Abstract
This paper describes the development of lever type Vickers hardness standard machine according to the requirements of ISO6507-3 by NIMT (National Institute of Metrology Thailand). According to ISO6507-3, the standard machine must pass both direct verification and indirect verification. The direct verification requires checking four parameters: test force, testing cycle, indenter shape, and diagonal measuring device. The most difficult parameter to control is the testing cycle. In testing cycle verification, there are three parameters concerned: approach velocity of the indenter shall be 50 μm/s. to 1 mm/s, the duration of application of the test force shall be 13 s to 15 s, and time for application of the test force shall be 6 s to 8 s. The uncertainty of time shall be within ±0.5 s of each parameter. After the machine was modified, the testing cycle of machine can be automatically and precisely controlled by PC with well-designed interface software. The behavior of testing cycle of NIMT Vickers hardness standard machine was detected by using force sensing element and displacement sensor. We can successfully control the approach velocity in 5 μm/s resolutions, the duration of application of the test force and time for application of the test force in 0.1 s resolutions with ±0.5 s uncertainty of measurement.
