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:
Apr. 25, 1989
Filed:
Dec. 18, 1987
Roger A McCurdy, Troy, MI (US);
Dana A Stonerook, Plymouth, MI (US);
TRW Inc., Lyndhurst, OH (US);
Abstract
An impedance measurement circuit and method is disclosed that uses a differential amplifier to amplify a DC voltage value developed across a device being measured. The device is biased between potentials of a source of electrical energy by first and second bias resistors. A switchable current source is connected to the device to, when actuated ON, connect the device to the source of electrical energy through first and second associated resistors. The ratio of the values of the first to second bias resistors is substantially equal to the ratio of the values of the first to second resistors associated with the switchable current source. A microcomputer calculates the resistance of the device by subtracting the value of the output signal from the differential amplifier when the switchable current source is OFF from the value when the switchable current source is ON. The difference is multiplied by a constant having a value dependent upon the gain of the amplifier and divided by a value functionally related to the value of the source of electrical energy. In this manner, the effects of common-mode errors and differential-mode errors are eliminated from a calculation of the resistance value of the device.