Title of Invention

"A DEVICE FOR MEASUREMENT OF VOLUME RESISTIVITY OF ELECTRO MAGNETIC INTERFERENCE SHIELDING GASKETS"

Abstract

"A device for measurement of volume resistivity of Electro Magnetic Interference shielding gaskets". This invention relates to a device for measurement of volume resistivity of Electro Magnetic Interference shielding gaskets comprising of a pressure pad assembly supported on a base plate; a handle, for varying the pressure on a test gasket; a first or lower electrode connected to said pressure pad assembly and a second or upper electrode connected to said handle through a power screw, a pair of leads connecting said electrodes to ammeter and voltmeter respectively.

Full Text

FIELD OF INVENTION The present invention relates to a device for measurement of volume resistivity of Electro Magnetic Interference (EMI) shielding gaskets. More particularly the device relates to the measurement of volume resistivity of EMI shielding gaskets or seals. PRIOR ART The operation of various electronic devices such as computers, radios, televisions, communication equipment etc results in generation of electro-magnetic radiation with the electronic circuitry of the equipment. Such radiation often develops as a field or transients within the radio frequency band of the electromagnetic spectrum and it is termed as electromagnetic interference or "EMI" as it is being known to interfere with the operation of other proximate electronic devices. To attenuate EMI effects, shielding having the capability of absorbing or reflecting EMI energy are employed. Shieldings not only confine the EMI energy within a source device, they also insulate these devices or other target devices from other source devices. Such shielding is provided as a barrier, which is inserted between the source and the other devices, and is typically configured as an electrically conductive and grounded housing which encloses the device. Most of the housings are provided with removable accesses like doors, panels, covers etc, as circuitry of these devices must remain accessible for servicing. However, between these accesses and corresponding mating surfaces, there may be gaps, which reduce the efficiency of the shielding by providing openings through which radiant energy may leak or even pass into or out of the device. Moreover, such gaps represent discontinuities in the surface and may even generate secondary source of EMI radiation by functioning as a form of slot antenna. EMI shielding gaskets are employed for filling these gaps within mating surfaces of housings and other EMI shielding structures both for maintaining electrical continuity across the structure and for excluding contaminates such as moisture and dust from the interior of the device. Such gaskets are bonded or mechanically attached to one of the mating surfaces and establish a conductive path by conforming under an applied pressure to irregularities between the surfaces. As such, such gaskets must provide electrical surface conductivity even while under compression. These gaskets must be wear resistant and should have capability to withstand repeated compression and relaxation cycles. EMI gaskets typically comprise a resilient core element having gap filling capabilities which is either filled or coated with an electrically conductive element. The resilient core element is formed of an elastomeric thermoplastic materials such as polyethylene, polyvinylchloride etc while the conductive materials for the filler include silver, aluminium, copper, tin etc. Volume resistivity of these gaskets is an important parameter for characterising efficiency of these gaskets in shielding of EMI. Volume resistivity of an EMI shielding gasket at different points of the gasket under different pressures is an important parameter for characterisation of the gaskets as the gaskets may have to operate under different pressures. As such, It is essential to measure the volume resistivity of the gaskets at a particular pressure in order to effectively predict the efficiency of the EMI shielding gaskets. The volume resistivity is defined as electrical resistance between opposite phases of a 1 cm cube of material and is commonly expressed as ohm-cm. The volume resistivity is measured by the following formula. Volume resistivity (in ohm-cm ) = RA / L Where R = observed resistance in ohm A = area of the specimen in cm2 L = thickness of the specimen in cm The conventional method of measuring volume resistivity of a specimen involves measurement of voltage and current across the specimen. However, the conventional instruments, utilised for measurements of volume resistivity, suffer from following disadvantages: Main disadvantage of the conventional instruments for measurements of volume resistivity, known to the prior art, is that these instruments arc not very accurate. Another disadvantage of the conventional instruments for measurement of volume resistivity, known