Vacuum Radiance-Temperature Standard Facility for Infrared Remote Sensing at NIM

As infrared remote sensors are very important parts of Earth observation satellites, they must be calibrated based on the radiance temperature of a blackbody in a vacuum chamber prior to launch. The uncertainty of such temperature is thus an essential component of the sensors’ uncertainty. This paper describes the vacuum radiance-temperature standard facility (VRTSF) at the National Institute of Metrology of China, which will serve to calibrate infrared remote sensors on Chinese meteorological satellites. The VRTSF can be used to calibrate vacuum blackbody radiance temperature, including those used to calibrate infrared remote sensors. The components of the VRTSF are described in this paper, including the VMTBB, the LNBB, the FTIR spectrometer, the reduced-background optical system, the vacuum chamber used to calibrate customers’ blackbody, the vacuum-pumping system and the liquid-nitrogen-support system. The experimental methods and results are expounded. The uncertainty of the radiance temperature of VMTBB is 0.026 °C at 30 °C over 10 μm.     

Radiation Thermometry Based on Photonic Crystal Fiber

Fiber-coupled radiometry allows for the radiometric measurement of high temperatures in environments where there is no line of sight to the target. However, transmission through conventional silica optical fibers degrades rapidly at elevated temperatures, and exotic fibers??such as sapphire fibers??typically cannot be bent. As part of a project to investigate the performance of solid oxide fuel cells, the feasibility of using an alternative fiber, solid-core silica photonic crystal fiber (PCF), was tested. The test system used an Inconel blackbody as a source, and a detection system based on an InGaAs array spectrometer with a wavelength range of 907 nm to 1681 nm. The temperature was determined from the spectrometer signal at particular wavelengths using the Planck relationship. Two tests were performed: (1) long-term high temperature soak tests to measure the drift and noise in thermal radiation levels, in which spectra are sequentially recorded over a long period of time with the blackbody cavity at a constant temperature and (2) temperature dependence tests, whereby thermal radiation spectra are recorded with the blackbody cavity at several temperatures. At 934 °C, the transmission of the PCF decreased at a rate of 0.078 % per hour corresponding to a temperature error of ?0.12 °C per hour. The transmission of conventional silica fiber decreased at a rate of 0.5 % per hour corresponding to a temperature error of ?0.8 °C per hour. While the PCF represents a significant improvement over conventional fiber, it is still not good enough for most practical purposes. At 600 °C there was no observable decline in transmission and there may be applications for PCF in that regime.     

Thermal Characteristics of a Sealed Glass-Water Heat Pipe from 0?��C to 60?��C

Investigations into the thermal characteristics of glass-water heat pipes from 0 °C to 60 °C were carried out at the National Institute of Metrology (NIM), China. In this paper, studies on a glass-water heat pipe with four thermometer wells are described. The experimental results indicated that the temperature stability and uniformity of the thermometer well of the glass-water heat pipes are within several tenths of a millikelvin when the heat pipes are immersed in a constant-temperature liquid bath, since they have a highly effective thermal conductivity. They are able to maintain a constant temperature by the absorption or liberation of the latent heat of evaporation to attenuate temperature fluctuations of the surroundings. Also, above 0 °C to 30 °C, the temperature stability of the thermometer well of the glass-water heat pipe is better than 0.1 mK for approximately 16 h. The maximum temperature differences among the thermometer wells are less than 5.5 mK when the water heat pipes operate in the range from 0 °C to 60 °C. Therefore, water heat pipes are very promising to improve the performance of liquid baths and to accurately calibrate thermometers by comparison.     

Refractive index and strain sensor made of S-tapered photonic crystal fiber

An experimental investigation on an S-tapered photonic crystal fiber interferometer is presented in this paper. The sensor exhibits highly surrounding refractive index sensitive, which is 4.7 × 10^?3 RIU (refractive index unit) in 1.33–1.39 and 1.45 × 10^?3 RIU in 1.39–1.44 commensurable with general sensors. Attribute to the S-shape’s distortion, red shifts are measured in axial strain test. In addition, insensitivity (4.3 pm/°C) in low temperature and sensitivity (22.4 pm/°C) in high temperature are confirmed by experiments. These properties combined with a simple fabrication process and a durable structure.     

