Towards a shock tube method for the dynamic calibration of pressure sensors

Abstract

In theory, shock tubes provide a pressure change with a very fast rise time and calculable amplitude. This pressure step could provide the basis for the calibration of pressure transducers used in highly dynamic applications. However, conventional metal shock tubes can be expensive, unwieldy and difficult to modify. We describe the development of a 1.4 MPa (maximum pressure) shock tube made from unplasticized polyvinyl chloride pressure tubing which provides a low-cost, light and easily modifiable basis for establishing a method for determining the dynamic characteristics of pressure sensors.

Mathematical modelling to support traceable dynamic calibration of pressure sensors

“…Side-wall mounted sensors provide a means of estimating the shock speed, and therefore the expected pressure step. Experiments were carried out in a prototype shock tube at NPL, to test the applicability of shock tube theory in predicting pressure gain across the reflected shock [24]. This work found good agreement between the changes in pressure predicted by ideal gas theory and the changes in observed sensor output, for a number of different gases, shock wave velocities, and driven section pressure magnitudes.…”

“…For example, in [27] it was found that for relatively weak shocks, post-shock oscillations were not eliminated by increasing the tube length (though amplitude of the oscillations could be substantially reduced). Experimental investigations into the effects of non-ideal diaphragm burst were made in the prototype shock tube at NPL [24]. Repeated firings were made with diaphragms of different material; aluminium, brass of varying thickness, and copper.…”

Towards a standard for the dynamic measurement of pressure based on laser absorption spectroscopy

“…[39] Non-uniform rupture of the shock-generating membrane may also occur, affecting the shock wave-front. [11] These and other non-ideal effects will produce pressure and temperature changes that differ from theory. It is important to remember that the shock tube is not the pressure standard (we are not relying on shock tube theory to determine the pressure); we are relying on it only to provide a reproducible and characteristic time-varying pressure that can be interrogated by the spectroscopic system.…”

“…Modern approaches taken to develop the needed standards use modeling of dynamic systems (sensors) or modeling of pressure sources (shock tubes) which are difficult to verify without independent standards or measurements. [11, 13] We propose a fundamentally different method that relies on measuring the quantum mechanical properties of molecules to determine pressure and temperature. Our proposed technique will utilize line-of-site absorption spectroscopy to measure time-varying pressure and temperature in a gas of known concentration, using the unique quantum mechanical characteristics of the molecules as the standard for pressure.…”

“…Later on in this paper we will discuss a shock tube as an aperiodic (non-cyclical) pressure source which has many desirable characteristics for calibrating time-varying pressure sensors; many of the approaches for overcoming the quandary stated above rely on calculating through physical modeling the time dependent pressure of the source (say, the shock tube) or the sensor and assigning an uncertainty to that calculation. [11] This is the approach taken in the current Euramet EMRP IND09, whose goal is the development of traceable dynamic measurement of force, torque, and pressure. [12, 13].…”