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OCR for page 28
APPENDIX B MEASUREMENT OF TEMPERATURE DISTRIBUTION ON HOT PLATE A suitable piece of apparatus for measuring the tem- perature distribution across the hot plate is illustrated in Figure B-1 . The measuring element is to consist of a find thermocouple with the junction flattened and brazed to a disc of copper or brass foil 5 mm in diameter. This is to be placed at a measuring point and covered with a piece of insulating material (asbestos mi11board) 5 mm in thickness and 10 to 15 mm in diameter and held by a vertical glass rod which moves freely in a tubular guide and to which a fixed load is applied. Temperature measurements are to be made along two dia- meters at right angles and at points 20 mm apart and record- ed as in Figure B-2. The thermocouple must be allowed to reach a steady temperature at each point. The measured surface temperature usually will be lower than the set point temperature of the pa ate depending on the detailed construction of the thermocouple. This is im- material and can be ignored. The essential requirement is an accurate measurement of temperature differences rather than of absolute values.

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/ / / / / - --1 1 1 344 346 342 30 Plate Temperature: 350 Scale 1:1 343 - 345- 345 - 346- \ \ \ % \ \ \ \ \ \ \ \ % \ 340 ~ 6 347 FIGURE B-2 - ~ - 346- I I 1 ~ ~ ~ C / /