Electronic bubble meter

Connect the tubing from the electronic bubble meter to the inset of the impinger/bubbler. 

Figure 2. For calibration, the cassette is attached to an electronic bubble meter as shown in the illustration.

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 electronic bubble meter method consists of the following ... 

Press the button on the electronic bubble meter. Visually capture a single bubble and electronically time the bubble. The accompanying printer will automatically record the calibration reading in liters per minute. 

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. 

Figure 7. The cyclone Li calibrated by placing the cyclone in a 1 liter vessel attached to an electronic bubble meter.

Of the RAS parameters, the gas flow rate has the greatest effect on volatility and must therefore be carefully controlled (Deibler et al., 2001). The flow rate of the effluent should be periodically measured to ensure flow rate consistency. The flow rate can be measured with a simple bubble meter or an electronic flow meter. Be sure the meter used is appropriate for measuring the magnitude of the anticipated flow rate. 

With capillary columns, we have many different flows to measure with extremely large differences in the range of flows. Capillary columns may have flows lower than 1 mL/min, yet have septum purge flows in the 2-5 mL range and splitter vent flows in the 100-300 mL range. It is preferred to measure capillary column flows in terms of linear gas rates. It is acceptable to measure the other flows with electronically controlled flow measuring devices or soap-bubble meters. Since the split ratio for an analysis is determined by dividing the flow of the column into the vent flow volume from the splitter, we normally do both of these flows electronically. Any other flows that are to be measured are not critical and either manually or electronic measurement is acceptable. 

With GCs made before the 1990s, carrier flow rate was controlled indirectly by controlling the carrier inlet pressure, or "column head pressure." The actual flow rate was measured at the outlet of the column or the detector with an electronic flow meter, or a bubble flow meter, and could be an involved, time consuming, and frustrating process. The pressure setting was not able to be varied during the run, and thus the flow was essentially constant during the analysis. The relation between flow rate and inlet pressure is calculated with Poiseuille s equation for compressible fluids. 

It is obvious that the flow rate must be precisely controlled. The pressure from the compressed gas cylinder of carrier gas, while sufficient to force the gas through a packed column, does not provide the needed flow control. Thus a flow controller valve is built into the system. The flow rate of the carrier gas, as well as other gases used by some detectors, must be able to be carefully measured so that one can know what these flow rates are and be able to optimize them. Flow meters are commercially available. However, a simple soap bubble flow meter is often used and can be constructed easily from an old measuring pipet, a piece of glass tubing, and a pipet bulb. See Figure 12.10. With this apparatus, a stopwatch is used to measure the time it takes a soap bubble squeezed from the bulb to move between two graduation lines, such as the 0- and 10-mL lines. The commercial version uses an electronic sensor to measure the flow rate based on the bubble movement. See Workplace Scene 12.3. 

B.J. Kronschnabel of the City of Lincoln, Nebraska, Water Treatment Plant Laboratory measures the flow rate of the gases at the outlet of the NPD detector using a electronic digital bubble flow meter. Notice the open door at the top of the GC in the background where the detectors and flow channels are visible. 

In contrast to other studies, oxidation carried out in this department on a Pt/7-Al203 catalyst has not uncovered any oscillatory behaviour in the temperature range of 100-185 °C. Addition of a hydrocarbon like but-l-ene, but-2-ene, or propene induces sinusoidal or relaxation type oscillations at temperatures above 150 °C. The experimental set-up used consists of a continuous recycle reactor system. The catalyst is packed in the cylindrical tubes. The gas flow rates are precisely measured with a bubble flow-meter. The reactor outlet is connected to a magnetic deflection mass spectrometer. An electronic peak select unit allows up to four mass numbers to be continuously monitored. The output data are connected to a PDP 11/45 computer for automatic and fast data logging. The data thus stored in the computer can be analysed later. The line diagram of the experimental set up is given in Figure 1. 

Figure 4.4.11. Schematic diagram of an IGC apparatus 1 - carrier gas, 2 - pressure reducer, 3 - gas cleaning unit (if necessary), 4+5 - gas-pressure regulation and control unit, 6 - manometer, 7 - column, 8 - thermostat, 9 - mechanical mixer, 10 - inlet syringe, 11 - detector (the gas flows after the detector through a bubble flow meter that is not shown here), 12 - electronics, 13 - recorder.

Stopwatch and bubble tube/burette or electronic meter. 

The apparatus used in our laboratory to measure water vapor permeability is schematically shown in Figure 10-4 (Tohge, 1996 Tadanaga, 1996) as an example. The sample to be evaluated is placed between two parts of the cell and clamped. The temperature of the sample can be controlled by the thermostat, or an electronic heater. Both sides of the sample in the permeation cell are evacuated to 10 Torr and the sample is degassed in the permeation apparatus for several hours. A saturated water vapor of at 0°C (4.58 mmHg) is then introduced to the upstream side and the pressure change on the downstream side due to the permeated water vapor is measured with a pressure meter. The water permeation coefficient (P) is evaluated from the increasing rate of the pressure (dp/dt) at a steady state and normalized with the thickness of the sample. When the vacuum line is not used, a test gas is supplied to the upstream side of the sample. The pressure difference between the upstream side and down stream side is determined and the flow rate is also measured, by, for example, soap-bubble displacement (Klein, 1990). 

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