Pressure Calibration of Quarter-inch Working Standard Microphones by Comparison

The Standards and Calibration Laboratory (SCL) in Hong Kong has developed a system for calibration of quarter-inch working standard (WS3) microphones which automates the measurement process and generates digital calibration certificates (DCC) to meet the growing demand for microphone calibration services in Hong Kong. This paper describes (i) the method of determining the pressure sensitivity of a microphone combination unit from 20 Hz to 20 kHz by the comparison technique in accordance with the International Standard IEC 61094-5, (ii) the measurement model and uncertainty evaluation, and (iii) the automatic system which facilitates the calibration process and generation of a digital calibration certificate.

Determination of phase relations of the olivine–ahrensite transition in the Mg2SiO4–Fe2SiO4 system at 1740 K using modern multi-anvil techniques

The phase relations of iron-rich olivine and its high-pressure polymorphs are important for planetary science and meteoritics because these minerals are the main constituents of terrestrial mantles and meteorites. The olivine–ahrensite binary loop was previously determined by thermochemical calculations in combination with high-pressure experiments; however, the transition pressures contained significant uncertainties. Here we determined the binary loop of the olivine–ahrensite transition in the (Mg,Fe)2SiO4 system at 1740 K in the pressure range of 7.5–11.2 GPa using a multi-anvil apparatus with the pressure determined using in situ X-ray diffraction, compositional analysis of quenched run products, and thermochemical calculation. Based on the determined binary loop, a user-friendly software was developed to calculate pressure from the coexisting olivine and ahrensite compositions. The software is used to estimate the shock conditions of several L6-type chondrites. The obtained olivine–ahrensite phase relations can also be applied for precise in-house multi-anvil pressure calibration at high temperatures.

Implementation of Fuzzy Logic Controller for Pressure Sensor Calibration Chamber

Atmospheric pressure is a weather element that must be observed in the field of meteorology. Electronic barometers, aneroid barometers, mercury barometers are generally instruments for atmospheric pressure measurement. The barometer must be calibrated periodically to ensure the performance of the instrument. To achieve the best target uncertainty during calibration, besides using an accurate primary standard barometer, a stable pressure controller is also needed. Pressure calibration media using a pressurised test chamber is more beneficial due to its capability to accommodate all types of pressure sensors. However, pressurise test chamber still requires an operator to control and stabilise pressure inside the test chamber. In this study, fuzzy logic has been programmed into a microcontroller to control the solenoid valve and vacuum pump for regulating air pressure inside a pressurised test chamber automatically. Fuzzy logic changes the solenoid valve states periodically by varying the opening and closing times. The final result of this study is a comparison between the calibration results using pressure controller with fuzzy logic and without fuzzy logic with the same primary standard and unit under test. The result of expanded uncertainty without a fuzzy logic controller is 13.06 hectopascal. Meanwhile, the pressure calibration process using fuzzy logic to control pressure in pressurised test chamber achieve 0.09 hectopascal of expanded uncertainty in 1000 hectopascal pressure value with coverage factor, k=2, and confidence level of no less than 95 %.

Evaluation of Shock Tube Retrofitted with Fast-Opening Valve for Dynamic Pressure Calibration

Accurate dynamic pressure measurements are increasingly important. While traceability is lacking, several National Metrology Institutes (NMIs) and calibration laboratories are currently establishing calibration capacities. Shock tubes generating pressure steps with rise times below 1 µs are highly suitable as standards for dynamic pressures in gas. In this work, we present the results from applying a fast-opening valve (FOV) to a shock tube designed for dynamic pressure measurements. We compare the performance of the shock tube when operated with conventional single and double diaphragms and when operated using an FOV. Different aspects are addressed: shock-wave formation, repeatability in amplitude of the realized pressure steps, the assessment of the required driver pressure for realizing nominal pressure steps, and economy. The results show that using the FOV has many advantages compared to the diaphragm: better repeatability, eight times faster to operate, and enables automation of the test sequences.