THERMOSTAT — the device for creation in the closed volume of a certain temperature and its maintenance on a fixed level. T. represents the capacity or the vessel of a cubic or cylindrical form which is carefully protected by thermal insulation from influence of the environment for the purpose of the smallest heat exchange with it. Emergence of T. it is connected with development of microbiology, is later than its steel to use at biochemical and other researches, at to-rykh it is necessary to maintain a long time constant temperature above or ambient temperatures are lower.
Distinguish T. for maintenance of high temperatures and T. for maintenance of low temperatures, or cryostats. Depending on the heat carrier T. happen liquid and sukhovozdushny. Liquid T. share on low-temperature, napr, spirit, in to-rykh temperature from — 60 to +10 °, water — temperature is maintained in range of 10 — 95 °, and high-temperature, napr, oil (t ° 100 — 300 °), salt or selitrovy (t ° 300 — 500 °). In sukhovozdushny T. thermostating to t ° 300 ° and more is provided. Originally the heat carrier was warmed up on naked flame, by hl now. obr. electricity. Constancy of temperature in T. it is provided with temperature regulators (dilatomichesky, bimetallic), the principle of action to-rykh is based on a difference of polar expansion of various metals or liquids at change of temperature, contact thermometers, electric resistance pyrometers, and also due to phase change (thawing of the ice, boiling of water and other phenomena) occurring at a certain temperature. T., in Krom maintenance of constant temperature is connected not with phase change, has built-in warming-up (thermoelements) or coolers. The heat carrier (or coolant), passing through the heater (or the refrigerator), gets necessary temperature, edges it is controlled by the temperature regulator or a contact thermometer if necessary including heating or cooling.
The main characteristics of the thermostats released in the USSR are provided in the table.
Modern T. have the automatic temperature recording controller of high precision, the heating or heating and cooling devices, and for more bystry alignment of temperature in T. — the device for vigorous hashing of the heat carrier. Camera T., as a rule, has double two-fold or single-door doors (fig. 1). Temperature in T., depending on its type, it is supported with an accuracy of ±0,1 — ±0,5 °. In ultrathermostats, to-rye have rather small volumes of the camera and the powerful, but low-inertia heater, temperature is maintained with a bigger accuracy due to vigorous hashing of the heat carrier and more perfect thermal control.
For a number of researches use submersible T. V them there is a heater, a temperature regulator and a mixer. These T. immerse in capacity with liquid, to-ruyu it is necessary to termostatirovat. For overseeing by the course of precipitation tests, coagulations, etc. use T. with transparent walls, and for filtering of hot solutions — T., in the working camera to-rogo the funnel and a decanter (fig. 2) are placed.
To special T. carry thermoses and vessels of the Dewar (see. Dewar vessel ), and also has a thermobath of TB-110, edge not side, as at all T., a door, and an upper cover that is convenient for placement of supports and brackets with test tubes, etc. the tanks filled with the studied drugs.
During the work with T. it is necessary to observe safety measures, as during the work with electric devices; the internal polished walls of T., having the maximum heatdeflecting wall to keep clean, preserving against corrosion and pollution.
Table. MAIN CHARACTERISTICS of THERMOSTATS
Bibliography: Koblov L. F. Methods and devices for clinical laboratory trials, M., 1979.
V. I. Belkevich.