Chi Kah Lim, Bernd Glöckner, Thomas Allgeier
SHORT AND LONG-TERM BEHAVIOUR OF A 55 kN / 2.2 MN LEVER DEADWEIGHT FORCE STANDARD MACHINE
This paper describes the latest results from the re-verification of a 55 kN / 2.2 MN lever deadweight force standard machine at SPRING Singapore. For the first time, a lever machine was successfully compared against deadweight machines (from PTB) at the high level of 2 MN in both tension and compression with an uncertainty in the 1E-4 range. Similarly, the same applies to the 55 kN machine with an uncertainty of ±2E-5. For the 55 kN machine, both short-term and long-term uncertainty has been established. The machine had been the subject of an earlier comparison measurement with the PTB in the compression range. In addition, the periodic maintenance results of this 55 kN / 2.2 MN lever deadweight force standard machine will also be discussed. To monitor the drift and stability of the force realised, a total of 5 SPRING FTS were measured according to fixed protocols over time. The lever amplification ratio was also checked at intervals using a 50 kN FTS. From an earlier maintenance check, it was discovered that there was a significant drift in the lever ratio in March 2003 (12 months after commissioning). However, the deadweight forces continued to be realised within the ±2E-5 uncertainty. The lever ratio has since been adjusted back to producing loads which are magnified exactly 40 times from deadweight forces, demonstrating that it is capable of achieving ±1E-4 short term uncertainty. This was confirmed by the comparison with PTB up to 2 MN in both loading directions. Subsequent measurements demonstrated that the lever ratio has been stable. The same is also true for load reproducibility and repeatability at both the deadweight and lever machine, indicating that the long- term uncertainty is now satisfactory as well.
