It has been known in the art to determine the transit path of a pipeline, or like underground conductor such as a wire cable, by means of exciting the underground inductor with an electromagnetic excitation signal which is in turn radiated from the pipeline and using a pair of pipeline straddling antennas to detect and amplify signals for binaural directions into a surveyor's binaural headphone set. See, for example, U.S. Pat. No. 4,112,349--H. J. Weber, Sept. 5, 1978.
A complicated multiple electromagnetic conductor detection device for sensing electrical current in buried pipelines is described in U.S. Pat. No. 4,134,061 --H. S. Gudgel, Jan. 9, 1979.
It has in the past not been feasible to detect and work with simple detected variable amplitude signals, when accurate measurements are needed, because of the variations of signal amplitudes receivable because of pipeline location, foreign buried conductors in the vicinity, and difficulties in instrumentation because of variations of gain, etc.
The underground depth of the conductor has been satisfactorily determined only by means of phase comparison from signals at two vertically spaced antennas and then computing from the phase difference, the depth. However, this process is extremely critical in terms of frequencies used, the phase comparison technique, etc. Thus, the equipment is expensive and not readily suited for rugged field usage. A system of this type is found in U.S. Pat. No. 4,220,913--M. I. Howell et al., Sept. 2, 1980.
Techniques are also known in the prior art for measuring or logging distances over which measurements are taken along an underground pipeline. In this respect, U.S. Pat. No. 4,151,458 issued Apr. 24, 1979 to W. H. Seager, electrically connects a measuring wire line to the pipeline and unrolls it from a reel along the measurement distance. U.S. Pat. No. 2,105,247 issued Jan. 11, 1938 to J. J. Jakosky, unwinds an electrical conductor connected to measuring electrodes advanced along the pipeline and unwound from a reel which rotates to advance a recording strip chart.
In general a system for a manual assist survey of an underground pipeline requires accurate readings and simple operation under various conditions to be encountered in the field. To save manpower and thus time and cost of surveys, calculations should be made automatically and directly and the instrumentation should not require manual judgment, manipulation or adjustment. In particular, skilled operators such as surveyors or mathematicians should not be required.
Thus, it is a general objective of this invention to provide an improved simplified manually positioned automatic pipeline depth and offset location calculating instrument useful for surveying pipelines and the like. Other objects, features and advantages of the invention will be found throughout the description, drawings and claims.