ABSTRACT
Manometric thermometers are dened in this handbook as those thermometers that make use of the pressure of a gaseous medium as the physical quantity to obtain temperature. Very seldom are they available from commercial sources; for example, the temperature control of a home freezer is oen of this kind. Consequently, instead of simply buying one, every user must build his or her own when this type thermometer is needed. ey can be a quite useful choice since, in the era of electronic devices and sensors, it is still possible to make a totally nonelectronic thermometer, though of modest precision, which in addition keeps its calibration indenitely, as long as the quantity of substance sealed in it remains unchanged. e range of temperatures that can be covered by this kind of thermometer depends on the principle and on the substance used. When the thermodynamic equilibrium between the condensed phase of a substance (either liquid or solid) and its vapor is used, one has a “vapor-pressure thermometer,” and the temperature range spanned by each substance is generally narrow. In addition, only substances that are gaseous at room temperature (i.e., condensed at temperatures lower than 0 °C) are normally used, conning the working range to below room temperature; however, some substances that are liquid at room temperature and have a high vapor pressure (i.e., which easily evaporate) have been used, but do not result in a sizable extension of the working range much above room temperature. A special case of vapor pressure being used at high temperature is the device called a “heat pipe,” which is not used as a thermometer, but instead as an accurate thermostat [1]; using sodium, the working range is pushed up to ∼1100 °C. When a pure substance is used only in its gaseous state, one has a “gas thermometer,” whose temperature range can be very wide, especially for moderate accuracy, depending mainly on the manometer; on the other hand, its fabrication is somewhat more complex and its use normally much less straightforward.
