EP0096558A2
Expired / Lapsed
EP
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Method of and apparatus for measuring phase
Assignee: Plessey South Africa Ltd
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Filing: 1983-06-03
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Granted: —
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Expires: 2003-06-03
Abstract
Abstract A continuous wave electromagnetic distance measuring system comprises a master station 12.3 and a remote station 12.4. A pattern signal having an accurately known pattern frequency is propagated electromagnetically from the master station to the remote station and an auxiliary pattern signal is propogated electromagnetically from the remote station to the master station. Mixing of the pattern and auxiliary pattern signals produces a first comparison signal at the master station and a second comparison signal at the remote station, the comparison signals each having a frequency which is equal to the frequency difference between the pattern and auxiliary pattern signals. The first comparison signal is phase compared with a first reference signal to provide first phase data, and the second comparison signal is phase compared with a second reference signal to provide second phase data. The second phase data is relayed in coded form to the master station. First and second phase data resulting from a plurality of pattern/auxiliary pattern signal combinations is processed at the master station to obtain an accurate indication of the distance between the stations. The pattern signal and the first reference signal are each derived from a first clock signal. Similarly, the auxiliary pattern signal and the second reference signal are each derived from a second clock signal. By selection of suitably stable reference oscillators for producing the clock signals, errors introduced through phase slip between the clock signals can be reduced to negligible proportions. There is disclosed a method of compensating precisely for any such errors by computing and then applying a correction factor. There is also disclosed a method of straddle measuring in which any such errors automatically fall away.
Inventors
- 👤 Jan Schreuder
Bibliographic Details
Application Number
—
Jurisdiction
EP
Data Source
google_patents
Last Synchronized
2026-11-06 12:33
CPC Classifications
G; G01; G01S; G01S13/00; G01S13/74; G01S13/82; G01S13/84
Claims Analysis
Total Claims: 9
Claim 1
Independent Claim
242 words
1 . A method of obtaining a phase measurement representative of the change in the phase difference between the phase signals of two pairs of phase signals having the same comparison frequency, in which a phase measuring operation is carried out on each of two or more successively produced pairs of comparison signals each having the comparison frequency, a first comparison signal of each pair being produced at a first station and the second comparison signal of each pair being produced at a second station spaced from the first station, and in which the results of the phase measuring operations are processed to produce said phase measurement; characterised in that there is generated a first reference signal having a first reference frequency; that there is generated a second reference signal having a second reference frequency suitably close to the first reference frequency; that each phase measuring operation comprises: phase comparing the first comparison signal of the respective pair with the first reference signal to provide first phase data representative of the phase difference between the first comparison signal and the first reference signal; and phase comparing the second comparison signal of the respective pair with the second reference signal to provide second phase data representative of the phase difference between the second comparison signal and the second reference signal; and that said phase measurement is obtained by suitable processing of the first and second phase data provided by the phase measuring operations.
Claim 2
Dependent Claim
242 words
1 . A method of obtaining a phase measurement representative of the change in the phase difference between the phase signals of two pairs of phase signals having the same comparison frequency, in which a phase measuring operation is carried out on each of two or more successively produced pairs of comparison signals each having the comparison frequency, a first comparison signal of each pair being produced at a first station and the second comparison signal of each pair being produced at a second station spaced from the first station, and in which the results of the phase measuring operations are processed to produce said phase measurement; characterised in that there is generated a first reference signal having a first reference frequency; that there is generated a second reference signal having a second reference frequency suitably close to the first reference frequency; that each phase measuring operation comprises: phase comparing the first comparison signal of the respective pair with the first reference signal to provide first phase data representative of the phase difference between the first comparison signal and the first reference signal; and phase comparing the second comparison signal of the respective pair with the second reference signal to provide second phase data representative of the phase difference between the second comparison signal and the second reference signal; and that said phase measurement is obtained by suitable processing of the first and second phase data provided by the phase measuring operations.
Claim 3
Dependent Claim
77 words
A method as claimed in claim 1, wherein: the first phase data of each phase measuring operation is obtained as an average over several cycles of the first comparison signal, the first reference frequency being suitably close to the first comparison frequency; and the second phase data of each phase measuring operation is obtained as an average over several cycles of the second comparison signal, the second reference frequency being suitably close to the second comparison frequency.
Claim 4
Dependent Claim
116 words
A method as claimed in claim 1 or claim 2, wherein the comparison signals of each pair are produced by: causing a pattern signal having an accurately known pattern frequency to be propagated electromagnetically from the first station to the second station; causing an auxiliary pattern signal to be propagated electromagnetically from the second station to the first station; mixing the pattern signal with the auxiliary pattern signal at the first station to produce said first comparison signal; and mixing the pattern signal with the auxiliary pattern signal at the second station to produce said second comparison signal, the comparison frequency being equal to the frequency difference between the pattern frequency and the auxiliary pattern frequency.
Claim 5
Dependent Claim
58 words
A method as claimed in claim 3, wherein each of said pattern signals is derived from a first clock signal, wherein each corresponding auxiliary pattern frequency is derived from a second clock signal, wherein the first reference signal is derived from the first clock signal, and wherein the second reference signal is derived from the second clock signal.
Claim 6
Dependent Claim
183 words
A method as claimed in claim 3 or claim 4, wherein: a said phase measuring operation is carried out at each of times tl, t2, and tx respectively; the phase measuring operations at times tl and tx are each carried out on pairs of comparison signals produced by pattern signals of the same pattern frequency and auxiliary pattern signals of the same auxiliary pattern frequency; and said processing includes, by means of a suitably programmed data processor: computing a correction factor k in accordance with the following equation: where al and bl are the phase differences represented respectively by the first and second phase data provided by the phase measuring operation at time tl; and ax and bx are the phase differences represented respectively by the first and second phase data provided by the phase measuring operation at time tx; and computing said phase measurement in accordance with the following equation: where 0C is the phase measurement; and a2 and b2 are the phase differences represented respectively by the first and second phase data provided by the phase measuring operation at time t2.
Claim 7
Dependent Claim
183 words
A method as claimed in claim 3 or claim 4, wherein : a said phase measuring operation is carried out at each of times tl, t2, and t3 respectively; the phase measuring operations are carried out at equally spaced time intervals so that tl - t2 = t2 - t3; the phase measuring operations at times tl and t3 are each carried out on pairs of comparison signals produced by pattern signals of the same pattern frequency and auxiliary pattern signals of the same auxiliary pattern frequency; and said processing includes computing said phase measurement in accordance with the following equation: where α is the phase measurement; al and bl are the phase differences represented respectively by the first and second phase data provided by the phase measuring operation at time tl; a2 and b2 are the phase differences represented respectively by the first and second phase data provided by the phase measuring operation at time t2; and a3 and b3 are the phase differences represented respectively by the first and second phase data provided by the phase measuring operation at time t3.
Claim 8
Independent Claim
49 words
A method of continuous wave electromagnetic distance measurement in which each of a plurality of phase measurements are obtained in accordance with the method claimed in any one of claims 3 to 6, and wherein the distance between the first and second stations is derived from the phase measurements.
Claim 9
Dependent Claim
14 words
Apparatus adapted to carry out the method of any one of the preceding claims.
References Cited (Backward Citations)
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