GB2309905A

GB2309905A - Diacharching static potential differences

Info

Publication number: GB2309905A
Application number: GB9602381A
Authority: GB
Inventors: Peter John Clark
Original assignee: Individual
Current assignee: Individual
Priority date: 1996-02-06
Filing date: 1996-02-06
Publication date: 1997-08-13
Also published as: GB9602381D0

Abstract

A method of discharging a static potential difference between one's person and an adjacent object comprises holding a static discharge device including a discharging circuit with a part of one's hand making electrical connection with one end 1 of the discharging circuit and moving the static discharge device so that the other end 4 of the circuit makes electrical contact with the object, the discharging circuit comprising a resistor 2 and a neon discharge tube 3 connected in series. The discharge may produce visible light in the neon discharge tube. The device may comprise an insulated or insulating body 5 carrying outwardly exposed contacts 1 and 4 with the resistor 2 and discharge tube 3 within the body, the only conductive path between the contacts being through the resistor and the discharge tube. The body may have an opening or window 8 exposing to view at least a part of the discharge tube.

Description

PERSONAL DISCHARGE DEVICE When an object carrying a static electric charge touches or approaches very close to an object which is earthed or which carries a static electric charge of a different potential there is a flow of current of very short duration between the two objects which is commonly called "a discharge". If the difference between potentials is sufficient, the discharge may cross an air gap of 5 mm. or more, often with audible sound and in poorly lit conditions with a visible light.

Static electric charges frequently accumulate on persons and objects as a result of movement. The charges are generated by fiction during movement and if the person or object is not earthed or not readily conductive they can reach a substantial potential. When a person carrying such a charge touches an object which is earthed or carries a charge of a different potential there can be a discharge as described above which can produce an electric shock. This is not dangerous but can be painful or unpleasant. The discomfon caused by such a discharge depends upon the difference between the potentials, which is likely to depend upon the movement which generated the charge. However, it varies between different people in the same circumstances and it can be sufficient to inhibit a person from touching an object in circumstances under which a discharge may be expected without first ensuring that any difference in potentials is discharged.

Amongst objects on which charges commonly accumulate and cause problems of the kind described above are motor vehicles, particularly cars in which seats are upholstered in synthetic materials. To avoid such problems it is common to mount a discharge device on the vehicle in the form of a conductive strip extending downwardly to touch the ground so that any accumulated static electric charge on the vehicle will be dissipated in a discharge whenever the device touches or approaches dose to the ground. However there is no visible sign that discharge has taken place. If the device does not make contact with or approach sufficiently dose to the ground, discharge may not take place and an unsuspecting person may still experience an unpleasant shock on touching the vehicle either when about to enter it or on leaving it.

Persons can therefore lose confidence in such devices. Metallic fittings in buildings, for example central heating radiators are another common source of problems. especially when non-conductive noor covering such as synthetic fibre carpeting is fitted or furniture in the building has synthetic upholstery materials. One usually has no warning of the accumulation of static charges on one's person, just a shock caused by discharge when touching such fittings and other earthed objects.

According to this invention a personal discharge device comprises an insulated or insulating body carrying first and second outwardly exposed contacts and a resistor and a neon discharge tube within the body, the resistor and the neon discharge tube being connected together in series between the two ouwardly exposed contacts, the arrangement being such that the only conductive path between the outwardly exposed contacts is through the resistor and the neon discharge tube, the body having an opening or window exposing to view at least a part of the neon discharge tube.

By a "neon discharge tube" is meant a container, usually at least partly of glass or other transparent or translucent material containing neon and/or other gas at low pressure and spaced electrodes connected terminals outside the container. Such a device may also be called a "spark gap" or a "cold cathode switching tube". The devices are well-known, as is the fact that when the terminals are connected to points at sufficiently different potentials there will be a discharge between the electrodes which produces visible light inthegas.

In use, the personal discharge device described above may be held in the hand with a finger or thumb touching the first contact and the second contact may be placed close to or against an object believed to be carrying an accumulated charge which is likely to cause a shock on discharge. If the potential of any charge carried by the object is significantly different from that of any charge carried by the person there will be a discharge through the neon discharge tube and the resistor which will give a visible light indication in the neon discharge tube which can be seen through the opening or window. The energy of the discharge will be dissipated mainly in the resistor and in partially in the neon discharge tube so that the user will feel little or no shock. A wide range of resistor values may be used, but 1.8 Megohm is satisfactory.

It is acknowledged that testing devices, commonly called "mains testers" and usually incorporated in screwdrivers, are known which comprise a miniature neon discharge tube and a resistor connected in series between a first contact to be touched by a person using the device and a second contact to be placed against a part of a circuit which is suspected to be "live", but such devices are not intended for use for discharging accumulated static charges and are not believed to have been used for that purpose. The circuitry is well known and need not be described further.

The insulated or insulating body of the personal discharge device described above may be formed from insulating material such as a rubber compound or a resin or plastics material such as polypropylene or it may be conductive with an insulating covering and insulation between the body and the first contact and between the terrninals of the neon discharge tube. Preferably it is a moulding in plastics material, produced with the two contacts and the neon discharge tube and the resistor, already connected in series, positioned as an insen in the mould before the plastics material is introduced. The moulding may be in the form of a tag for a key ring or an object for wear such as a pendant or a ring which will always be available to a wearer for use when required. Altematively it could be a loose object or any form of novelty which could be carried in pocket or handbag. The resistor and the second contact may be formed integrally with the moulding or a part of it if the plastics material is conductive. A moulding of conductive plastics material of appropriate resistivity may enclose a miniature neon discharge tube as an insert, revealed though an aperture or window and with one terminal extending into the moulding and the other terminal connected to a first contact which is insulated from the moulding, for example by being mounted in an insulating sheath over the moulding and may be formed with a projecting point or nose extending from the sheath to form the second contact.

