Barometric pressure compensation

Wrong The chief engineer failed to realize that the vacuum pressure indicator was not equipped with a barometric pressure compensator. An ordinary vacuum pressure indicator or pressure gauge reads the pressure difference between the vacuum system and atmospheric pressure. When ambient temperatures drop, the barometer rises or ambient pressure goes up. An ordinary vacuum pressure gauge or indicator would then read an improved vacuum. But in reality, the vacuum has not changed. 

TTie HP 6890 series features electronic pneumatics control which provides complete electronic control of all gas pressures and flows. On-board sensors automatically compensate for ambient temperature changes and barometric pressure differences to provide more accurate and reproducible results routinely. This reduces recahbration frequency and improves laboratory productivity. It also decreases system operating costs, allows a faster set-up time, and reduces equihbradon time after set-points are changed from one method to the other. 

Automated water-level measurement can be achieved by deploying pressure transducers that can be set to log data as frequently as every second if required. Loggers also record temperature and are able to compensate for altitude, water density, temperature and barometric pressure. These are routinely used when undertaking hydraulic tests on a well but are also useful to provide accurate, regular, longterm water level data and are invaluable for groundwater flow direction calculations. 

Differential pressure sensors are used to measure the bed pressure, leaving one leg open to the atmosphere to compensate for barometric pressure variations. Care must be taken in the installation to minimize the plugging with solids. This is normally done by tilting the tank nozzle on which the DP cell is mounted downward from the sensor, so the solids tend to settle away from the sensor surface. A shutoff valve and washer flush tap are recommended to allow easy maintenance. 

Instruments very sensitive to sample flow must be compensated for barometric pressure. 

A very common layout for the assembly of condensers is barometric installation, the method in which no pump is needed to extract the liquid from under vacuum. The condenser is erected at such a height above the liquid drain level that the pressure difference between the vacuum inside the condenser and the atmospheric pressure is compensated by a liquid column. The height of this barometric leg must also overcome the flow resistance. In Figure 2.15, such a barometric installation is shown for a unit employing surface condensers. The height between the condensate outlet at the condenser and the liquid surface level in the collecting tank can be calculated by the necessary pressure difference and the specific weight of the... 

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