Experiences in Calibrating Industrial Platinum Resistance Sensors Between − 196 °C and 80 °C

Recently, a requirement arose to provide sensors for measuring the temperature of a substantial reference blackbody cavity to operate in vacuum over a temperature range from ? 100 °C to 80 °C (~?170 K to ~?350 K), with an additional capability to operate at ~? 170 °C (~?100 K) as a point of near-zero radiance. Several 100 Ω industrial platinum resistance sensors (Pt100) are required for control purposes in order to establish the temperature uniformity of the blackbody structure and its surrounding aluminum-alloy isothermal shield. These sensors should remain stable within the uncertainties of 0.03 °C (k?=?3) ideally for 20 years. This paper discusses the testing and calibration of two types of industrial Pt100 resistors, including checking the interchangeability of sensors from a given batch, and the methods of interpolation over the temperature range. It is concluded that the sensors can meet the requirements provided that they have been individually tested, and that there is a degree of duplication of sensors so that long-term changes can be detected. The calibration data could be fitted by cubic or quartic equations expressing temperature as a function of resistance (or resistance ratio), this being simpler than the ITS-90 formulation and more convenient than using the (technically obsolete) Callendar–Van Dusen equation.     

Construction and Characterization of a Large Aperture Blackbody for Infrared Radiometer Calibration

A large aperture blackbody (LABB) with a diameter of 1 m has been successfully constructed for calibrating radiation thermometers and infrared radiometers with a wide field of view in the temperature range between 10 °C and 90 °C. The blackbody is a 1 m long cylindro-conical cavity with a diameter of 1.1 m. Its conical bottom has an apex angle of 120°. To achieve good temperature stability and uniformity, the cavity is integrated to a water-bath to which the pressurized water is supplied from a reservoir. To reduce the convection heat loss from the cavity to the ambient, the cavity is purged of the dried air that passes through a coiled tube immersed in the reservoir. For an uncertainty evaluation of the LABB, its temperature stability was measured by using a reference radiation thermometer (RRT) and a platinum resistance thermometer (PRT), and its radiance temperature distributions on the aperture plane were measured by using a thermal camera. Measuring the spectral emissivity of the coating material, the effective emissivity of the blackbody was calculated to be 0.9955 from 1 ??m to 15 ??m. The expanded uncertainty of the radiance temperature scale was evaluated based on the PRT readings, which vary from 0.3 °C to 0.5 °C (k = 2) in the temperature range. The temperature scale is validated by comparing with the RRT of which the temperature scale is realized by a multiple fixed-point calibration.     

Calibration of Radiation Thermometers and Blackbodies in the Temperature Range from 160 ��C to 420 ��C

The NMIJ has established a new calibration facility consisting of a 1.6??m radiation thermometer and three fixed-point blackbodies of indium (156.5985 °C), tin (231.928 °C), and zinc (419.527 °C) in the temperature range from 160 °C to 420 °C. The expanded uncertainties (k = 2) of the fixed-point blackbodies are estimated to be 28 mK for the In point, 22 mK for the Sn point, and 32 mK for the Zn point. The expanded uncertainties in the temperature scale of the 1.6??m radiation thermometer are estimated to be 40 mK to 77 mK. When this standard is used to calibrate devices under test to be used in industry, uncertainties (k = 2) of 61 mK for the In point, 67 mK for the Sn point, and 99 mK for the Zn point, 91 mK to 136 mK for a 1.6??m radiation thermometer, and 73 mK to 116 mK for a variable-temperature blackbody can be achieved.     

