| 摘要 |
1,149,840. Photo-electric thickness measurement. INDUSTRIAL NUCLEONICS CORP. April 27, 1966 [April 27, 1965], No.48094/68. Divided out of 1,147, 946. Heading G1A. In producing a double sheet of plastics material by blowing a bubble of plastics material by means of an extruder having a circular die, rotating the extruder, die or bubble so that any variations in thickness due to imperfect extrusion are distributed around the bubble and then flattening the bubble to form the double sheet, the average thickness of the sheet is measured by either one photo-electric thickness gauge positioned in the centre of the sheet or several such gauges positioned across the sheet to equally divide the perimeter of the sheet. The output or outputs of the gauge or gauges are averaged for a period of time such that all the sheet material produced during one revolution of the extruder, die or bubble is inspected. The more gauges used, the shorter is this time, although the average thickness may be calculated over an integral multiple of this time. The gauge or gauges are maintained in position against changes in the width of the sheet. Infrared or ultraviolet radiation thickness gauges may be used. The speed of the take-up rollers of the sheet or the extrusion process is controlled according to the average thickness value.
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