GB1526289A - Geophone and method of checking characteristics of the same or of a seismic string comprising such geophone - Google Patents

Abstract

1526289 Geophones SHELL INTERNATIONALE RESEARCH MAATSCHAPPIJ BV 9 Dec 1975 50420/75 Heading H4J [Also in Division G1] A geophone comprises switch means for suppressing take-off of electric signals from output terminals of the geophone when the position of the geophone deviates a predetermined degree from its operative position. As shown in Fig. 1, the switch comprises a housing 36 containing a volume of mercury 37, an electrode 38 connected to one output terminal 17 and a ring electrode 39 connected to the other output terminal 18 such that when the geophone deviates the predetermined degree the terminals 17, 18 are short-circuited. The transducing element is in the form of a vibratably mounted coil 24 arranged in the field of a fixed ring magnet 22. In the embodiment shown in Fig. 5, the transducing element is in the form of a pair of piezoelectric discs 70, 71 acted upon by a spring mass 72, and the switch comprises a ring electrode 92 connected to the output terminal of the disc 70 and a pendulum-like electrode 93 connected to the output terminal of the disc 71 so that these terminals are short-circuited when the geophone deviates the predetermined degree. As described with reference to Figs. 3 and 4 (not shown), the switch may be designed to break a connection between the measuring element and one of the output terminals when the geophone deviates the predetermined degree. For seismic exploration, a plurality of geophones according to the invention are connected in series in a string. By incorporating switches of the type shown in Figs. 1 and 5 in each geophone, the characteristics of each geophone may be tested by positioning all the geophones but one to shortcircuit their terminals and measuring the characteristics of the one geophone. Each geophone is tested in turn in this manner: Alternatively a plurality of geophones according to the invention and having switches of the Figs. 3 and 4 type are connected in parallel to form a string and again each geophone may be tested by positioning all the other geophones to break their connections. As shown in Fig. 6 a plurality of groups 100, 101, 102, of strings of geophones 103-106 are provided for seismic exploration. To check the correct positioning of all the geophones, the electrical resistance of each group of strings is measured and compared with a reference. If the measured resistance of any group deviates from the predetermined value, each string of that group has its resistance measured and compared with a reference value. The string or strings whose resistance deviates from the predetermined value, then has the position of each of its or their geophones checked.