A Cryostat for Automated mK-Level Thermometer Calibrations from ?202??��C to 250?��C

The National Measurement Institute of Australia (NMIA) has developed a vacuum cryostat capable of calibrating precision electronic thermometers with a transfer error less than 2 mK over the range from ?202 °C to 250 °C. The calibration of precision temperature measurement probes such as platinum resistance thermometers is usually performed in circulated fluid baths to achieve mK-level calibration uncertainties, and requires the use of several baths to cover the commonly used range of ?80 °C to 250°C. Below ?80 °C, dry-well systems cooled by liquid nitrogen are available down to ?196 °C, but achieve poor uniformity and stability. The increased use of cryogenic preservation in the biomedical area has seen an increase in demand for precision calibration of electronic thermometer systems, in particular, down to a few degrees below the boiling point of nitrogen (?196 °C). This has prompted NMIA to develop a new design of a dry-well calibrator, based around a 380 mm long, 50 mm diameter, oxygen-free copper block insulated by gold-plated radiation and guard shields. Temperatures down to ?202 °C are achieved by controlling the flow of liquid nitrogen through a restricting orifice into an evacuated heat exchanger. Computer control of the nitrogen flow and of several immersion heaters achieve a temperature stability of a few mK at all temperatures over the operational range, requiring typically 60 min to equilibrate at each new setpoint. Radiative transfer limits operation to 250 °C where the uniformity is 0.5 mK · cm^?1 (and becoming negligible at lower temperatures). A significant design innovation is the thermometer entry region, which has a purge system to keep the wells free of condensed moisture or atmospheric gases without the need for a seal. As the block is only 50 mm from the face of the cryostat, thermometers as short as 250 mm can be calibrated. The system is now in regular use at NMIA providing fully automated calibrations of precison temperature measurement systems without the need to use multiple temperature enclosures.     

Construction of Sodium Heat-Pipe Furnaces and the Isothermal Characteristics of the Furnaces

Due to an excellent temperature flattening ability, annular sodium heat pipes operating from 500 °C to 1200 °C have been widely used as liners for isothermal furnaces to provide uniform and stable temperature zones. In order to develop the capabilities to fabricate liquid-metal heat pipes, an apparatus for fabricating sodium heat pipes was set up at the National Institute of Metrology (NIM), China. In this paper, the newly developed fabrication apparatus, the detailed procedures for manufacturing sodium heat pipes, the sodium heat pipes, the constructed furnaces for realizing the aluminum freezing point, and their isothermal characteristics are described. The experimental results showed that the biggest temperature differences within 150 mm from the bottom of the thermometer well in an aluminum point cell placed in the sodium heat-pipe furnaces were better than 15 mK, when the temperatures of the furnaces were controlled at approximately 657 °C.     

Failure analysis of a high-temperature thermocouple

A solid oxide fuel cell unit operates at high temperatures of 700 to 800°C. The operation of the unit is controlled by a set of instrumentation including sensors, thermocouples, and voltage leads. Two S-thermocouples were inserted in the after-burner where temperature is constantly at 1000°C. During operation of one prototype unit and after 1000 h, the thermocouples started to give erratic readings and led to complete shutdown of the unit. Analysis of the thermocouples revealed a series of events may have occurred due to stress induced by the design, materials and operating conditions, contamination during manufacturing, or a reducing environment caused by sheathing. The specification from S-type to B-type may remove the risk of reoccurrence. A design change in platinum burner thermocouples to ensure an oxygen-rich environment for the platinum was also recommended.     

光纤燃油液位传感器研究现状

液位测量传感器是飞机燃油测量系统中的重要组成部分。光纤燃油液位传感器因其本质安全的特性而在飞机燃油液位测量领域备受关注。根据被测对象对光的调制形式不同,将光纤液位传感器分为光强调制型和波长调制型两类,总结各种传感器的原理和应用现状,讨论不同类型传感器的性能和优缺点,并对今后的发展方向做出展望。     

Performance evaluation of a stack cooling system using CO2 air conditioner in fuel cell vehicles

A relation between the heat release from a fuel cell stack and an air conditioning system's performance was investigated. The air conditioning system installed in a fuel cell vehicle can be used for stack cooling when additional stack heat release is required over a fixed radiator capacity during high vehicle power generation. This study investigated the performance of a stack cooling system using CO₂ air conditioner at various operating conditions. Also, the heat releasing effectiveness and mutual interference were analyzed and compared with those for the conventional radiator cooling system with/without cabin cooling. When the radiator coolant inlet temperature and flow rate were 65 °C and 80 L/min, respectively, for the outdoor air inlet speed of 5 m/s, the heat release of the stack cooling system with the aid of CO₂ air conditioner increased up to 36% more than that of the conventional radiator cooling system with cabin cooling. Furthermore, this increased by 7% versus the case without cabin cooling.     

