown) is also connected to the band 7, e.g. by means of a spring clip, and arranged so that band 7 is maintained at the same electrical potential as one of the leads 3.
The presence of band 7 at this potential means that no leakage of electric current can occur across the surface of the envelope 5, between the leads 3, in the event that the surface of the envelope became contaminated to the extent that a high resistance current leakage path would otherwise occur across the surface of the envelope. Thus substantially all of the current through the resistor is carried by the resistive element of the resistor body regardless of the state of the external surface of the envelope 5.
In some circumstances, leakage of electric current may also occur through the body of the insulating envelope 5 or across the inner surface of the envelope 5. This is overcome or minimised by means of the arrangement shown in Figure 3.
.In Figure 3, parts fulfilling the same or similar functions as those in Figures 1 and 2 are given the same reference numerals as in Figures 1 and 2. In Figure 3, a resistor body 1 provided with terminals comprising metal caps 2 and lead wires 3 is sealed inside a glass envelope 5 as previously described in relation to Figures 1 and 2. The arrangement in Figure 3 differs, however, in that the glass envelope 5 is formed of two parts joined together by metal band 7, the metal band 7 extending throughout the thickness of the glass envelope 5. An example of a suitable material for the band 7 is copper and this band is joined to the two'parts of the glass envelope using conventional glass to metal sealing techniques, well known in the art. The glass envelope and the band 7 are spaced from the surface of the resistor body 1 by means of the caps 2 so that the band 7 is maintained electrically insulated from the resistor body.
The resistor is connected in circuit as previously described with respect to Figures 1 and 2 and the band 7 being connected so as to be maintained at the same electrical potential as one of the terminal leads 3 of the resistor. By means of this arrangement, leakage of electric current is minimised or prevented not only across the external surface of the envelope 5 between the terminal leads but also through the envelope and across the internal surface of the envelope.

Claims (9)

Claims
1. An electrical resistor comprising an elongate resistor body having electrically conductive terminals extending from ends thereof, an electrically insulating envelope surrounding said resistor body, said envelope being provided, at a region intermediate said ends, with an electrically conductive band substantially surrounding but electrically insulated from said resistor body, said band being adapted to be connected so as to be maintained at substantially the same electrical potential as one of said terminals when said resistor is connected for operation.
2. A resistor according to Claim 1 in which said band is provided on the external and/or internal surface of said envelope and comprises a metal strip or wire, or a layer of electrically conductive material deposited on said external and/or internal surface.
3. A resistor according to Claim 1 in which said envelope comprises two portions joined by said band.
4. A resistor according to Claim 3 in which said band extends throughout the thickness of said envelope.
5. A resistor according to any one of the preceding Claims in which said envelope comprises inorganic or organic material.
6. A resistor according to Claim 5 in which said material comprises plastics, cements, lacquers, glasses or ceramics.
7. A resistor according to Claim 6 in which said material is glass applied in the form of a tube and sealed to the ends of-the resistor body or to the terminals.
8. A resistor according to any one of the preceding Claims, having an electrical resistance value of greater than 1 Off ohm, measured between the terminals.
9. An electrical resistor constructed and arranged substantially as herein described and shown in the accompanying drawing.
GB7839025A 1978-10-03 1978-10-03 Improvements in Electrical Resistors Withdrawn GB2032191A (en)

Priority Applications (1)

Application Number Priority Date Filing Date Title
GB7839025A GB2032191A (en) 1978-10-03 1978-10-03 Improvements in Electrical Resistors

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
GB7839025A GB2032191A (en) 1978-10-03 1978-10-03 Improvements in Electrical Resistors

Publications (1)

Publication Number Publication Date
GB2032191A true GB2032191A (en) 1980-04-30

Family

ID=10500065

Family Applications (1)

Application Number Title Priority Date Filing Date
GB7839025A Withdrawn GB2032191A (en) 1978-10-03 1978-10-03 Improvements in Electrical Resistors

Country Status (1)

Country Link
GB (1) GB2032191A (en)

Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0482271A1 (en) * 1990-10-24 1992-04-29 International Business Machines Corporation Current-to-voltage converter with low noise, wide bandwidth and high dynamic range
EP2833372A1 (en) * 2013-07-31 2015-02-04 Forschungszentrum Jülich GmbH Resistor with reduced parasitic capacitance
CN105842508A (en) * 2015-01-12 2016-08-10 苏州华电电气股份有限公司 AC voltage divider

Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0482271A1 (en) * 1990-10-24 1992-04-29 International Business Machines Corporation Current-to-voltage converter with low noise, wide bandwidth and high dynamic range
US5237493A (en) * 1990-10-24 1993-08-17 International Business Machines Corporation Current-to-voltage converter with low noise, wide bandwidth and high dynamic range
EP2833372A1 (en) * 2013-07-31 2015-02-04 Forschungszentrum Jülich GmbH Resistor with reduced parasitic capacitance
CN105842508A (en) * 2015-01-12 2016-08-10 苏州华电电气股份有限公司 AC voltage divider

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Legal Events

Date Code Title Description
WAP Application withdrawn, taken to be withdrawn or refused ** after publication under section 16(1)