Patent GB-566591-A (GB)
Title: Improvements in or relating to apparatus for measuring the degree of roughness of a surface
IPC: G01B7/34
Filed: 1943-06-17
Abstract: 566,591. Electric measuring systems. KAPELLA, Ltd., and REASON, R. E. June 17, 1943, Nos. 9748 and 20451. [Class 40 (i)] [Also in Groups XIX, XXXVI and XXXVII] Apparatus for gauging surface roughness, of the type in which a measure of the average roughness is obtained, comprises means whereby two or more such average readings can be obtained, one being determined by a range of frequencies excluding those due to undulations or irregularities of long wavelength, while the other or others are determined by ranges of frequencies including the long wavelengths. As shown in Fig. 1, an oscillator A<2> feeds a bridge comprising two coils, the inductances of which are varied differentially in known manner as the usual stylus traverses the test-surfaces. The output of the bridge is amplified at A<3>, rectified at A<4> and passed through a filter circuit A<5> to a further amplifying valve B, the anode circuit of which comprises two condensers D<2>, D<1> in series with an integrating meter C which is cut in and out of circuit at appropriate time intervals by contacts B3 as the stylus traverses the work. The meter thus indicates the average amplitude of the higher frequencies. By cutting out the condenser D<1> with the switch D, the meter is made to respond also to the slower vibrations. In Fig. 2, an additional switch D<3> cuts out part of the grid resistance to reduce the amplification of the valve B by an amount equal to the increase of range of frequencies fed to the meter whereby a direct comparison can be made between the roughnesses lying within the different frequency ranges. The output of the valve B may pass to the meter C direct in one case, or through a transformer in the other position of the switch, Fig. 3 (not shown). A ganged switch may cut out a series condenser and put in a shunt condenser, Fig. 4 (not shown). In Fig. 5, the two readings are obtained simultaneously by having two valves B<4>, B<5> in parallel feeding two meters C2, C<3>. Alternatively, a single valve may feed two meters with different tunings, Fig. 6 (not shown). A switch may cut out part of the filter circuit, Fig. 7 (not shown). Three or more readings may be obtained, Fig. 8, by switching in different tuning circuits, also Fig. 9 (not shown), to the meter or different filter circuits to the valve, Fig. 10 (not shown). The switches may be arranged, Fig. 11, so that depression of any switch P<4> automatically releases those previously held depressed by rocking a spring- pressed bus-bar Q, the shoulder Q<2> of which latches over a projection P<6> on the depressed key. The bus-bar may be locked to maintain a key setting by rotation of a plate Q<3> controlled by a lock of the type known under the Registered Trade Mark " Yale." As an alternative to the circuit variations, the speed of traversing the stylus may be varied, Fig. 12, by varying the pivotal point T of a camoperated lever S<4> operating the pick-up head R<1>. The position of the pivot and therefore the speed of traverse is indicated on a scale T<4>. Specification 539,272 is referred to.