Calibration system for draw resistance and ventilation rate standards based on mass flow

In order to avoid the effects of environmental temperature, atmospheric pressure and pipeline pressure drop when calibrating draw resistance and ventilation rate standards based on volume flow, a calibration system for draw resistance and ventilation rate standards was developed based on mass flow. The system takes the downstream gas pressure of draw resistance and ventilation standards and the atmospheric pressure and temperature of the test environment as correction parameters, and generates the constant volume flow required by calibration through a mass flow-adjustable molbox flow terminal, a molbloc-S sonic nozzle and an automatic control unit. The repeatability and stability of the system were tested with the draw resistance and ventilation standards of different specifications and compared with the calibration device based on volume flow. The results showed that: 1) The stability and repeatability of the calibration results of draw resistance and ventilation standards were better when calibration based on mass flow. 2) The absolute value of relative deviation of calibration results of draw resistance standards was no more than 0.21%, and that of ventilation rate standards was no more than 0.05%, which were basically consistent with the calibration results based on volume flow. This technique provides a support for promoting the accuracy of calibration results of draw resistance and ventilation rate standards.