Abstract
A new method to calibrate a critical nozzle against the other two, which have been already calibrated, was developed. The method bases on the linear dependency of the pressure between nozzles connected in series on the ratio of their flow rate. Two reference nozzles and the one under test are connected in turn at the upstream of another arbitrary critical nozzle to compare the pressure between the nozzles. The flow rate can be calculated from a linear interpolation between the two reference flow rates by using the difference of the pressure between the nozzles. No instruments other than a pressure gauge, which must be linear in a narrow pressure range, are required, that is, the system need few procedure to keep its accuracy for a long period. An analysis showed that the uncertainty of the method was almost the same as that of the reference nozzle. This was demonstrated by a realized system by calibrating the nozzles which have been already calibrated by a constant volume tank system. The system is fully automated except for installing the nozzle under test and so efficient that one calibration takes only about 10 minutes.
