SECONDARY STANDARDS HOW ACCURATE SHOULD THEY BE

摘要

The rapid development of microchips and the advancement in micromachining has opened new frontiers for the design and manufacture of secondary pressure standards. These new techniques have allowed accuracy statements to be made in terms of percent of reading rather than percent of full scale. In the past, these tolerances have only been available at a high price using specialized pressure transducers with limited capability. By the proper selection and use of the new breed of off-the-shelf components, along with a sophisticated firmware program, Volumetrics Inc. has entered this era. The new Secondary Pressure Standard (SPS) embodies these new techniques to provide a secondary standard that has a tolerance of ±0.05% of reading over a temperature range of 0°C to 50°C, and at a reasonable cost. Accuracy is one of the important values defining the characteristic of an instrument and can be presented in a variety of forms. The most common being given as a percentage of the full scale reading. Therefore, with a 100 psi full scale range and a specified accuracy of ±.05% of full scale the deviation allowed is ±0.05 psi throughout the range. Therefore at 50 psi and an allowable error of ±0.05 psi the accuracy would then become ±0.1% and at 10 psi we now have an accuracy of ±0.5%. Therefore it becomes obvious that an accuracy specifying percent of full scale is only achieved at one point, full scale. To correctly define the accuracy of this instrument we can provide a graph as seen in Figure 1.