An embodiment of the invention is illustrated by way of example by the accompanying drawings in which: Figure 1 is a diagrammatic plan of the circuit of a personal discharge device and Figure 2 is a longitudinal cross section of a personal discharge device made with a circuit as shown in Figure 1.

In Figure 1 a first contact 1 is a disc of conductive material such as copper of shape and size convenient to make conductive contact with a person's finger or thumb, for example circular with diameter 10 mm. One terminal of a resistor 2 is electrically and mechanically connected to the disc 1, for example by soldering and its other terminal is connected to one terminal of a miniature neon discharge tube 3, the other terminal of which is connected to a second contact 4 of conductive material, for example a short brass rod.

Figure 2 shows these components assembled in an insulating body 5 which is a moulding in plastics material such as polypropylene in a form suitable for use as a key-ring tag or for wear as a pendant, having a hole 6 for the purpose. The components, arranged as shown, are inserted in the mould before admitting the plastics material so that after moulding they are permanently enclosed in the body 5. The first contact disc 1 is in the wall of the body which is undemeath in the drawing and its surface which is underneath is exposed in that wall so that it can readily be touched by a finger or thumb when the body S is held in the hand of a person. One terminal of the resistor 2 is soldered to the surface of the disc 1 which is uppermost in the drawing and its other terminal is connected to one terminal of the neon discharge tube 3, for exmple by soldering. The second terminal of the neon discharge tube is connected to the second contact rod 4, the free end of which projects from a point or nose 7 of the body 5. In the part of the body S which is cut away in the drawing there is an opening 8, shown in dotted detail, through which the middle part of the neon discharge tube, particularly the space between its inlernal electrodes, can be seen.

If the device shown in Figure 2 is held in the hand with a finger or thumb touching the first contact disc 1 and the second contact is placed close to or against an object carrying an accumulated static charge at a potential different from that of the person holding it, if the potential difference is sufficient there will be a visible discharge between the electrodes of the miniature neon discharge tube which can be seen through the opening 8. Although the charge flows to or through the person holding the device the resistor will dissipate the majority of the energy, preventing any shock or discomfort. A person seeing the visible discharge will know that the potential difference has been discharged and he or she can safely touch the object. Thus, for example, a person about to open a locked car, carrying the device on a key ring with the car key, can place the second contact against or close to the car lock and see a visible discharge if the potential of any charge on the car was sufficiently different from any accumulated static charge carried by the person. He or she will then know that he or she can then insert the car key into the lock without experiencing any shock or discomfort.

Instead of a one piece moulding surrounding the circuit components as shown in Figure 2 the body 5 may comprise two halves, for example with faces which can be placed together on the plane of the section in Figure 2 and which can be secured together by a stud on one half snapping into an hole in the other half, or by a screw or screws. If a conductive plastics material was used instead of polypropylene then a portion of the body could itself take the place of the resistor 2 and the second contact 4 could also be a part of the body, which could have an insulating sheath to ensure that any discharge would pass though the miniature neon discharge tube. The first contact would also need to be insulated from the casing, for example by having a surrounding collar of insulting material.

Although in the embodiment shown in the drawings the resistor 2 is connected to the first contact 1 and the neon discharge tube 3 is between the resistor 2 and the second contact 4, it will be understood that the positions of the resistor 2 and the neon discharge tube 3 could be reversed without affecting the operation of the device in any way.

Claims

1. A method of discharging a static potential difference between one's person and an adjacent object comprising holding in one's hand a static discharge device including a discharging circuit with a part of one's hand making electrical connection with only one end of the said discharging circuit and moving the static discharge device so that the other end of the circuit makes electrical contact with the object, the said discharging circuit comprising a resistor and a neon discharge tube connected in series, whereby discharge of the static potential difference may be indicated by the production of a visible light in the neon discharge tube.

2. A method as claimed in Claim 1 wherein the static discharge device comprises an insulated or insulating body enclosing the discharging circuit and carrying first and second outwardly exposed contacts electrically connected respectively to the ends of the discharging circuit, the arrangement being such that the only conductive path between the outwardly exposed contacts is through the discharging circuit, the body being designed to expose to view at least a part of the neon discharge tube.

3. A method as claimed in Claim 2 wherein the body is transparent or eranslucent.

4. A method as claimed in Claim 2 wherein the body is opaque and has an opening or window to expose to view the said part of the neon discharge tube.

5. For performing the method chimed in Claim 1, a personal static discharge device comprising an insulated or insulating body carrying first and second outwardly exposed contacts and a resistor and a neon discharge tube within the body, the resistor and the neon discharge tube being connected together in series between the two outwardly exposed contacts, the arrangement being such that the only conductive path between the outwardly exposed contacts is through the resistor and the neon discharge tube, the body having an opening or window exposing to view at least a part of the neon discharge tube.

6. A personal static discharge device as claimed in Claim 5 wherein the insulated or insulating body is formed from insulating material such as a rubber compound or a resin or plastics material.

7. A personal static discharge device as claimed in Claim S wherein the insulated or insulating body is formed from conductive material with an insulating covering and with insulation between the body and the first contact and between the terminals of the neon discharge tube.

8. For performing the method claimed in Claim 1, a personal static discharge device substantially as hereinbefore described and as illustrated by the accompanying drawings.