Patent GB-1170699-A (GB)
Title: Method and device for Extensometric Measurement
Inventor: BERNAIX JEAN
IPC: G01B7/24
Filed: 1968-02-16
Abstract: 1,170,699. Measuring linear distortion electrically. COMMISSARIAT AL'ENERGIE ATOMIQUE and SOC. ANON. COYNE ET BELLIER. Feb.16, 1968 [Feb. 17, 1967], No.7764/68. Heading G1N. [Also in Divisions G4 and G5] In the measurement of the distortion of a surface, a magnetic tape is attached to the surface before distortion has taken place and provided before or after attachment with some form of scale. The scale, modified by distortion of the surface is then subsequently read off the tape. The magnetic tape 6, Fig. 1, may either be mounted directly on the surface A or on a flexible rail 1 along which a carriage 3, carrying the reading head 5 on a blade spring 4, runs. For measuring distortion occurring in a small bore hole the carriage (9, Fig. 2, not shown), may be adapted to run inside a flexible tube (7), fixed in the bore hole by mortar (10) or a polymerizable adhesive of epoxy type, and provided with a flattened inner surface (7a) on which the tape 6 is mounted. The carriage may be drawn along the tape by a flexible band (13, Fig. 3, not shown), of invariable length provided with a tape (14) carrying a reference signal. After the tape 6 has been mounted on the wall A of the bore hole, the reference signal, e.g. pulses of constant frequency, read by stationary head (52), is transferred to the tape 6 by head (51). Subsequently the two signals are read simultaneously and may be transferred to a two track tape for subsequent analysis to determine the deformation of the surface A. In a second embodiment the carriage 3 may be provided with a drum (16, Figs. 4, 5, not shown), having flanges 17, covered with a layer of material having a high co-efficient of friction, e.g. neoprene, which are in rolling contact with the rail 1 so that the drum is rotated as the carriage is drawn along. The drum carries a tape (18) provided with a reference signal which is read by head (53) on the carriage, the tape 6 being read by head (51). As before the signal on tape (18) may first be transferred to tape 6 and the two subsequently compared. In an alternative embodiment, the carriage is provided with two reading heads (54, 55, Fig. 6, not shown), spaced a predetermined, fixed distance apart down the length of the tape, which is such that in the undistorted state of the tape the signals read by the two heads are equal. Any distortion of the tape is thus indicated by unequal signals from the two heads. The signal on the tape may be an A.C. amplitude or amplitude and frequency modulated signal, Figs. 7a, 7b (not shown). In a further embodiment the tape may be provided with two tapes 6a, 6b, Fig. 8, the former initially carrying a train of equidistant unitary pulses 26 which are picked up by head 58. The tape 6b is initially provided with a single pulse S which, when sensed by one head 57, causes a second head 56, spaced a fixed distance D ahead, to record a pulse S 1  on the tape 6b. The number of pulses registered by head 58 between the sensing of the pulses So and S 1  by head 57, i.e. in the distance D, is also counted by counter 61 or 62 and, when pulse Si is reached by head 57, is transferred to printer 63. On sensing pulse S 1  the head 56 is caused to record a further pulse S 2  on tape 6b and again the number of pulses 26 in this distance D is counted and recorded. For underwater use the tape may be covered with a silicone base film. The reading heads may be provided with a system of cleaning brushes which preceed them to remove dust &c. from the tape. To prevent reading errors due to wobble of the carriage, two tapes 6 may be provided secured to the edges of rails 1, the mean reading from the tapes being taken. The reading heads may be inductive (as shown) or Hall effect devices.