Rotameter calibration

We are currently checking orifices prior to each survey with the direct reading rotameter, and washing them in isopropyl alcohol afterwards. Every six months, the calibration checks are performed with the wet test meter. As long as field checks and rotameter calibration checks agree with the bi-annual wet test meter calibration results, we feel the orifices are performing accurately. 

Each orifice constructed in the above manner was calibrated with a rotameter and manometer. The set-up used for orifice calibration is shown in Figure 3. The uncorrected flow readings were obtained from the rotameter calibration curve. The corrected flows were then calculated using the following equation ... 

Rotameter calibration data (flow rate versus rotameter reading) are as follows ... 

A rotameter calibration curve (flow rate versus float position) obtained using a liquid is mistakenly used to measure a gas flow rate. Would you expect the gas flow rate determined in this manner to be too high or too low ... 

Gas flows except for methane are metered by orifice gages calibrated by water displacement to within 1% for C02 and N2, respectively. Methane flow, much less critical, is determined by a Rotameter calibrated by calculation. All cooling water flows are determined by experimentally calibrated Rotameters. Cooling water temperature rise is determined by suitably graduated, interconsistent mercury thermometers. 

Rotameter (calibrated valve) Clear sotutions No siurriee.. aoostoOiio lOtol... 

Blockages or faulty pumps. Pumps should be checked periodically as instructed by the manufacturer. They can be calibrated using rotameters or bubble flowmeters. Unless pumps possess a limiting orifice they should be calibrated with the air indicator tube in position. 

Before removing the pump at the end of the sample period, check the flow rate to ensure that the rotameter bail is still at the calibrated mark (if there is a pump rotameter). If the ball is no longer at the mark, record the pump rotameter reading. 

Calibrate personal sampling pumps before and after each day of sampling, using either the electronic bubble meter method or the precision rotameter method (that has been calibrated against a bubble meter). 

The precision rotameter is a secondary calibration device. If it is to be used in place of a primary device such as a bubble meter, care must be taken to ensure that any introduced error will be minimal and noted. The precision rotameter may be used for calibrating the personal sampling pump in lieu of a bubble meter provided it is (a) Calibrated with an electronic bubble meter or a bubble meter, (b) Disassembled, cleaned as necessary, and recalibrated. It should be used with care to avoid dirt and dust contamination which may affect the flow, (c) Not used at substantially different temperature and/or pressure from those conditions present when the rotameter was calibrated against the primary source, (d) Used such that pressure drop across it is minimal. If altitude or temperature at the sampling site are substantially different from the calibration site, it is necessary to calibrate the precision rotameter at the sampling site where the same conditions are present. 

The checkers used acetylene available from Matheson Gas Products. The gas was purified by passing it through concentrated sulfuric acid and then through a tower filled with potassium hydroxide pellets. The gas was then passed into a 1-1. safety flask which was connected to the gas inlet tube by means of rubber tubing. The checkers used a rotameter that was calibrated with air to determine the flow rate of acetylene. 

Two commercially-available olfactometers, a Presser and a T04, were investigated physically and calibrated. The investigations showed that some operational problems of the Presser could be understood following a detailed physical examination. The T04 did not deliver the dilutions shown on the maker s calibration curves. The main problem with the T04 arose when flows were measured using the lower parts of the rotameter scales. The T04 could, however, function satisfactorily, a reproducibility within 5%, when only the upper parts of the rotameter scales were used. 

The Prosser was calibrated by measuring the air flows using a laminar flow meter (1% accuracy) for the odorous sample and a pitot tube with a micromanometer for the fan-blown air (3). The pitot pressures were converted to air velocities (4) and hence, from the cross sectional area of the tube, to volumetric flow rates. Since flow near the tube wall was slower than the centre, the tube was traversed by the pitot head and the average value calculated. A rotameter was also tried but it induced a back-pressure of 250 N/m2 and, as the manufacturer states that the maximum permissible back-pressure is 60 N/m for calibration to be accurate, its use was not pursued. 

The olfactometer was calibrated using C02, as the odorous gas, diluted in air to 10000 ppm by volume, and contained in a 30 1 Tedlar bag (Fig. 5) (7). C02-free oxygen was used as the diluting gas. The C02 concentration was was sufficiently low to avoid significantly altering the density of the odorous air. The bag was connected by silicon rubber tubing to the rotameter inlets and the diluted gas mixture was sampled via a tube placed inside the nose-piece and analysed by an infra-red gas analyser, with an accuracy of greater than 1% (Fig. 5). 

The theoretical dilution factors were calculated from the calibration graphs supplied with the olfactometer, for operation at 1, 2, 4 and 6><105 N/m2. The graphs plotted were the volumetric ratios of diluting gas odorous air against rotameter readings. These ratios were converted to dilution factors, in line with the values used with the Prosser, by the derivation shown below ... 

These investigations showed that the T04 olfactometer can deliver repeatable dilutions, but that an absolute calibration was needed before use. The main problems arise from the flow rates measured in the lower ranges of the rotameter scales, which are less accurate than the upper ranges. If the upper ranges only are used, then consistent results should be obtainable. The olfactometer should be used in the same orientation as when calibrated. 

The experimental setup for diode-laser sensing of combustion gases using extractive sampling techniques is shown in Fig. 24.8. The measurements were performed in the post-flame region of laminar methane-air flames at atmospheric conditions. A premixed, water-cooled, ducted flat-flame burner with a 6-centimeter diameter served as the combustion test-bed. Methane and air flows were metered with calibrated rotameters, premixed, and injected into the burner. The stoichiometry was varied between equivalence ratios of = 0.67 to... 

Rotameters require no straight runs of pipe before or after the point of installation. Pressure losses are substantially constant over the whole flow range. In experimental work, for greatest precision, a rotameter should be calibrated with the fluid which is to be metered. However, most modern rotameters are precision-made so that their performance closely corresponds to a master calibration plot for the type in question. Such a plot is supplied with the meter upon purchase. 

Figure 3. System used for calibration of the critical orifices 1, calibrated rotameter 2, 5, vacuum/pressure gauge 3, sampling manifold 4, orifice 6, vacuum pump.

Flowmeter. To monitor flow of carrier gas, a variety of devices are available, such as differential capillary, thermal conductivity, ionization, rotameters, and calibrated soap-film tubes Measurement of the flow may either be continuous or intermittent, and the flowmeter may be placed either in front of the column or at the carrier gas outlet. The soap-film type is most commonly used because of its economy and ease of operation. 

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