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High Frequency Ground Insulator

IP.com Disclosure Number: IPCOM000091663D
Original Publication Date: 1968-Apr-01
Included in the Prior Art Database: 2005-Mar-05
Document File: 2 page(s) / 50K

Publishing Venue

IBM

Related People

Spencer, TD: AUTHOR [+2]

Abstract

Whenever a measurement point has two paths to ground, e.g., through internal windings and through a probe, a current ground loop is created which causes voltage shifts at high frequencies. This can produce erratic displays on instruments such as oscilloscopes. Inductive device 10 permits an instrument, for example, oscilloscope 12, to measure low-level, high-frequency signals without the necessity of isolating the instrument from ground to prevent undesired ground loops. Thus a potential safety hazard is eliminated. In addition, device 10 acts to significantly attenuate high-frequency noise transients.

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High Frequency Ground Insulator

Whenever a measurement point has two paths to ground, e.g., through internal windings and through a probe, a current ground loop is created which causes voltage shifts at high frequencies. This can produce erratic displays on instruments such as oscilloscopes. Inductive device 10 permits an instrument, for example, oscilloscope 12, to measure low-level, high-frequency signals without the necessity of isolating the instrument from ground to prevent undesired ground loops. Thus a potential safety hazard is eliminated. In addition, device 10 acts to significantly attenuate high-frequency noise transients.

Device 10 has a nonconductive body member 13 in which are encapsulated first and second torroidal wound cores 14 and 16. A 3-wire receptacle 18 is mounted in body 13 to facilitate connection of device 10 between a power line and instrument 12. Ground lead 22 is connected to coil 15 of approximately 40 turns on core 14. Power leads 24 and 26 are connected to core 16. The latter has two separate bucking windings 30 and 32 each having approximately 20 turns. Power leads 24 and 26 are separately connected to capacitors 27 and to windings 30 and 32 respectively.

In operation, the instrument's ground lead is connected through coil 15 to ground, and hence the instrument's frame is grounded, while isolating high- frequency noise that may otherwise exist in the grounding system. Winding 15 thus permits accurate measurements to be made without...