Leaks in a pressure calibration system should be as small as possible in order to reduce the pressure difference between the pressure standard and the device under test (DUT). However, a pressure calibration system that is perfectly sealed from the external environment does not exist, and a pressure difference due to leakage can affect the calibration results. This type of effect should be evaluated precisely because DUTs, such as precise digital pressure gauges with resolutions of less than 1 part in 106, are used widely in industry and the pressure difference due to the leak effect is expected to be larger than the resolution of the DUTs. In addition, precise digital pressure gauges for intercomparisons have been used as transfer standards to determine the degree of equivalence of pressure measurement standards among national measurement institutes (NMIs). This paper explores the leak effect using a leak control valve when a precise digital pressure gauge is calibrated using a pressure balance up to 100 kPa in an absolute mode. Experiments were performed according to an applied pressure, leak amount, tube length and pressure media. It is concluded that the uncertainty caused by a possible leak should be included in the uncertainty evaluation of the calibration results.

The cross float (CF) method is well-known for its accurate and reliable results, however the difficulty on performing CF method arises when dealing with insensitive piston of calibrated DWT. In contrary, automatic transducer assisted cross float (TAC) method could be implemented since it does not affected by this condition as it advantages. The used of TAC method could avoid up to 0.008% relative error of effective area at zero pressure and at 20 °C (A0,20) and twice higher error distortion coefficient (b) in case of calibrating insensitive piston of DWT. In addition, the TAC method has another advantage that is save time with consistent result because it can be performed automatically. Once should be consider when using TAC method is the accuracy of pressure transducer. In this case study, the existing pressure transducer owned by National Measurement Standard-National Standardization Agency (SNSU-BSN), could be utilized to perform automatic TAC method in lower pressure range down to 2 MPa that below 10% of its maximum scale, to calibrate low accuracy DWT greater than 0.08%.

An optimized impulse dynamic pressure generator based on a drop-weight method was developed as a secondary standard. The impulse pressure generator was characterized in detail using various parameters in order to obtain a proper reference dynamic pressure, to calibrate a dynamic pressure sensor. Both a hardware filter and a software filter were successfully employed to eliminate unavoidable noise when the impulse pressure was generated. Five variables were considered to optimize the system. A larger effective area piston-cylinder assembly should be used to obtain a faster impulse pressure. To control the peak pressure using a variable drop height is easier rather than drop weight because the change is linearly proportional to the impact speed associated with the drop height. An increase in drop weight causes an increase in duration as well as an increase in peak pressure. In addition, the pressure transmission medium is very important for generating the optimized impulse pressure, so an appropriate fluid choice is required. The viscosity and bulk modulus among the fluid properties are considered as design variables. High viscosity fluids with high bulk modulus can achieve high peak pressures without jittering. The drop weight based impulse pressure generator design and implementation method is proposed based on the detailed characterizations in this study.

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