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Other units of pressure include: The bar (symbol: bar), defined as 100 kPa exactly. The atmosphere (symbol: atm), defined as 101.325 kPa exactly. These four pressure units are used in different settings. For example, the bar is used in meteorology to report atmospheric pressures. [7] The torr is used in high-vacuum physics and engineering. [8] [9]
Values are given in terms of temperature necessary to reach the specified pressure. Valid results within the quoted ranges from most equations are included in the table for comparison. A conversion factor is included into the original first coefficients of the equations to provide the pressure in pascals (CR2: 5.006, SMI: -0.875).
A special form of the Pirani gauge is the pulsed Pirani vacuum gauge where the sensor wire is not operated at a constant temperature, but is cyclically heated up to a certain temperature threshold by an increasing voltage ramp. When the threshold is reached, the heating voltage is switched off and the sensor cools down again.
calorie (International Table) cal IT: ≡ 4.1868 J = 4.1868 J: calorie (mean) cal mean: 1 ⁄ 100 of the energy required to warm one gram of air-free water from 0 °C to 100 °C at a pressure of 1 atm ≈ 4.190 02 J: calorie (thermochemical) cal th: ≡ 4.184 J = 4.184 J: Calorie (US; FDA) Cal ≡ 1 kcal = 1000 cal = 4184 J: calorie (3.98 °C ...
A Assuming an altitude of 194 metres above mean sea level (the worldwide median altitude of human habitation), an indoor temperature of 23 °C, a dewpoint of 9 °C (40.85% relative humidity), and 760 mmHg sea level–corrected barometric pressure (molar water vapor content = 1.16%). B Calculated values *Derived data by calculation.
The boiling point of water is the temperature at which the saturated vapor pressure equals the ambient pressure. Water supercooled below its normal freezing point has a higher vapor pressure than that of ice at the same temperature and is, thus, unstable. Calculations of the (saturation) vapor pressure of water are commonly used in meteorology.
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However, condensable gases, such as water vapour, ammonia, carbon dioxide, and pump-oil vapors may be in gaseous form in the low pressure of the vacuum chamber, but will condense when compressed by the McLeod gauge. The result is an erroneous reading, showing a pressure much lower than actually present.