【国外标准】 Standard Guide for Digital Contact Thermometers for Petroleum Products, Liquid Fuels, and Lubricant Testing

5.1 The information in the examples of this guide are intended to be a starting point for determining the appropriate DCT criteria for a test method that measures a temperature-dependent property of a product within the scope of Committee D02. The criteria examples noted in this guide are based on the liquid-in-glass (LiG) thermometer design components, which are the bulb length, immersion depth, precision of measurement, thermometer position, and so forth. The parameters such as sensor length, immersion depth, and sheath diameter are especially critical when measuring the temperature of small static samples. This is due in part to the difference in thermal conductivity of a LiG vs. a DCT, however other aspects of the devices can contribute to unequal results. For example a DCT that is suitable for use in a stirred constant temperature bath will likely result in measurement errors when used to measure the temperature of a small static sample. This difference can be a degree or more when the sample temperature differs from room temperature by 40 °C or more using a 7 mm probe. This error is due to the difference in thermal conductivity and specific heat value of a DCT and LiG thermometer, however other aspects of the two different devices can contribute unequal results. One way to counter this is by reducing DCT sheath diameter, insulating the sheath above the immersion level, and using a probe that has a small immersion depth as determined by Practice D7962. For more guidance on selecting an appropriate DCT, see Guide E2877.5.2 When replacing a LiG thermometer with a DCT noted in this guide and the test method does not list any DCT criteria, it is incumbent on the user to verify the suitability of the DCT they have selected. This can be done by comparing measurements made with the selected DCT to those of a LiG thermometer and following the test procedure. Comparative measurements are especially important when measuring the temperature of a small static sample where there is a large difference between sample and room temperature. Covering the DCT probe sheath except for the sensing portion with a glass, plastic, or tubing with a lower thermal conductivity can improve the agreement between LiG and DCT measurements.1.1 The intent of this guide is to suggest an initial configuration and provide guidance when establishing the appropriate criteria needed for a DCT to correctly measure the temperature in a laboratory test method for products within the scope of this committee. This guide includes examples of the approximate digital contact thermometer (DCT) criteria that was found suitable for measuring temperature in the test methods utilized by Committee D02.1.2 The values stated in SI units are to be regarded as standard. No other units of measurement are included in this standard.1.3 This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety, health, and environmental practices and determine the applicability of regulatory limitations prior to use.1.4 This international standard was developed in accordance with internationally recognized principles on standardization established in the Decision on Principles for the Development of International Standards, Guides and Recommendations issued by the World Trade Organization Technical Barriers to Trade (TBT) Committee.