Research on Key Technology for Calibrating the Capacity of Spirometer Syringes

To better realize the traceability of spirometer syringes used in spirometry, research on the method of calibrating the capacity of the syringes and the development of a calibration device have been conducted. The volume V₂₀ of the syringes at standard temperature is obtained using the developed calibration device, which is calibrated on the negative pressure principle by measuring the mass of pure water inhaled into the weighing cylinder when the piston rod of the syringe is slowly withdrawn to generate negative pressure. The temperature, humidity, and pressure of the atmosphere in the weighing cylinder and calibration cylinder are measured at the beginning and end of the measurement. The volume of pure water drawn in is calculated as V₂₀₁, the volume of air at the beginning and end of the measurement is calculated by applying the van der Waals equation, and the difference in volume is calculated to obtain a correction value ΔV for the volumetric measurement. The sum of V₂₀₁ and ΔV is V₂₀. Volume measurements were carried out on syringes with nominal capacities of 1 L and 3 L. The repeatability of the results of several sets of measurements was less than 0.06%, and the measurement uncertainty was less than 0.1% (k=2). The difference between the volume measurement results and those of the conventional static weighing method was within 0.05%, confirming that the measurements of the calibrated device were equivalent to those of the conventional static weighing method. The calibration method and calibration device in this paper satisfy the requirements for carrying out capacity calibration for syringes with a capacity measurement requirement of 0.05% repeatability and a tolerance of ±0.5%. They will also provide important technical support for the preparation of the calibration specification for the volume of confined cavities.