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Vol. 9  No. 4

ABSOLUTE vs. GAUGE PRESSURE

&
**NEW** YSI EQUIPMENT

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Absolute vs. Gauge Pressure

Pressure head measurements are common in groundwater monitoring, remediation and management. The use of pressure transducers and data loggers makes collecting a large number of measurements much easier, however it is important to understand what pressure the transducer is recording, and how, if necessary, to convert it to the measurement required. More specifically, it is important to understand the difference between absolute and gauge pressure, and to understand which of these your pressure transducer measures. This newsletter will outline the differences between the two pressure measurement types.

Absolute Pressure is relative to zero pressure; indicative of how much higher the pressure is relative to a vacuum, where no pressure exists. Absolute pressure transducers are not vented to the atmosphere.

Gauge Pressure is relative to atmospheric pressure; it is the difference between the pressure the transducer records and the pressure in the atmosphere. Gauge pressure transducers are vented to the atmosphere so that the transducer can measure pressure in the borehole relative to that of the atmosphere.

There are transducers that record absolute pressure, and there are also others that record gauge pressure.  It is important to know the difference between the two, as you may need to convert to/from gauge or absolute pressure. In groundwater studies it is common to want the gauge pressure, or to know the pressure head in the borehole relative to the atmospheric pressure, isolating the pressure derived from the groundwater and porous matrix. Therefore, absolute pressure data would need to be converted using barometric data, as the pressure in the surrounding atmosphere changes with time. Conversion from absolute to gauge pressure simply requires subtracting the atmospheric pressure from absolute pressure.

There are obvious advantages and disadvantages to both absolute and gauge (or also called vented) transducers.  The gauge pressure transducers do not require converting the pressure using barometric data, as the absolute pressure transducers would.  However, some scientists feel that actual barologger data allows for more precise measurements relative to the gauge or vented transducers.

GroundwaterSoftware.com supplies both absolute and gauge pressure transducers, and is proud to introduce a new equipment supplier to our line-up, YSI Equipment.

References

 

Fetter, C.Q. (1994). Applied Hydrogeology. Published by Maxwell Macmillan International, New York.

Freeze, R.A, and Cherry, J.A. (1979). Groundwater. Published by Prentice Hall, Inc., New Jersey.

Driscoll, F.G. (1995). Groundwater & Wells, Second Edition. Published by Johnson Screens, Minnesota.

 

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**NEW** YSI EQUIPMENT

Whether you are concerned with floods, droughts, storm water runoff, clean drinking water, or healthy ecosystems, YSI can prove to be a valuable partner. Their instruments, software, and data collection platforms are focused on environmental monitoring and testing. The integrated systems they deliver to their customers helps them to obtain critical data about the quantity and quality of water.

YSI is your one-stop source for environmental water quality monitoring instrumentation, offering single and multiparameter instruments, integrated systems, and accessories for most unattended monitoring, water quality sampling, profiling and logging applications.

YSI ground water instruments can be used with flow cells to easily pump water through the cell to provide continuous flow past the probes. This also prevents placing instruments in the well.

Solutions for ground water sampling or monitoring include instruments to measure temperature, level, dissolved oxygen, pH, ORP, conductivity and turbidity.

Data logging, PC connectivity, and desktop software for data management make your job easier and enables you to be confident in your data.

For more info click here:  YSI
To purchase click here: Order Online

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