Reliability and Long Term Stability of a Digital Pressure Gauge (DPG) Used as a Standard- A Case Study 115 Reliability and Long Term Stability of a Digital Pressure Gauge (DPG) Used as a Standard- A Case Study JASVEER SINGH, ASHOK KUMAR, NITA DILAWAR SHARMA and A.K. BANDYOPADHYAY National Physical Laboratory (NPLI) Council of Scientific and Industrial Research (CSIR), New Delhi-110 012 * e-mail: ndilawar@mail.nplindia.org [Received: 02.11.2010 ; Revised: 21.01.2011 ; Accepted: 23.01.2011] Abstract The current paper reports the stability of a pressure dynamometer with a full scale pressure of 60 bar over nine years of operation. Since the stability of this digital pressure gauge depends on factors like repeatability, hysteresis, non-linearity, relative deviation etc, a systematic study has been carried out on each of these components. Finally, a comparison of the calibration factors and the estimated expanded uncertainty is made from the collected nine years calibration database. It has been found that the performance of the equipment showed consistent results for about 5 years after which a slight shift in the parameters described above has set in. But, the overall performance of the equipment remains excellent over the period studied within the limit of experimental uncertainty. © Metrology Society of India, All rights reserved 2011. 1. Introduction It is well known that pressure plays a vital role in various industries like petroleum, sphygmo- manometer, automobiles, avionics, nuclear, thermal, pharmaceuticals, domestic appliances etc. In some of these applications of pressure, the accurate measurement of pressure becomes crucial like in case of altimeters, sphygmomanometers etc. As an apex level calibration laboratory in the country, it is our responsibility not only to provide the traceable accurate pressure measurements through our standards but also to help the industries to get an idea about the performance of the instruments on a definite time scale. It is a difficult task as not all but many of the industries are aware of the good laboratory practices (GLP). The performance and long term stability of the artifact or standard is solely dependent on the GLP and therefore our studies would be fruitful only when we find that the laboratory enforces GLP. After a careful study and considering all aspects of GLP, we have selected a couple of laboratories who have been systematically calibrating their DPG over a span of last ten years and out of them, we have selected one such instrument for in depth studies. There are two types of instruments used for pressure measurements - (a) for primary and secondary standards, for which we use Dead Weight Testers (DWT) and different types of Manometers, and (b) for transfer standards, for which we use Digital Pressure Gauges (DPG), Analog Dial Gauges (ADG) etc. [1-2]. The working principles of these two categories of pressure equipments are different and can be seen in ref. (1). However, the transfer standards e.g. DPG and ADG, determine the absolute and relative MAPAN - Journal of Metrology Society of India, Vol. 26, No.2, 2011; pp. 115-124 ORIGINAL ARTICLE