[54] DEVICE FOR DETERMINING DEPTH AND DIRECTION OF BURIED OBJECTS
[75] Inventor: Shin Yokoi, Osaka, Japan
[73] Assignee: Yokoi Manufacturing Co., Ltd.,
Osaka, Japan
[21] Appl. No.: 762,603
[22] Filed: Sep. 19,1991
[30] Foreign Application Priority Data
May 16, 1991 [JP] Japan 3-141329
[51] Int. CI.' G01V 3/08; G01V 3/10;
G01R 19/00
[52] U.S. Q 324/326; 324/67
[58] Field of Search 324/326, 327, 328, 329,
324/67
[56] References Cited
U.S. PATENT DOCUMENTS 3,991,363 11/1976 Lathrop 324/67
[ii] Patent Number: 5,194,812 [45] Date of Patent: Mar. 16, 1993
FOREIGN PATENT DOCUMENTS 61-210935 9/1986 Japan 324/67
Primary Examiner—Walter E. Snow
Attorney, Agent, or Firm—Griffin, Butler, Whisenhunt &
Kurtossy
[57] ABSTRACT
Apparatus for locating buried objects such as underground pipes, cables or the like where a transmitter (1) generates an alternating current signal which is fed into the object to produce an alternating field emanating from the object, and a receiver (2) locates this radiation to identify the position of the object. A secondary transmitter (T) transmits a reference signal of the same frequency and phase as the original signal, and a signal processor in a receiver (2a) combines the two signals to eliminate the effects of noise.
7 Claims, 6 Drawing Sheets
