Critically operated nozzles are used to generate the highly stable volume flow in the reference standard. Their operating principle is based on the fact that sound velocity is set up in the neck section of an appropriately shaped nozzle on reaching a defined critical pressure ratio. The volume flow is then principally dependent only on the cross-section through which it flows. The volumetric measurement can thus essentially be traced back to a measurement of time. This can significantly reduce the test duration.

In the overall design of the nozzle reference standard, our design engineers were able to provide nozzles that can be independently replaced by the user through the use of innovative clamping technology and freely-configurable removable baseplates (for three nozzles).

In addition, the standard product series can be supplemented later on with additional volume flows (QRLab) or by a second reference standard operated in parallel (QRManufacturer), without taking up any more space.

Connecting additional testing lines (temperature test cabinet, domestic and industrial meters) allows the implementation of all standard requirements.