A wireless reference node to provide self-calibration capability to wireless sensors networks

Wireless sensors networks (WSNs) are constantly expanding their application field, from simple two-state measurements (e.g., on/off, proximity detection, etc.) to distributed many-parameter measurements. Commercial WSNs offer a wide range of functions and performance with sensors sometimes achieving accuracy comparable with desktop instrumentation. However, the advantage of using such sensors for in-situ monitoring is often offset by the need of partially dismantling the network at the time of periodic network nodes calibration. As a result, new reference standards suitable for automatic and in-situ calibration of such sensors networks are needed in order to reduce the calibration cost, the inherent inefficiency and the logistic problems of a laboratory calibration, further exploiting the communication capabilities of a WSN. This work discusses the development of a wireless reference node (WRN) for the measuring of environment quantity such as air temperature (T) and relative humidity (RH). The module was developed for accurate measurements of additional environmentrelated quantities whose principle is based on a capacitive sensing mechanism (e.g. pressure, air-flow, moisture, etc…). The WRN performance was investigated in the temperature range from 0 °C to 40 °C and in the relative humidity range from 10 %rh to about 90 %rh for its potential use as a transfer standard for automatic in-situ calibrations. Some of novelties here reported were patented and are now available to upgrade a basic WSN with an automatic in-situ calibration capability

Validation of phosphor thermometry for industrial surface temperature measurements

Surface temperature measurements are required by the aerospace and automotive industries to guarantee high-quality products and optimize production processes. Accurate and reliable measurement of surface temperature is very challenging in an industrial environment. Surface contact probes are widely used but poorly characterized, while non-contact infrared thermometry is severely hampered by the unknown emissivity of the surface and by problems caused by stray radiation from the background. An alternative approach to the above techniques is phosphor thermometry, used here in a hybrid contact/non-contact approach. In this work, the development of a lifetime-based phosphor thermometer, its application to industrial surface temperature measurement and its validation are reported in a metrologically sound manner. The phosphor thermometer was initially calibrated by contact on a reference calibrator system at the Istituto Nazionale di Ricerca Metrologica to provide SI traceability to the measurements at the industrial level; the system was later validated by exploiting a metal phase-change method. The robustness of the approach against a strong radiative background was also investigated. A comprehensive uncertainty analysis was carried out, resulting in an expanded uncertainty (k  =  2) lower than 1.4 °C over the temperature range from the ambient to 450 °C. The phosphor-based thermometer was then tested at industrial manufacturing premises to measure the surface temperature of aluminium alloy billets during the pre-heating phase before forging. The phosphor-based approach was compared with radiation and contact thermometry in both static and dynamic measurement conditions. The experimental results proved that phosphor thermometry, besides being a valid alternative to conventional techniques, may offer better performance in an industrial setting

Whispering gallery mode thermometry

This paper presents a state-of-the-art whispering gallery mode (WGM) thermometer system, which could replace platinum resistance thermometers currently used in many industrial applications, thus overcoming some of their well-known limitations and their potential for providing lower measurement uncertainty. The temperature-sensing element is a sapphire-crystal-based whispering gallery mode resonator with the main resonant modes between 10 GHz and 20 GHz. In particular, it was found that the WGM around 13.6 GHz maximizes measurement performance, affording sub-millikelvin resolution and temperature stability of better than 1 mK at 0 °C. The thermometer system was made portable and low-cost by developing an ad hoc interrogation system (hardware and software) able to achieve an accuracy in the order of a few parts in 109 in the determination of resonance frequencies. Herein we report the experimental assessment of the measurement stability, repeatability and resolution, and the calibration of the thermometer in the temperature range from −74 °C to 85 °C. The combined standard uncertainty for a single temperature calibration point is found to be within 5 mK (i.e., comparable with state-of-the-art for industrial thermometry), and is mainly due to the employed calibration setup. The uncertainty contribution of the WGM thermometer alone is within a millikelvin

Assuring measurement traceability to ATE systems for MEMS temperature sensors testing and calibration

