改进取压方式提升音速喷嘴气体流量标准装置的准确度

Improving the accuracy of the standard device for sonic nozzle gas flow by improving the pressure collection method

音速喷嘴气体流量标准装置因其结构简单、性能稳定、准确度较高、无可动部件、维护方便等特点,成为气体流量计量检测的主流标准装置。被检表以及标准器处的气体取压方式有两种:绝压、绝压+差压。通过对装置不确定度评定,测差压的差压变送器量程范围小,降低了最大允许误差;测被检表与标准器处气体的绝压共用同一个绝压变送器,灵敏系数的降低,提高了准确度。同样采用0.2级压力变送器测压的标准装置,前者因压力引起的相对标准不确定度为0.177%,而后者为0.0166%,仅为前者的1/10,装置的扩展标准不确定度Ur=0.24%,k=2,完全满足准确度等级为1.0级气体流量计的检定要求。采用绝压+差压取压方式,在不提高压力变送器准确度等级的情况下,有效提升装置的准确度。该方法简单可行,适用范围广,可应用于其他气体流量标准装置。

Sonic nozzle gas flow standard device is the major standard device for gas meter measurement because of its simple structure,stable performance,high accuracy,no movable parts and easy maintenance.There are two ways to take the gas pressure at the gas meter and the standard device:absorption pressure and absorption pressure plus differential pressure.By evaluating the uncertainty of the device,the range of differential pressure transducer is small and MPE is reduced.The same absorption pressure is shared between the measured meter and the standard device,which reduces the sensitivity coefficient and improves the accuracy.Similarly,0.2 stage pressure transmitter is used,according to the former scheme,the relative standard uncertainty caused by pressure is 0.177%,whereas the latter is only 0.016 6%,which is only 1/10 of the former.The extended standard uncertainty U r of the device is 0.24%,k=2,which fully meets the verification of gas flowmeter with 1.0 grade accuracy.The method of absolute pressure plus differential pressure is adopted to effectively improve the accuracy of the device without improving the accuracy level of the pressure transmitter.This method is simple and feasible,has wide application range,can be applied to other gas flow standard devices.