Portable electro-magnetic field detection and measurement apparatus for near-field test and measurements

• US 5,773,974 A
• Filed: 04/13/1995
• Issued: 06/30/1998
• Est. Priority Date: 04/13/1995
• Status: Expired due to Term

• Current Assignee: Desco Industries Incorporated
• Original Assignee: Credence Technologies, Inc. (3M Company)
• Inventors: Kraz, Vladimir
• Primary Examiner(s): Snow, Walter E.
• Assistant Examiner(s): Patidar, Jay M.
• Application Number:
  US08/421,802
• Time in Patent Office: 1,174 Days
• Field of Search: 324/258, 324/260, 324/133, 324/67, 324/72, 324/72.5, 324/95, 324/119, 324/120, 324/127, 324/149, 324/244, 324/251, 324/344, 324/345, 340/551, 340/600, 340/815.4, 340/326, 340/547, 250/250, 455/226.2, 455/226.4
• US Class Current: 324/258
• CPC Class Codes: G01R 29/0871 Complete apparatus or systems; circuits, e.g. receivers or amplifiers G01R29/0878, G01R29/0892 take precedence; dosimeters, warning devices G01R29/0857

Abstract

Apparatus for detection of the electro-magnetic field and measurement of its strength in the near field. The apparatus includes an antenna suited to receive specified type of the electro-magnetic field; a detector to convert received signal into DC voltage, a summing device and a potentiometer to set the reference level, a DC amplifier for amplification of resulting signal. The apparatus further includes a voltage-controlled oscillator and a speaker that produces an audible tone with the pitch proportional to the field strength. The apparatus further includes a squelch circuit that blocks the sound when the field strength gets lower than the preset range. The apparatus further includes LED level bar as visual means of indicating field strength. The apparatus is constructed as a fully self-contained unit needing no additional equipment for its operation.

Claims

1. Hand-held apparatus for detecting and measuring the near-field strength of an electromagnetic field, said apparatus comprising:

receiving means for detecting and converting broad-band electromagnetic field radiation into alternating-current signals representing said broad-band electromagnetic field radiation;

signal conversion means, coupled to the receiving means, for converting said alternating-current signals into direct-current signals; and

signal strength indicating means, coupled to the signal conversion means, for indicating the magnitude of the strength of said electromagnetic field radiation in response to said direct-current signals;

said signal strength indicating means including a voltage-controlled oscillator, having a reference voltage, for converting said direct-current signals having a magnitude greater than the reference voltage into an alternating-current signal having a frequency directly proportional to the magnitude of said broad-band electromagnetic field radiation.

2. Apparatus as in claim 1 wherein the signal strength indicating means further includes transducer means coupled to said voltage-controlled oscillator for producing an audible signal having variable pitch for representing variations in the magnitude of the strength of the electro magnetic field radiation in proportion to the pitch of the audible signal.

3. Apparatus as in claim 2 further including level adjustment means, coupled to said voltage-controlled oscillator, for adjusting the reference voltage for causing the frequency thereof to represent a preselected strength of the electro-magnetic field radiation.

4. Apparatus as in claim 3 further including squelch means, coupled to the voltage-controlled oscillator, for inhibiting the transducer means from emitting said audible signal if the magnitude of said direct-current signal is below said reference voltage.

5. Apparatus as in claim 2 wherein a higher magnitude of the strength of the electromagnetic field radiation is indicated by a higher pitch audible signal.

6. Apparatus as in claim 1 further including visual indicating means, coupled to the signal converter means, having a plurality of light-emitting diodes for visually indicating the magnitude of the strength of the electromagnetic field radiation as a function of the direct-current signal.

7. Apparatus as in claim 6 wherein the visual indicating means also indicates variations in the magnitude of the strength of said electromagnetic field radiation.

8. Apparatus as in claim 6 wherein a higher magnitude of the strength of the electromagnetic field radiation is indicated by a higher number of powered light-emitting diodes of the plurality thereof.

9. Apparatus as in claim 1 wherein said receiving means includes an electric field antenna for receiving the electric field component of the electromagnetic field radiation.

10. Apparatus as in claim 1 wherein said receiving means includes an inductive antenna for receiving the magnetic field component of the electromagnetic field radiation.

11. Apparatus as in claim 1 wherein said receiving means includes an electric field antenna, an induction antenna, and switching means for selecting one of said electric field or induction antenna.