ASTM D8164-19

5.1 The examples of DCT criteria noted in this guide are approximately those found to be suitable for replacing some of the noted liquid-in-glass thermometers with a DCT. The criteria 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 for sensor length, immersion depth, sheath diameter are especially critical when measuring the temperature of small static samples due to temperature probe thermal conductivity. A DCT that is suitable for use in a stirred constant temperature bath will likely result in measurement errors when used to measure small sample temperature. These 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 of a DCT and LiG thermometer. The most effective 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.