to the prior art, is that these instruments can not measure volume resistivity at different pressures. OBJECTS OF THE INVENTION Primary object of the invention is to provide a device for measurement of volume resistivity of EMI shielding gaskets. Another object of the invention is to provide a device, which has a capability to measure volume resistivity of EMI shielding gaskets at different pressures applied at the EMI shielding gasket. Yet another object of the invention is to provide a device for measurement of volume resistivity of EMI shielding gaskets which has capability to measure volume resistivity of gaskets having any shape and configuration by incorporating provision for interchanging electrodes. Still another object of the invention is to provide a device for measurement of volume resistivity of EMI shielding gaskets, which also has an in-built mechanism for measurement of pressure applied on the test gasket with a provision for zero error correction. Yet further object of the invention is to provide a device for measurement of volume resistivity of EMI shielding gaskets, which has capability to measure volume resistivity at pressures varying from 0 to 150 psi. Still further object of the invention is to provide a device for measurement of volume resistivity of EMI shielding gaskcls which has a provision for varying the pressure applied on the test gasket. Yet further object of the invention is to provide a device for measurement of volume resistivity of EMI shielding gaskets, which has capability to measure volume resistivity of gaskets having different thickness. Still further object of the invention is to provide a device for measurement of volume resistivity of EMI shielding gaskets which has capability to measure volume resistivity very efficiently in a rapid manner. Yet further object of the invention is to provide a device for measurement of volume resistivity of EMI shielding gaskets which has an ergonomic design. Still further object of the invention is to provide a device for measurement of volume resistivity of EMI shielding gaskets, which is lightweight and portable. Yet further object of the invention is to provide a device for measurement of volume resistivity of EMI shielding gaskets, which is cheaper. Yet further object of the invention is to provide a device for measurement of volume resistivity of EMI shielding gaskets, which is cheaper. STATEMENT OF INVENTION According to this invention there is provided a device for measurement of volume resistivity of Electro Magnetic Interference shielding gaskets comprising of: a pressure pad assembly (3) supported on a base plate (2); a handle (7), for varying the pressure on a test gasket (8); a first or lower electrode (4) connected to said pressure pad assembly (3) and a second or upper electrode (4) connected to said handle (7) through a power screw (5), a pair of leads (9,10) connecting said electrodes to ammeter and voltmeter respectively. In accordance with the present invention, there is provided a device for measurement of volume resistivity of EMI shielding gaskets. The proposed device has capability to measure the volume resistivity of EMI shielding gaskets under different pressures. varying from 0 to 150 psi very efficiently, accurately and in a rapid manner. Further, the device has capability to measure volume resistivity of EMI shielding gaskets having any shape and configuration due to the provision for interchangeable electrodes. The device has an ergonomic design and is lightweight, simpler and easily portable. It has an in-built mechanism for measurement of pressure applied on the test gasket with a provision for zero error correction. The pressure applied on the test gasket can be varied in a continuous manner with the simple rotation of lop handle. The device comprises of a pressure pad assembly having facility for measurement of pressure, a pair of interchangeable electrodes with upper electrode connected with the top rotating handle through power screw and a guide pin and the lower electrode connected with the pressure pad assembly. The test EMI shielding gasket is put between these pair of electrodes and the pressure is exerted over it by rotation of the top handle and this applied pressure is measured with the help of a needle and scale provided in the pressure pad assembly. The volume resistivity of a test EMI shielding gasket, at different pressures, is deduced by measuring current through the test gasket for a particular voltage applied across the test EMI shielding gasket. The measurement of volume resistivity of a test EMI shielding gasket, under different pressures applied over it, helps in characterising the effectiveness of the test EMI shielding gasket. Any further characteristics, advantages and applications of the invention will become evident from the detailed description of the preferred embodiment which has been described and illustrated with the help of following