ASTM E4-16 pdf free download.Standard Practices for Force Verification of Testing Machines.
10. Selection of Verification Forces
10.1 Determine the upper and lower limits of the verified force range of the testing machine to be verified. In no case shall the verified force range include forces below 2(X) times the resolution of the force indicator.
10.2 If the lower limit of the verified force range is greater than or equal to one-tenth of the upper limit, five or more different verification forces shall he selected such that the difference between two adjacent verification forces is greater than or equal to one twentieth and less than or equal to one-third the difference between the upper and lower limits of the verified force range. One verified force shall he the lower limit of the verified force range and another verified force shall he the upper limit. (Fewer verification forces are required for testing machines designed to measure oniy a small number of discrete forces, such as certain hardness testers, creep testers, etc.)
10.3 If the lower limit of the verified force range is less than one-tenth the upper limit, verification forces shall be selected as follows:
10.3.1 Starting with the lower limit of the verified force range, establish overlapping force decades such that the maximum force in each decade is ten times the lowest force in the decade. The lowest force in the next higher decade is the same as the highest force in the previous decade. The highest decade might not be a complete decade.
10.3.2 Five or more different verification forces shall be selected per decade such that the difference between two adjacent verification forces is greater than or equal to one- twentieth and less than or equal to one-third the difference between the maximum and the minimum force in that decade. It is recommended that starting with the lowest force in each decade, the ratio of the verification forces to the lowest force in the decade are 1:1, 2:1, 4:1, 7:1, 10:1 or 1:1, 2.5:1, 5:1, 7.5:1, 10:1.
10.3.3 If the highest decade is not a complete decade, choose verification forces at the possible ratios and include the upper limit of the verified force range. If the difference between two adjacent verification forces is greater than one- third of the upper limit, add an additional verification force.
No’rE 6—Example: A testing machine has a full-scale range of 50(X) N and the resolution of the force indicator is 0.0472 N. The lowest possible verified force is 9.44 N (0.0472 x 200). Instead of decades starting at 9.44, 94.4 and 944 N. three decades, starting at 10, 1(X). and l(XX) N are selected to cover the verified range of forces. Suitable verification forces are 10, 20. 40. 70. 100. 200. 400. 700, 1000. 2000. 3000. 4000. 5.000. Note that the uppermost decade is not a complete decade and is terminated with the upper limit of the verified force range. The 3000 N reading was added because the difference between 2000 and 4000 was greater than one-third of 5(XX). If the alternative distribution of forces is used, the verification forces selected would he 10, 25, 50, 75, 100, 250, 500, 750. 1000, 2500, 3750. 5000.ASTM E4 pdf download.