Study On Air Buoyancy Correction In The Measurement Process Of Microgram Mass Standards

Microgram mass standards have widely applications in the small force measurements and the calibration of high accuracy mass comparators. There are two key factors in the air buoyancy correction of the microgram mass standards. They are the air density and the volume of weights. It is very important to study these two key factors in this paper. Based on the STM32F107 VC ARM chip of STMicroelectronics,a new design of the air density measurement device is completed in NIM. RS-485, USB and network interface are added into the circuit to extend the interfaces besides the RS-232 interface. The remote data exchange of the device is realized in the operation process. It is convenient for sensors fixed in the device to be calibrated by the combined switch. The measurement equation of hydrostatic method presented in OIML R111-1 is also been deducted. The measurement method of the microgram mass standards ranging from 50 mg to 500 mg is introduced in this paper. The correction values of microgram mass standards are obtained from the calculation based on the subdivision method. The values from the measurements to be calculated are automatically obtained by one mass comparator. Experimental results show that the standard uncertainty of the microgram weights is less than 0.15 mg.