Patent GB-1207241-A (GB)
Title: Method of and apparatus for detecting local irregularities in strip and for controlling the evenness of strip
IPC: G01B15/04
Filed: 1968-03-19
Abstract: 1,207,241. Radar. SUMITOMO METAL INDUSTRIES Ltd. 19 March, 1968 [30 March, 1967], No. 13245/68. Heading H4D. The Specification describes a CW Radar type system for determining irregularities in the surface of a metal strip on a rolling mill wherein signals corresponding to said irregularities are used to adjust the crown rollers of the mill to smooth out said irregularities. The strip may be irradiated at the middle and at each edge. Fig. 3 shows the arrangement for one of said positions whilst Fig. 6 (not shown), shows the arrangement for all three said positions. A reflex klystron 1 produces a carrier wave at 9À375 Mc/s pulse modulated at 1000 c/s by a square wave 28. Part of the output is diverted to a resonant cavity frequency meter 26 with a crystal load, but most is fed via alternator 29 and circulator 3, to a horn radiator 4 situated at a height d above the metal strip 5. Part of the oscillator output is also diverted by coupler 2 to form a reference wave at points 15, via variable alternator 29 and phase shifter 11. The echo signal from the strip is received by the horn 4 and passed via the circulator 3 to point 13. The reference wave at 15 and the echo signal at 13 are each equally divided into two channels (E 1  and E 2 ) each comprising a Magic T junction 6 and 14 and square low detector diodes 7, 8 and 16/17. A 90 degree phase shifter 12 is provided in channel E 2 . If the phase difference between the echo signal A Cos (wt.) and the reference wave B Cos (wt. + #) is #, the outputs from the diodes 16 and 17 will be Similarly the outputs from the diodes 7 and 8 will be. In Fig. 5, which shows the processing of the above signals, signals V 1  and V 2  are applied to each end of a transformer primary and the difference signal K.Cos # appears at the output of amplifiers 32. # = 4#d/#, where # is the wavelength of the carrier, so that said difference signal varies with distance d as shown in Fig. 2 and Fig. 7 (A). A range multiple of #/4 is thus produced. With a carrier frequency of 9À375 Mc/s, the range multiple becomes 8 mm. The distance d is therefore measured in units of 8 mm. and the number of cycles of variation in the difference signal is counted as d varies with a strip irregularity. Waveform (A) is thus converted into a square wave (B) in threshold amplifier 35 and differentiated at 38 to produce (C). Signals V 3  and V 4  similarly produces a difference signal K.Sin #, (X) Fig. 7, at the output of amplifier 42 and this is squared in threshold amplifier 45 to produce a gating signal (Y). This is used to gate out the negative pulses in output (C) by means of gate 48, to produce waveform (D). The process is repeated in means 37, 39, 49, 47, but with signals A<SP>1</SP> and X<SP>1</SP> being the inversions of A and X respectively. This produces waveform (D<SP>1</SP>) such that the sum input to pulse counter 50 is waveform (E), wherein each pulse represents only 4 mm. A digital to analogue converter 51 changes the counter output signal to one suitable for controlling the mill crown rollers.