Calibration of Thermometers Avoiding the Use of Mercury

**校准温度计避免使用水银**高精度实验室温度计需要使用“定点电池”校准；细胞被用来校准温度计以达到最高的精度，细胞依赖于纯物质的相变。在较高的温度下，纯金属锭被包裹在一个可以放置温度计的组件中。当金属锭熔化或冻结时，温度保持恒定。这些固定点在1990年国际温标（ITS-90）中规定，这是国际公认的近似SI温度单位开尔文。最常用的低温定点电池使用纯汞，其参考温度为-38.8344°C。使用汞是一种非常方便和历史悠久的（也是唯一）校准用于实现和传播ITS-90\的标准铂电阻温度计（sprt）的方法。然而，汞是一种有害物质，它现在被禁止在电子设备中使用。科学界非常担心汞可能很快就会被禁止用于校准目的；运输汞已经非常困难和有问题，因为电池既需要为新安装提供，又需要移动以重新校准。科学家们正在研究替代品，包括二氧化碳（CO2, -56.6°C）和六氟化硫（SF6, -49.6°C）。Isotech开发了一种二氧化碳（CO2）固定点电池，其工作温度约为-56.6°C。我们无法实现三相点或以足够低的不确定度测量温度，不是因为缺乏设备或商业服务，而是因为需要新的实现和测量技术来实现这个新的校准点，无论是热性能还是确定CO2\的纯度。我们相信，通过利用NMI社区（即NPL）的经验和专业知识，我们可以将二氧化碳电池商业化，这将解决或减少使用有害汞的需求，使测量社区放心并消除汞对环境的担忧，并使Isotech在国际市场上具有显着的商业优势。

**Calibration of Thermometers Avoiding the Use of Mercury**High-accuracy laboratory thermometers need to be calibrated by using 'fixed point cells'; cells are used to calibrate thermometers to the highest accuracy, and cells rely on the phase change of a pure substance. At higher temperatures, pure metal ingots are encased in an assembly into which a thermometer can be placed. As the metal ingot melts or freezes the temperature remains constant. These fixed points are specified in the International Temperature Scale of 1990 (ITS-90), the internationally agreed approximation to the SI unit of temperature, the kelvin.The most used low-temperature fixed point cell uses pure mercury, which provides a reference of -38.8344°C. Using mercury is a very convenient and time-honoured (and only) way of calibrating the standard platinum resistance thermometers (SPRTs) used for realising and disseminating the ITS-90\.However, mercury is a hazardous substance, and its use is now prohibited in electronic equipment. The scientific community has great concern that mercury could soon be banned for calibration purposes; it is already very difficult and problematic to ship mercury as cells need to be both supplied for new installation, and moved for re-calibration.Scientists are researching alternatives, including carbon dioxide (CO2, -56.6 °C) and sulfur hexafluoride (SF6, -49.6 °C).Isotech has developed a carbon dioxide (CO2) fixed point cell, it operates at approximately -56.6 °C. We are unable to realise the triple point or to measure the temperature with a sufficiently low uncertainty, not for lack of equipment or commercial service, but for the need of novel realisation and measurement techniques for this new calibration point, both for the thermal performance and for determining the purity of the CO2\.We believe that by leveraging the experience and expertise of the NMI community (i.e. NPL) we can commercialise the CO2 cell, which would solve or reduce the need to use hazardous mercury, reassuring the measurement community and eliminating the environmental concerns over mercury, and giving Isotech a significant commercial advantage in the international marketplace.