Inductive amplifier having comb filter

• US 5,577,099 A
• Filed: 11/09/1995
• Issued: 11/19/1996
• Est. Priority Date: 11/09/1995
• Status: Expired due to Term

• Current Assignee: Greenlee Textron Incorporated (Emerson Electric Company)
• Original Assignee: Progressive Electronics, Inc.
• Inventors: Clark, Brian D., Clement, Douglas S.
• Primary Examiner(s): Chin, Wellington
• Assistant Examiner(s): Shankar, Vijay
• Application Number:
  US08/556,197
• Time in Patent Office: 376 Days
• Field of Search: 379/1, 379/2, 379/21, 379/22, 379/26, 379/27, 379/29, 324/66, 324/67, 324/133, 324/145, 324/538, 324/555, 324/556, 324/542, 340/635, 340/657
• US Class Current: 379/21
• CPC Class Codes: G01R 31/60 Identification of wires in a multicore cable
• CPC Class Codes: H04M 3/28 Automatic routine testing ; Fault testing; Installation testing; Test methods, test equipment or test arrangements therefor

Abstract

An inductive amplifier for identifying and tracing wires includes a comb filter for nulling out 60 Hz. power line "hum", as well as harmonics of 60 Hz. The inductive amplifier includes a probe for sensing an input signal. The comb filter includes a time delay circuit for providing a delayed output signal that is delayed by 16.67 milliseconds, or one 60 Hz. cycle, compared to the input signal. The comb filter also includes an inverter circuit for providing an inverted output signal that is 180 degrees out of phase with the input signal. The comb filter further includes a summer for summing together the delayed output signal and the inverted output signal to null out harmonic components of 60 Hz. while passing other signals to the output of the comb filter. The nulling method may also use digital processing techniques rather than discrete circuit components.

Claims

1. An inductive amplifier for detecting and amplifying an electrical tone conducted by one of a group of wires in order to identify and trace a particular wire, the inductive amplifier suppressing noise signals having a predetermined fundamental noise frequency and suppressing noise signals having frequencies that are harmonics of said predetermined fundamental noise frequency, said inductive amplifier comprising in combination:

a. an electrically conductive probe for being placed adjacent a wire under test;

b. an input terminal coupled to the conductive probe for receiving an input signal therefrom;

c. a delay circuit coupled to the input terminal for receiving the input signal and providing a time-delayed output signal, the time-delayed output signal being delayed by a delay period substantially equal to the inverse of the predetermined fundamental noise frequency;

d. an inverting circuit coupled to the input terminal for receiving the input signal and providing an inverted output signal that is not time-delayed relative to the input signal, but which is out of phase relative to the input signal;

e. a summing circuit coupled to the delay circuit for receiving the time-delayed output signal, the summing circuit also being coupled to the inverting circuit for receiving the inverted output signal, the summing circuit adding the time-delayed output signal with the inverted output signal to provide a noiseless output signal; and

f. an amplifier to amplify the noiseless output signal.

2. The inductive amplifier recited by claim 1 further including a bandpass filter for coupling the electrically conductive probe to the input terminal, the bandpass filter limiting the frequencies of signals provided to the input terminal to a preselected range of frequencies.

3. The inductive amplifier recited by claim 2 wherein the preselected range of frequencies includes signals having frequencies between 500 Hz. and 3,000 Hz.

4. The inductive amplifier recited by claim 1 further including a lowpass filter for coupling the noiseless output signal to said amplifier, the lowpass filter limiting the frequencies of signals provided to the amplifier to frequencies below an upper limit frequency.

5. The inductive amplifier recited by claim 4 wherein said upper limit frequency is a frequency below 5,000 Hz.

6. The inductive amplifier recited by claim 1 wherein the predetermined fundamental noise frequency is 60 Hz., and wherein the time-delayed output signal is delayed by a delay period of approximately 16.67 milliseconds.

7. A method of using an inductive amplifier to trace particular wires within a group of wires while suppressing noise within the inductive amplifier, the method suppressing noise signals having a predetermined fundamental noise frequency as well as harmonics of said predetermined fundamental noise frequency, said method comprising the steps of:

a. coupling a tone generator to a selected wire for imparting a desired audio tone within the selected wire;

b. placing an electrically conductive probe of the inductive amplifier adjacent a wire under test to determine whether such wire under test is the selected wire;

c. coupling an input terminal of the inductive amplifier to the conductive probe for receiving an input signal therefrom;

d. creating a time-delayed output signal corresponding to the input signal, the time-delayed output signal being delayed by a delay period substantially equal to the inverse of the predetermined fundamental noise frequency;

e. creating an inverted output signal that is not time-delayed relative to the input signal, but which is out of phase relative to the input signal;

f. summing the time-delayed output signal with the inverted output signal to provide a noiseless output signal;

g. amplifying the noiseless output signal; and

h. driving a speaker with the noiseless output signal to recreate the desired audio tone.

8. A method of using an inductive amplifier to trace particular wires within a group of wires while suppressing noise within the inductive amplifier, the method suppressing noise signals having a predetermined fundamental noise frequency as well as harmonics of said predetermined fundamental noise frequency, said method comprising the steps of:

a. coupling a tone generator to a selected wire for imparting a desired audio tone within the selected wire;

b. placing an electrically conductive probe of the inductive amplifier adjacent a wire under test to determine whether such wire under test is the selected wire;

c. coupling an input terminal of the inductive amplifier to the conductive probe for receiving an input signal therefrom;

d. creating a time-delayed output signal corresponding to the input signal, the time-delayed output signal being delayed by a delay period substantially equal to the inverse of the predetermined fundamental noise frequency;

e. subtracting the input signal from the time-delayed output signal to provide a noiseless output signal;

f. amplifying the noiseless output signal; and

g. driving a speaker with the noiseless output signal to recreate the desired audio tone.