In the framework of an EMPIR joint research project (MET4FoF - Metrology for Factory of Future), a facility is being developed to provide in-situ measurement traceability to next-generation of Automated Test Equipment (ATE) systems used in MEMS temperature sensors testing and calibration. The above measurement traceability concepts are demonstrated in a testbed developed by SPEA in collaboration with INRIM and IPQ. The experimental work comprises both the factory-side implementation and the laboratory-side developments of a special calibration facility, to cover the temperature range between approximately -60 °C and 200 °C. On the factory side, SPEA develops a novel ATE prototype system, based on the concepts of good metrology practice, with the possibility to calibrate/validate in-situ the electronic circuitry and the on-board reference temperature sensors. The novel ATE prototype implements: • An improved temperature control system, with a new design of heaters, temperature sensors and MEMS temperature conditioning features. • A CPU software/firmware improvements to store sensors’ calibration coefficients and allow a “one-touch calibration” feature (i.e. a fully automatic process able to perform a comparison calibration of the ATE on-board reference temperature sensors). • An assessment of thermal conditions (homogeneity, heat losses, boundary effects) to estimate temperature calibration uncertainty. • A so-called “reference fixture”, i.e. an instrumented sensor socket equipped with a network of laboratory-calibrated reference sensors. On the laboratory side, INRIM develops calibration facilities and measurements methods to provide traceable temperature and electrical measurements to the above ATE systems. A custom equipment is developed to accommodate the sensors belonging to the reference fixture in order to calibrate them by comparison in a thermostatic bath. IPQ deals with the numerical simulation, by means of a 3D model of the temperature uniformity of the thermal chuck i.e. the ATE component providing the thermal stimulus to the MEMS under test. The simulation data will be used to help the SPEA hardware designer to improve the type, number and position of reference sensors on the thermal chuck to provide a more reliable and metrologically characterized thermal stimulus. The final paper will describe how an ATE machine works and in which parts it consists and how it is modified to reach the final goal. Furthermore, simulation data will be cross-compared with experimental data coming from metrological characterization before and after the ATE improvements in order to demonstrate their effectiveness. Also the method to assure traceability in large-scale temperature MEMS testing will be detailed and an example of application will be reported. Finally, it is expected that the outcome of this work will impact the quality and reliability of the MEMS sensors largely used in consumer electronics and will extend the calibration capability provided by INRIM to such an expanding industrial sector

Water vapor concentration measurements in high purity gases by means of comb assisted cavity ring down spectroscopy

In manufacturing processes of semiconductor industry accurate detection and monitoring of water vapor concentration in trace amount is of great importance. The ability to perform reliable measurements in ultrapure gases, with a wide dynamic range and low uncertainty, can have a substantial impact on product quality and process performances. Here, we report on the development of a second-generation comb-assisted cavity ring-down spectrometer and present H2O mole fraction measurements in high-purity N2 gas. Based on the use of a pair of phase-locked lasers and referenced to an optical frequency comb synthesizer, the spectrometer allowed to record high-quality absorption spectra in coincidence with the 32,2 → 22,1 H2O transition at 1.3946 μm. Retrieval of water mole fractions, at levels as low as 380 part per billion, was accomplished through a careful spectra analysis procedure based on the use of refined line shape models which include speed-dependent effects. Measurements were performed with a statistical reproducibility of 5 parts per billion, for an integration time of about 0.2 s. The noise equivalent and minimum detectable absorption coefficients were found to be 3.1 × 10−11 cm−1/ √ and 6.5 × 10−12 cm−1 , respectively. This latter allowed for a minimum detectable water mole fraction (limit of detection) of 160 parts per trillion. Finally, the main sources of systematic uncertainty have been discussed and quantified.This work was done within the project PROMETH2O (EMPIR 20IND06), which received funding from the EMPIR programme cofinanced by the Participating States and from the European Union's Horizon 2020 research and innovation programme

Expansion of European research capabilities in humidity measurement

Humidity is among the most important measured parameters related to HVAC applications, the storage of food products, industrial and medical gases, textile, paper and many other products requiring humidity measurement and control within certain limits. Humidity measurement techniques are diverse and each presents different challenges for use and calibration for a range of pressures and gases. Over the past few years, the development of humidity sensors and apparatus has matured to a level where traceable calibration is beneficial to all industries in which humidity and moisture measurement and control are important

Towards improved humidity measurements at high temperatures and transient conditions

Humidity is a key parameter in controlling drying processes and ambient conditions in many industrial manufacturing, storage and test applications. Air humidity is routinely measured at temperatures above 100 °C and at conditions that are often challenging due to temporal and local variations. Calibrations of humidity sensors do not provide appropriate representativeness of measurement conditions because they are limited to temperatures below 100 °C and static conditions. A European metrology research project HIT (“Metrology for Humidity at High Temperatures and Transient conditions”) is developing improved humidity measurement and calibration techniques to temperatures up to 180 °C and non-static conditions. This paper summaries developments of the project: calibration and test facilities for industrial hygrometers, studies on humidity control in specific microbial transient processes and a new measurement approach for water activity measurements