An Investigation of the Relation Between Contact Thermometry and Dew-Point Temperature Realization

Precision optical dew-point hygrometers are the most commonly used transfer standards for the comparison of dew-point temperature realizations at National Metrology Institutes (NMIs) and for disseminating traceability to calibration laboratories. These instruments have been shown to be highly reproducible when properly used. In order to obtain the best performance, the resistance of the platinum resistance thermometer (PRT) embedded in the mirror is usually measured with an external, traceable resistance bridge or digital multimeter. The relation between the conventional calibration of miniature PRTs, prior to their assembly in the mirrors of state-of-the-art optical dew-point hygrometers and their subsequent calibration as dew-point temperature measurement devices, has been investigated. Standard humidity generators of three NMIs were used to calibrate hygrometers of different designs, covering the dew-point temperature range from ?75 °C to + 95 °C. The results span more than a decade, during which time successive improvements and modifications were implemented by the manufacturer. The findings are presented and discussed in the context of enabling the optimum use of these transfer standards and as a basis for determining contributions to the uncertainty in their calibration.     

红外空芯光纤辐射温度计的研制及应用

为了对冲击发电机的轴套温度进行监测,设计并研制了一种新型的红外光纤辐射温度计.温度计主要由红外空芯玻璃光纤、红外探测器、放大电路及80C552单片机组成.在分析各部分实现功能的基础上,重点研究了环境温度变化对探测器的影响,并实现了数学建模.温度计的工作波长是8~14μm,测量温度范围是60~400℃,测试环境温度范围是25~60℃.利用可精确控温的实物标定炉和环境模拟箱对温度计进行了标定,测量误差小于2%.经过几个月的在线监测,取得了较好的测量结果.     

Research on H500-Type High-Precision Vacuum Blackbody as a Calibration Standard for Infrared Remote Sensing

Based on the calibration requirements of vacuum low background aerospace infrared remote sensing radiance temperature, a high-precision vacuum blackbody (H500 type) is developed for the temperature range from ??93 °C to +?220 °C at the National Institute of Metrology, China. In this paper, the structure and the temperature control system of H500 are introduced, and its performance, such as heating rate and stabilization of temperature control, is tested under the vacuum and low-background condition (liquid-nitrogen-cooled shroud). At room temperature and atmospheric environment, the major technical parameters of this blackbody, such as emissivity and uniformity, are measured. The measurement principle of blackbody emissivity is based on the control of surrounding radiation. Temperature uniformity at the cavity bottom is measured using a standard infrared radiation thermometer. When the heating rate is 1 °C min^?1, the time required for the temperature to stabilize is less than 50 min, and within 10 min, the variation in temperature is less than 0.01 °C. The emissivity value of the blackbody is higher than 0.996. Temperature uniformity at the bottom of the blackbody cavity is less than 0.03 °C. The uncertainty is less than 0.1 °C (k?=?2) over the temperature range from ??93 °C to +?67 °C.     

Thermal effect on the output transmission of single-core fiber Comb filter

We propose and experimentally demonstrate switchable and tunable transmission characteristics of a single-core comb filter based on thermal operation. Its temperature characteristics are investigated to reveal a shift in the peak wavelength position from 0.15 to 0.41 nm/°C and a tunable range of wavelength spacing of 1.18–1.38 nm for maximum and minimum effective lengths, respectively. This configuration provides the unique advantages of an all-fiber structure, tunable wavelength spacing, switchable spectral peaks, independent tuning of the center wavelength and wavelength spacing of the spectral peaks, and low polarization sensitivity. It is relatively simple to fabricate and is expected to have applications in temperature fiber optic sensors and multiwavelength fiber laser sources.     

