Dynamic pressure measurements are important in many fields of industry, e.g. combustion engines, aerodynamics, ballistics and turbomachinery. As a first in Europe, VTT MIKES Metrology is now opening a SI-traceable calibration service for dynamic pressures of up to 500 MPa (5000 bar). The development of the calibration system was initiated in a European research project (EMRP Dynamic). After intensive further development and characterisation, the system is now ready for commercial operations, i.e. metrologically traceable calibrations for customers and commercial R&D activities. This system is unique in Europe.
The new dynamic pressure primary standard generates repeatable pressure peaks with peak pressures of 20 MPa to 500 MPa and pulse duration of 2.5 milliseconds. As a primary realisation of dynamic pressure, the system provides the traceability to the SI-system base units of kilogram, metre and second. Based on a thorough analysis and experimental validation, the measurement uncertainty is estimated to be approx. 1.5 % (k = 2) for the peak pressure. The main components of the system are the measuring head, including a piston cylinder assembly and a small pressure chamber filled with glycerol, and the weight. Additional components are an interferometer, a charge amplifier, digital-to-analogue converters, a measurement computer and software. The weight is dropped on the piston, which compresses glycerol inside the chamber, generating a pressure pulse. The displacement of the dropping weight during the impact is measured with a Michelson-type of interferometer setup, and the acceleration of the piston is determined from the interferometer data. The pressure is determined as a function of time from the mass of the weight, the acceleration and the piston cylinder unit effective area, using the well-known relation p = ma / A.
This unique system opens us new possibilities for customer work and co-operation both at national and international levels. MIKES is the first in Europe to offer a truly traceable calibration service for dynamic pressure transducers in this measurement range. The measurement system is now up and running for customer service.
Figure 1. Pulse duration is about 2.5 ms and the peak pressure about 500 MPa.