Calibration barometers

The corrections above do not apply to aneroid barometers. These instruments should be calibrated at regular intervals by checking them against a corrected mercurial barometer. 

For records on weather maps, meteorologists customarily correct barometer readings to sea level, and some barometers may be calibrated accordingly. Such instruments are not suitable for laboratory use where true pressure under standard conditions is required. Scale corrections should be specified in the maker s instructions with the instrument, and are also indicated by the lack of correspondence between a gauge mark usually placed exactly 76.2 cm from the zero point and the 76.2-cm scale graduation. 

Stock solution. The concentration of the stock solution was determined by the sodium iodate-thiosulfate titration method. For each determination, a 100.0-ml solution was prepared and placed in a vessel connected to a manometer for measuring the pressure. The vessel was sealed after insertion of a measured piece of catalase-immobilized CoFoam. The reaction of catalase with peroxide produces O2, and an increase in pressure indicates a degradation of the peroxide. Thus, a change in pressure in the vessel is a measure of the reaction rate. Since it is sufficient to show differences in test samples, the ideal gas law was used to convert the pressure into mass. The barometer was calibrated with a gauge traceable to National Institutes of Standards and Technology (NIST) standards. 

The third calculation is the conversion of pressure units from pounds per square inch read from a guage (psig) to pounds per square inch absolute (psia). Strictly speaking, the value of barometric pressure in psi read from a barometer at the time the pressure gauge was calibrated should be added to psig to get psia. At sea level, a value of 14.7 psi is usually sufficiently accurate. 

In physics, the use of calibration hierarchies is well established and is used in any laboratory, e.g. for balances, volumetric equipment, spectrometer wavelengths, cuvette light path lengths, thermometers, barometers and clocks. 

Steam bath calibration for the liquid-steam point of H20 is not easy for many labs to use because of its expense, and the equipment is difficult to use. In addition, the user needs to account for atmospheric pressure variations and the effects of local variations of gravity on the barometer. Fortunately, the ice-point calibration is easy to set up and use. 

Pressure Measurements The term mm Hg used with respect to pressure within an apparatus, or atmospheric pressure, refers to the use of a suitable manometer or barometer calibrated in terms of the pressure exerted by a column of mercury of the stated height. 

Whatever style of notebook is used, the principle is the same Record all data directly in your notebook. Data may be copied into tlie notebook from a partner s notebook in those cases where it is clearly impossible for both partners to record data at the same time. Even then, a carbon copy or a photocopy of the original pages is better, since it avoids copying errors and saves time. In particular, do not use odd scraps of paper to record such incidental data as weights, barometer readings, and temperatures with the idea of copying them into the notebook at a later time. If anything must be copied from another source (calibration chart, reference book, etc.), identify it with an appropriate reference. 

If a thermocouple or PRT was used, convert its readings to temperatures with an appropriate cahbration eqrration. It may be wise to check the calibration by measuring the bath temperature at atmospheric pressure. Calculate this bath temperature from Eq. (12) using the pressure determined with a barometer. If necessary, one can then apply a constant additive correction to all PRT resistance or thermocouple emf readings. 

Mercury Manometers. A U-tube manometer filled with mercury is simple to construct, requires no calibration, and operates over a wide pressure range. It is now less frequently used due to concerns about safety hazards associated with mercury (see Appendix C) and its slow visual readout. However, it is a historically important device and it is directly related to barometers, which are discussed in Chapter XIX. 

Ballhaus C., Berry R. F., and Green D. H. (1991) High pressure experimental calibration of the olivine-orthopyroxene-spinel oxygen barometer implications for the oxidation state of the upper mantle. Contrib. Mineral. Petrol. 107, 27-40. 

Nimis P. and Taylor W. R. (2000) Single clinopyroxene thermobarometry for garnet peridotites Part 1. Calibration and testing of a Cr-in-cpx barometer and enstatite-in-cpx thermometer. Contrib. Mineral. Petrol. 139, 541-554. 

Pressure-measuring devices may be divided into two groups those which measure the pressure directly and can be calibrated without reference to another intrument and those which involve some other physical measurement which will be related to the pressure. Of the former type, the barometer, manometer, and McLeod gauge are the most common. 

The mode of calibration is determined by the design of the instrument. Most instruments contain a barometer or a transducer responsive to P(Amb) so that barometric pressure is always known to the microprocessor. With such instruments, only a keyboard entry of the fractional composition of O2 and CO2 in low and high calibrator gas mixtures needs to be made. Today, most analyzers auto-calibrate without the necessity for user input. The microprocessor will calculate the values for PO2 and PCO2 (according to Dalton s law) for gases saturated with water vapor at 37 °C. 

It is advisable to have barometers checked occasionally against a standard instrument so that the corrections to be applied at various readings may be known. Aneroid barographs should be calibrated in the same way. These instruments — which generally have an accuracy of not more than 0-5 mm — are provided with charts running either for a day or a week. The charts should be fUed, in order that the atmospheric pressure at any time can be subsequently found. Aneroid barographs are as a rule compensated for errors due to temperature in the range of —40° to +40 °C by bimetallic strij).s. 

BAROMETER - Instrument for measuring atmospheric pressure. It may be calibrated in pounds per square inch, in inches of mercury in a column in millimeters or kPa. 

It is veiy important to understand the general aspects of gas pressure, its measurements, and calibrations. Pressure is force exerted over imit area. The unit of pressure is pascal (Pa) which is equivalent to kg/(m.s ). In chemistry, we usually use a mercury-based barometer to measure the pressure. The unit is millimeter of mercury (mmHg). This is the same as the unit torr. Another unit commonly used to denote pressure is atmosphere (atm). You should be able to convert these units back and forth as required. 

The apparatus used in this study consisted of a vacuum chamber containing a spherical cryosurface and an independent gas addition system. The gas addition system, shown in Fig, 1, comprised a surge tank, a barometer for measuring the upstream gas pressure, and a series of five calibrated standard leaks, with individual valves, arranged in parallel, permitting individual use of each leak or any combination of leaks. The entire gas addition system has a separate pumping station. 

This work anticipated that published by Faraday. Cavendish s paper on the Royal Society s instruments dealt not only with thermometers but also with the effect of capillarity on the height of mercury in a barometer tube and the correction for temperature, the rain-gauge, hygrometer, dipping needle, and variation compass. It contains careful observations on the construction and calibration of mercury thermometers. Lord Charles Cavendish had previously described what is essentially a Beckmann thermometer with a variable zero. Cavendish constructed an ingenious registering (maximum and minimum) thermometer, which is now in the Royal Institution. ... 

The standard in sphygmomanometers uses a column of mercury, exactly as a mercury barometer does. It requires a separate stethoscope and a trained ear for proper operation. Another type of device is called an aneroid sphygmomanometer, which uses an analog gauge that is calibrated against a mercury column. 

A6.6.2.1 For pressures between atmospheric and 13.3 kPa (100 mm Hg), vacuum calibration is ba on an evacuated mercury barometer or manometer. For pressures below 13.3 kPa, the McLeod gage is the primary standard and must be carefully calibrated. Seconda gages should be checked at least weekly in routine service or before each use in irregular service... 

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