초록 ▼

A portable device for locating a wall stud or similar object positioned behind a wall surface comprises means for detecting a change in the dielectric constant of the wall due to the presence of a stud or similar object and, in combination therewith, means for detecting the presence in the wall of a

A portable device for locating a wall stud or similar object positioned behind a wall surface comprises means for detecting a change in the dielectric constant of the wall due to the presence of a stud or similar object and, in combination therewith, means for detecting the presence in the wall of a source of alternating current. In addition, a display is provided for visually indicating the presence of a source of alternating current in the wall in response to a signal from the means for detecting. The circuit also includes an amplifier to compensate for variations in characteristics of the electrical components used in the structure and an improved circuit for bleeding a bias charge used to calibrate the device when the device is shut off while preventing this charge from being bled when the device is turned on, and structure for indicating to the user that the device is being calibrated.

대표청구항 ▼

A portable device for locating a wall stud positioned behind a wall surface comprising: a first capacitor plate; a pair of second capacitor plates located one on each side of said first capacitor plate and in substantially the same plane as said first capacitor plate; means for conducting a charge t

A portable device for locating a wall stud positioned behind a wall surface comprising: a first capacitor plate; a pair of second capacitor plates located one on each side of said first capacitor plate and in substantially the same plane as said first capacitor plate; means for conducting a charge to said first capacitor plate; means for conducting a charge to said pair of second capacitor plates; means for producing an intermediate output signal representative of the change in the relative capacitance between said first capacitor plate and said pair of second capacitor plates in response to said first capacitor plate and said pair of second capacitor plates being moved along said wall surface; means, responsive to said intermediate output signal, for adjusting the amplitude of said intermediate signal to compensate for variations in the characteristics of said means for producing; means, responsive to said intermediate output signal, for displaying any change in relative capacitance between said first capacitor plate and said pair of second capacitor plates; means for automatically calibrating said device including: means for supplying a calibration charging current to said pair of second capacitor plates; means for detecting when said intermediate output signal caused by said calibration charging current exceeds a selected threshold value; means for holding said calibration charging current constant when said intermediate output signal reaches said threshold value; means for indicating that said calibration charging current is increasing during the calibration of said device; means for resetting said means for supplying said calibration charging current comprising a normally on MOS device which provides a low impedance current path to reset said means for supplying a calibration charging current when said device is shut off and which provides a high impedance path to prevent the resetting of said means for supplying when said device is turned on; means, responsive to said intermediate output signal, for detecting the presence of a line carrying alternating current behind the surface of said wall comprising: bandpass filter means for rejecting those components of said intermediate output signal not in the range of frequency of said alternating current and for amplifying those components of said intermediate output signal in the range of frequency of said alternating current; means for rectifying the signal amplified by said bandpass filter means so that the presence of said line carrying alternating current is detected when said rectified signal exceeds a selected value; and means for indicating that the presence of a line carrying alternating current is being detected by said means for detecting.