Objective The aim is to decrease the measurement uncertainty from 0.05%-0.07% to 0.05% for low-medium pressure mass-time primary standard device, so as to further improve the technical level of traceability system.

Methods Through the weight analysis of the factors affecting the measurement uncertainty, the measures such as the improvement of the electromagnetic balance technology, the optimization of the stagnation temperature measurement method and the control of the ambient temperature and humidity were proposed for the main measurement uncertainty. The measurement uncertainty of mass flow of the device was evaluated and the preliminary performance tests were carried out.

Results The uncertainty of the calibration result of the electromagnetic balance was optimized from 1.0 g to 0.5 g; The measurement uncertainty of stagnation temperature was optimized from 0.034% to 0.024%; The uncertainty introduced by environmental temperature and humidity is optimized from 0.02% to 0.01%; The measurement audit result is less than 1.

Conclusions After technical transformation, it is feasible to achieve 0.05% (k=2) of the mass flow measurement uncertainty in the full range of 0.3-6.0 MPa of the low-medium pressure mass-time primary standard device.