| 摘要 |
1534684 Measuring alignment of fibres DEFENCE SECRETARY OF STATE FOR 29 March 1976 [6 Jan 1975] 497/75 Heading G1N A method of measuring the degree of alignment of the fibres in the plane of a mat of nominally aligned electrically conducting fibres which are not in good electrical contact with each other comprises measuring the dielectric constant of the mat in the plane thereof in two mutually orthogonal directions, one direction being parallel with the nominal direction of alignment of the fibres, and comparing the measurements obtained of dielectric constant. A pair of printed circuit boards 10, 20 are disposed to sandwich the mat 30 therebetween. The board 20 is a mirror image of that 10, shown in Fig. 1a and having inter-digitated comb-like electrodes 14, 16, which are aligned with those 24, 26 of the board 20. The electrodes are connected in a bridge circuit to measure the capacitance between electrodes 14 and 16 and between those 24 and 26 in the plane of the mat. Pressure up to ten p.s.i. may be applied to ensure consistent measurements of capacitance. The dielectric constants of the mat measured as above are considerably higher than that of the bulk material of the fibre. Thus for an asbestos fibre the measurements were 135 and 75 parallel and perpendicular to the nominal direction of alignment measured in the plane of the mat, whereas the values found using a parallel plate condenser technique were 8À0 parallel to the fibres and 5À3 perpendicular to them. It is stated that the measured deviation from the ratio, for perfect alignment in a given material, of the values measured parallel to and perpendicular to the nominal direction of alignment indicates the degree of misalignment among the fibres. The arrangements of Figs. 5(a), (b) (not shown) use guard electrodes. To avoid the need to rotate the circuit boards, by 90 degrees relative to the mat or vice-versa, between measurements four sets of inter-digitated electrodes (62, 64, 66, 68) may be provided in two pairs arranged orthogonally of one another, Fig. 4(a) (not shown). For circularly aligned fibres an array of four sets of electrodes are provided on each board with the electrodes of one pair of sets disposed radially (72, 78) and the others (74, 76) disposed in concentric arcs, Fig. 4(b) (not shown). |
