The patent badge is an abbreviated version of the USPTO patent document. The patent badge does contain a link to the full patent document.
The patent badge is an abbreviated version of the USPTO patent document. The patent badge covers the following: Patent number, Date patent was issued, Date patent was filed, Title of the patent, Applicant, Inventor, Assignee, Attorney firm, Primary examiner, Assistant examiner, CPCs, and Abstract. The patent badge does contain a link to the full patent document (in Adobe Acrobat format, aka pdf). To download or print any patent click here.
Patent No.:
Date of Patent:
May. 23, 1995
Filed:
May. 03, 1993
Glade B Bacon, Everett, WA (US);
John Fluke Mfg. Co., Inc., Everett, WA (US);
Abstract
A coupling circuit for a multimeter adapted to perform multiple measurements includes a thermistor and constant current sources in series between an instrument input terminal and an instrument circuit adapted to source current for ohms measurements. Varistors shunt the constant current sources and are thermally coupled to the thermistor. An initial inrush of current is controlled by the constant current sources and when the voltage across a constant current source reaches the knee voltage of the paralleled varistor, the varistor shunts the constant current source and provides heat to the thermistor for insuring the latter will transition to its high resistance state. The thermistor then drops a substantial part of the input voltage, effectively disconnecting the low impedance ohms circuit from the input terminals and protecting the constant current source circuitry and varistors from extended application of high voltage.