[1] Pontius, P. E., The measurement assurance program - a case study, part I, short gage blocks (0.1 to 4 inches), Nat. a case [2] Pontius, P. E., The measurement assurance program [3] Bruce, C. F., Australian J. Phys. 8:224 (1955). [4] Thornton, B. S., Australian J. Phys. 8:241 (1955). [5] Mielenz, K. D., et al, Appl. Opt. Vol. 7, No. 2:289 (1968). [6] Schweitzer, W. G., et al, Appl. Opt. Vol. 12, No. 12:2927 (1973). [7] Riddle, J. L., et al, Platinum resistance thermometry, Nat. Bur. Stand. (U.S.), Monogr. 126 (1973). [8] Handegord, G. O., et al, Humidity and Moisture, Vol. I, Reinhold Publ. Corp., N.Y., 265 (1963). [9] Hedlin, C. P., Humidity and Moisture, Vol. I, Reinhold Publ. Corp., N.Y., 273 (1963). [10] Edlén, B., Metrologia, Vol. 2, No. 2, 71 (1966). [11] Wexler, A. and Hasegawa, S., Relative humidity relationships of some saturated salt solutions, J. Res. Nat. Bur. Stand. (U.S.), Vol. 53, No. 1:19 (1954). Calibration Schedule The apparatus used in the measurement of gage blocks during the period covered by this paper were calibrated and verified as follows: 1. Lasers Laser No. 109: Ao was determined just before period A. Two previous determinations were made 19 and 18 months, respectively, before the start of this study. Variations in λo of 1 part in 108 were observed among the three calibrations. The plasma tube in this laser failed during period G. Laser No. 184: lo was determined just before period H and again before period Q. A change of 13 parts in 108 occurred between cali brations. Iodine stabilized laser: lo was taken from published results [6]. The o of this laser will not change from the published value and its stated uncertainty as long as it is stabilized to the selected absorption line of iodine. 2. Hygrometer ༣. The unit was calibrated by the manufacturer to within + 1.5% RH just Aneroid barometer Biweekly comparisons were made with a reference aneroid barometer maintained by the Pressure and Vacuum Section of NBS until period E. After period E comparisons were made with the reference barometer each time the control standard gage blocks were measured. During periods P and R several comparisons were also made with a fixed cistern mercury barometer. The accumulated data were used to calculate a mean correction to the aneroid. Only once (period D) did the mean correction change significantly. The SPRT, bridge, and thermocouples were calibrated just before period A. After rebuilding the system between B and C the bridge, thermocouples, and SPRT ice point were calibrated. Between G and H, and between P and Q, the SPRT ice point was redetermined, and the bridge was checked against a standard resistor. No significant changes were observed. t At the end of the study a further verification of the system was made. Two resistance bridges were used to measure temperature t of the insulated copper block with the SPRT. The first was the system Mueller bridge and the second was a high resolution a.c. bridge provided by the NBS Temperature Section. The procedure used was to measure R of the SPRT with both bridges (called A and B) in an A B B A sequence to compensate for the effect of temperature drift. Then the SPRT was placed in a triple point of water cell and R was measured with both bridges. Resistance ratio R/R and temperature t were computed from both sets of data and the SPRT Constants. The average difference was 0.0004°C and the values had a range of 0.0003°C. A test was also conducted to determine thermocouple effectiveness. Thermocouples were inserted into the holes of several blocks as described in Section 5 and, in addition, thermocouples were attached to the outside of the blocks with magnets. After overnight stabilization in the interferometer, the maximum difference observed between inside and outside block temperature was 0.0002°C and this value was not exceeded during three days of observation. Under adverse conditions, however, thermal contact between the thermocouples and the wall of the hole might need improving. Library of Congress Catalog Card Number: 75-619353 16. ABSTRACT (A 200-word or less factual summary of most significant information. If document includes a significant bibliography or literature survey, mention it here.) The interferometric transfer of the length unit from its 17. KEY WORDS (six to twelve entries; alphabetical order; capitalize only the first letter of the first key word unless a proper name; separated by semicolons) Calibration; gage blocks; interferometry; laser; length; measurement process; uncertainty. |