drawings wherein, DESCRIPTION OF DRAWINGS Fig. 1 shows the constructional details of the complete device . Fig.2 shows the schematic diagram of the pressure pad assembly of the device . DESCRIPTION OF THE INVENTION WITH RESPECT TO THE DRAWINGS With reference to Fig.l, the device comprises of a calibrated pressure pad assembly (3), mechanically fixed on a rigid base plate (2). The device has a pair of eSjectrodeg (4) having the lower electrode attached with the pressure pad assembly (3) and the upper electrode attached with the top hand through power screw (5) and a guide ring (6). The test EMt shielding gasket (8) can be placed between the pair of electrodes (4), which in turn can be interchanged for measurements on gaskets having different shapes and configurations. The pressure on the test gasket can be varied by rotating the top handle (7), which is ergonomically designed for easy operation. Volume resistivity of the test gasket (8) is calculated by measuring the voltage applied across the electrode blocks (4) and current passing through it. The voltage and current are measured with the help of voltmeter and ammeter. The leads (9) and (10) attached with the electrode blocks are connected to the voltmeter and ammeter respectively. With reference to Fig. 2, with the rotation of the top handle (7), the pressure is gradually exerted on to the gasket as the cylinder (15) slides telescopic-ally over the cylinder (12) with the help of guide pins (1?) & (18) against the spring force provided by the springs (16). As a result of mis, the needle (14) moves upward along the slot, wifh calibrated graduations provided in the cylinder (15) indicating the exerted pressure. The naedle is attached to a lever (11) spring loaded by spring (11) to avoid undesirably deflections and knob (1) facilitates the zero error correction. For measurement of the volume resistivity, the test EMI shielding gasket (8) is placed between the pair of electrodes (4) and the pressure over the test gasket (8) is varied by rotating the top handle (7). The pressure exerted on the test gasket (8) can be measured with the help of position of the needle (14) on the scale provided in the pressure pad assembly (3). The volume resistivity is deduced with the help of following formula by measuring applied voltage across the test gasket (8) through the voltmeter and the resultant current passing through it through the ammeter. Volume resistivity (in ohm-cm) = RA / L Where R = observed resistance in olim A = area of the specimen in cm 2 L = thickness of the specimen in cm Similarly, volume resistivity of the test gasket (8) can be measured for different pressures by changing the pressure on the test EMI shielding gasket (8) by rotating the top handle (7) and measuring the voltage and current across it in the above manner. The measurement of volume resistivity for a range of pressures helps in characterising the effectiveness of the EMI shielding gasket. The present embodiment of the invention, which has been set forth above, was for the purpose of illustration only and is not intended to limit the scope of the invention. It is to be understood that various changes, adaptations and modifications can be made in the invention described above by those skilled in the art without departing from the scope of the invention which has been defined by the following claims: WE CLAIM; 1. A device for measurement of volume resistivity of Electro Magnetic Interference shielding gaskets comprising of: a pressure pad assembly (3) supported on a base plate (2); a handle (7), for varying the pressure on a test gasket (8); a first or lower electrode (4) connected to said pressure pad assembly (3) and a second or upper electrode (4) connected to said handle (7) through a power screw (5), a pair of leads (9,10) connecting said electrodes to ammeter and voltmeter respectively. 2. A device as claimed in claim 1 wherein said pressure paid assembly (3) having an outer cylinder (15) disposed in a slidable and telescopic relationship over an inner cylinder (12) through guide pins (17) and (18) against the spring force provided by springs (16) attached therein. 3. A device as claimed in claim 1 wherein a needle (14) with scales for displaying the pressure exerted on the test EMI shielding gaskets (8) is attached to a lever (11) loaded by spring (13) which is connected with the said guide pins (17) and (18). 4. A device for measurement of volume resistively of Electro Magnetic Interference shielding gaskets substantially as herein described and illustrated herein.

Documents:

1152-del-2000-abstract.pdf

1152-del-2000-claims.pdf

1152-del-2000-correspondence-others.pdf

1152-del-2000-correspondence-po.pdf

1152-del-2000-description (complete).pdf

1152-del-2000-drawings.pdf

1152-del-2000-form-1.pdf

1152-del-2000-form-19.pdf

1152-del-2000-form-2.pdf

1152-del-2000-form-3.pdf

1152-del-2000-gpa.pdf

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