Noise measurement in a locating receiver
A method for choosing a frequency to locate an underground object. A locating receiver is provided with a display. The locating receiver scans multiple pre-selected frequencies to determine a noise level, or a signal-to-noise ratio. The locating receiver transmits the chosen frequency to a transmitter, which places the chosen frequency on the underground object to provide an optimal locating frequency.
1. A method comprising:
coordinating frequencies between a signal transmitter and a utility locator;
taking a first measurement with the utility locator at a plurality of frequencies with no signal transmitted by the signal transmitter;
placing a signal on a buried utility with the signal transmitter;
taking a second measurement with the utility locator at at least one frequency while the signal is placed on the buried utility by the signal transmitter;
calculating a signal-to-noise ratio using the first and the second measurement;
choosing a favorable frequency with a favorable quality indicator based upon the first and the second measurement;
thereafter, placing a locate signal on the buried utility with the signal transmitter at the favorable frequency; and
locating the buried utility by detecting the locate signal with the utility locator.
2. The method of claim 1 wherein the signal is placed on the buried utility through direct electrical connection between the buried utility and the transmitter.
3. The method of claim 1 wherein the signal transmitted by the signal transmitter has a variable magnitude.
4. The method of claim 1 in which the favorable frequency is automatically chosen by a processor.
5. The method of claim 1 in which the buried utility comprises a utility wire.
6. The method of claim 1 in which the buried utility comprises a conductive pipe.
7. The method of claim 1 in which the buried utility comprises a non-conductive pipe with a tracer wire.
8. The method of claim 1 further comprising displaying the signal-to-noise ratio at the plurality of frequencies simultaneously.
9. The method of claim 1 wherein the plurality of frequencies are in the range bounded by 250 Hz and 100 kHz.
10. The method of claim 1 wherein each of the plurality of frequencies has a bandwidth range of 2% to 5%.
11. The method of claim 1 in which the second measurement is taken at the same plurality of frequencies as the first measurement.
12. The method of claim 1 in which the second measurement is taken at one of the plurality of frequencies as the first measurement.
13. The method of claim 1 in which the favorable quality indicator is noise level.
14. The method of claim 1 in which the favorable quality indicator is the calculated signal-to-noise ratio.
15. The method of claim 1 in which the favorable quality indicator is a representation of relative noise.
16. The method of claim 1 in which the first measurement is taken simultaneously at the plurality of frequencies.
17. The method of claim 1 , further comprising:
taking the first measurement and second measurement at a first location;
repeating the first measurement and the second measurement at a second location;
determining and choosing a second favorable frequency with a favorable quality indicator based upon the first and the second measurement at the second location; and
placing a locate signal on the buried utility with the signal transmitter at the second favorable frequency while locating the buried utility with the utility locator at the second location.
18. The method of claim 17 , wherein the favorable frequency and second favorable frequencies are different frequencies.