In situ growth of Prussian blue nanocubes on polypyrrole nanoparticles: facile synthesis,characterization and their application as fiber optic gas sensor

Polypyrrole (PPy) and polypyrrole/Prussian blue (PPy–PB) nanocomposite-based fiber optic gas sensors are developed for gas sensing application. Prussian blue (PB) nanocubes are successfully grown on polypyrrole (PPy) nanoparticles by in situ oxidative polymerization method to obtain PPy–PB nanocomposite. PPy and PPy–PB are evaluated based on structural, morphological and electrical properties. The characteristic peaks present in the FTIR spectra of pure PPy and PB nanoparticles are also present in the FTIR spectrum of PPy–PB nanocomposite with small shifts in the absorption maximum. The XRD pattern reveals the semicrystalline structure of PPy–PB nanocomposite with an average crystallite size of 22 nm, and the morphology (FESEM) shows the formation of PB nanocubes over PPy matrix. AC conductivity measurements show slight improvement in the conductivity value of PPy–PB in comparison with PPy. Dielectric studies in the frequency range of 50 Hz–5 MHz reveal that PPy–PB nanocomposite is a high-k dielectric material. At 50 Hz, PPy–PB exhibits high dielectric constants of 1149 and 766 with low dielectric loss values of 9.9 and 4.6 at 150 and 120 °C, respectively. Further, their application as fiber optic gas sensors in sensing various gases is studied using fiber optic technique. The spectral response is studied for various concentrations (0–500 ppm) of ammonia, acetone and ethanol gases at room temperature. The study shows that the spectral intensity increases linearly with different concentrations of all gases. The clad-modified fiber optic sensor with PPy–PB nanocomposite exhibits enhanced sensitivity for ethanol than clad-modified fiber optic sensor with PPy nanoparticles. TGA studies reveal the high thermal stability of PPy–PB nanocomposite. Hence, PPy–PB-based fiber optic sensors can be used to sense toxic ethanol vapor not only at room temperature but also in a composite environment where a temperature variation is expected.     

Experimental study of temperature sensor for an ocean-going liquid hydrogen (LH2) carrier

The prototype temperature sensors for an ocean-going liquid hydrogen (LH₂) carrier were manufactured by way of trial. All of the sensors adopted Platinum 1000 (PT-1000) resistance thermometer elements. Various configurations of preproduction temperature sensors were tested in AIST’s LH₂ test facility. In the experiments, a PT-1000 resistance thermometer, calibrated at the National Metrology Institute of Japan at AIST, was used as the standard thermometer. The temperatures measured by the preproduction sensors were compared with the temperatures measured by the standard thermometer, and the measurement accuracy of the temperature sensors in LH₂ was investigated and discussed. It was confirmed that the measurement accuracies of the preproduction temperature sensors were within ±50 mK, which is the required measurement accuracy for a technical demonstration ocean-going LH₂ carrier.     

Improved High-Temperature Standard Platinum Resistance Thermometer

To prevent short circuits, to improve stability, and to raise the upper temperature limit to the freezing point of copper (1084.62 °C), the high-temperature standard platinum resistance thermometer (HTSPRT) was redesigned. The most important change was an improvement in the structure of the sensor support. The strip support was replaced by a new specially designed cross support. The structure and design of the new HTSPRT are briefly described in this article. The test results of a group of thermometers are presented. The test included long-term drifts of the thermometers at the triple point of water and freezing point of silver during a period of a few hundred hours operation at 1085 °C, the short-term stability of R (tpw) and W (Ag) in a period of 5 days, and thermal cycles between 22 °C and 1085 °C. The test results show that the thermometer performance is improved, and the new HTSPRT can operate up to the freezing point of copper.     

Calibration of Thermocouples and Infrared Radiation Thermometers by Comparison to Radiation Thermometry

The National Metrology Institute of Spain (CEM) has designed, characterized, and set-up its new system to calibrate thermocouples and infrared radiation thermometers up to 1600 °C by comparison to radiation thermometry. This system is based on a MoSi₂ three-zone furnace with a graphite blackbody comparator. Two interchangeable alumina tubes with different structures are used for thermocouples and radiation thermometer calibrations. The reference temperature of the calibration is determined by a standard radiation thermometer. Normally, this is used at CEM to disseminate the International Temperature Scale of 1990 (ITS-90) in the radiation range, and it refers to the Cu fixed point. Several noble metal thermocouples and infrared radiation thermometers with a central wavelength near 900 nm have been calibrated, and their uncertainty budgets have been obtained.