![]() “It could totally vary, but a typical rule of thumb is that if you do a comparison measurement, you basically lose a factor of four in accuracy every time,” Fedchak says. That may seem like overkill, but it provides a sufficient level of accuracy by the time it gets to the customer. Using lasers, a tape 60 meters long can be measured to an accuracy of 0.1 mm. NIST has a 60-meter “tape tunnel” that calibrates tape measures for customers ranging from oil companies to sports officials and crime scene investigators. Calibrations are no less important for that product. We need to have a measurement services partner that can provide us with the world’s smallest measurement uncertainties.”Īt the other end of the technology spectrum is the humble tape measure. ![]() There are single calibrations that NIST performs for Fluke Corporation that affect hundreds of millions of dollars of manufactured test and measurement equipment. The critical few calibrations that NIST performs have incredible impact. “The measurement services that NIST provides are a critical component of technological advancement in the United States. Gust, chief corporate metrologist for Fluke Corporation in Everett, Washington. “Technology cannot be advanced unless one has the ability to accurately measure it,” says Jeff C. They can push technology to the cutting edge. For example, calibrations can help manufacturers make the best possible products for their customers. The correction is positive if the measured distance is below MSL.Calibrations may sound mundane, but they actually open up a world of possibilities. The correction is negative if the measured distance is above MSL. As ‘h’ is very small compared to ‘R’, it can be neglected. The value of ‘R’ is approximately 6370 km. Note : If L1 = L2 then Cm = d² / L (-ve) Reduction of Length to Mean Sea Level : Tape Correction for Misalignment (always -ve) : It may be noted that when the pull applied is equal to the normal tension, the pull correction and the sag correction cancel each other and the net correction due to both is zero. Θ = angle of slope between the end supports (i.e the angle made by the chord with the horizontal)Īs ‘Pn’ occurs on both sides of the above equation, the equation can be solved by trial and error method. If the ends of the ta[e are not at the same level, the sag correction is given by If ‘l’ is the total length of the tape which is suspended in ‘n’ bays of equal length ‘l1’ W = total weight of tape between the supports. The above equation can also be written as : L1 = length of the tape suspended between the supports. When the ends of the tape are at the same level, the sag correction is given by : Length is always shorter than the curved length. The correction for sag should be applied as the horizontal chord. To = Standard temperature Tape Correction for Sag (Always -ve) :Ī tape is supported at two ends, it takes the shape of a catenary. The correction of pull (Cp) is given by : If the pull applied at the end of the tape during measurement in the field is different from the standard tension at which the tape was calibrated, a correction of pull is required. H = difference in elevations of the end points. Total correction in the measured distance is given as :Ĭs = L – D = L (1 – cos Θ) = 2L sin²Θ / 2 (-) The correction is positive when the actual length is greater than the nominal length and vice versa. The tape corrections used in surveying are as follows :
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