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4. Questions - Got a question about Gravimetry then search the Forums, FAQ's, Blogs etc. Don't be afraid to ask .....
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8. Security - check for the yellow padlock on the Gravimetry site before you buy, and the s after http:/ /i.e. https:// = a secure site
9. Contact - got a question about Gravimetry, or want to leave a comment then check out the sites contact page. Reputable companies have them and respond.
10. Payment - ready to pay for your Gravimetry, then use your credit card or PayPal! Be aware of companies that don't accept them, there may be genuine reasons but given the huge amount of choice you have when buying online there is no reason at all not to buy via credit card or PayPal.
Gravimetry is the measurement of a gravity field. Gravimetry may be used when either the magnitude of gravitational field or the properties of matter responsible for its creation are of interest. The term gravimetry or
gravimetric is also used in chemistry to define a class of analytical procedures, called gravimetric analysis relying upon weighing a sample of material.
Units of measurement
Gravity is usually measured in units of acceleration. In the
SI system of units, the standard unit of acceleration is 1 metre per second squared (abbreviated as m/s2). Other units include the
Galileo (unit) (sometimes known as a
galileo, in either case with symbol Gal), which equals 1 centimetre per second squared, and the
g-force (
gn), equal to 9.80665 m/s2. The value of the
gn approximately equals the standard gravity (although the actual acceleration
g varies fractionally from place to place).
How gravity is measured
An instrument used to measure gravity is known as a gravimeter, or gravitometer. Since general relativity regards the effects of gravity as indistinguishable from the effects of
acceleration, gravimeters may be regarded as special purpose accelerometers. Many
weighing scales may be regarded as simple gravimeters. In one common form, a spring (device) is used to counteract the force of gravity pulling on an object. The change in length of the spring may be calibrated to the force required to balance the gravitational pull. The resulting measurement may be made in units of force (such as the newton), but is more commonly made in units of Gal (unit)s.
More sophisticated gravimeters are used when precise measurements are needed. When measuring the Earth's gravitational field, measurements are made to the precision of microgals to find density variations in the rocks making up the Earth. Several types of gravimeters exist for making these measurements, including some that are essentially refined versions of the spring scale described above. These measurements are used to define gravity anomaly.
Besides
precision, also
stability is an important property of a gravimeter, as it allows the monitoring of gravity
changes. These changes can be the result of mass displacements inside the Earth, or of vertical movements of the Earth's crust on which measurements are being made: remember that gravity decreases 0.3 mGal for every metre of height. The study of gravity changes belongs to
geodynamics.
The majority of modern gravimeters use specially-designed quartz Hooke's Law#Zero-length springs to support the test mass. Zero length springs do not follow
Hooke's Law, instead they have a force proportional to their length. The special property of these springs is that a vertical pendulum can be designed with a period approaching a thousand seconds. This detunes the test mass from most local vibration and mechanical noise, increasing the sensitivity and utility of the gravimeter. The springs are quartz so that magnetic and electric fields do not affect measurements. The test mass is sealed in an air-tight container so that tiny changes of barometric pressure from blowing wind and other weather do not change the buoyancy of the test mass in air.
Spring gravimeters are, in practice, relative instruments which measure the difference in gravity between different locations. A relative instrument also requires calibration bycomparing instrument readings taken at locations with known complete or absolute values of gravity. Absolute gravimeters provide such measurements by determining the gravitational acceleration of a test mass in vacuum. A test mass is allowed to fall freely inside a vacuum chamber and its position is measured with a laser interferometer and timed with an atomicclock. The laser wavelength is known to ±0.025 ppb and the clock is stable to ±0.03 ppbas well. Great care must be taken to minimize the effects of peturbing forces such asresidual air resistance (even in vacuum) and magnetic forces. Such instruments are capable of an accuracy of a few parts per billion or 0.002 mGal and reference their measurement to atomic standards of length and time. Their primary use is for calibrating relative instruments, monitoring crustal deformation, and in geophysical studies requiring high accuracy and stability. However, absolute instruments are somewhat larger and significantly more expensivethan relative spring gravimeters, and are thus relatively rare.
Gravimeters have been designed to mount in vehicles, including aircraft, ships and submarines. These special gravimeters isolate acceleration from the movement of the vehicle, and subtract it from measurements. The acceleration of the vehicles is often hundreds or thousands of times stronger than the changes being measured. A gravimeter (the
Lunar Surface Gravimeter) was also deployed on the surface of the moon during the Apollo 17 mission, but did not work due to a design error. A second device (the
Traverse Gravimeter Experiment) functioned as anticipated.
Microgravimetry
Microgravimetry is a rising and important branch developed on the foundation of classical gravimetry. Microgravity investigations are carried out in order to solve various problems of engineering geology, mainly location of voids and their monitoring. Very detailed measurements of high accuracy can indicate voids of any origin, provided the size and depth are large enough to produce gravity effect stronger than is the level of confidence of relevant gravity signal.
History
The modern gravimeter was developed by Lucien LaCoste and Arnold Romberg in 1936.
They also invented most subsequent refinements, including the ship-mounted gravimeter, in 1965, temperature-resistant instruments for deep boreholes, and lightweight hand-carried instruments. Most of their designs remain in use (2005) with refinements in data collection and data processing.
See also
Gravimetry is the measurement of a gravity field. Gravimetry may be used when either the magnitude of gravitational field or the properties of matter responsible for its creation are of interest. The term gravimetry or
gravimetric is also used in chemistry to define a class of analytical procedures, called
gravimetric analysis relying upon weighing a sample of material.
Units of measurement
Gravity is usually measured in units of acceleration. In the
SI system of units, the standard unit of acceleration is 1
metre per second squared (abbreviated as m/s2). Other units include the
Galileo (unit) (sometimes known as a
galileo, in either case with symbol Gal), which equals 1
centimetre per second squared, and the g-force (
gn), equal to 9.80665 m/s2. The value of the
gn approximately equals the
standard gravity (although the actual acceleration
g varies fractionally from place to place).
How gravity is measured
An instrument used to measure gravity is known as a gravimeter, or gravitometer. Since
general relativity regards the effects of gravity as indistinguishable from the effects of acceleration, gravimeters may be regarded as special purpose accelerometers. Many weighing scales may be regarded as simple gravimeters. In one common form, a spring (device) is used to counteract the force of gravity pulling on an object. The change in length of the spring may be calibrated to the force required to balance the gravitational pull. The resulting measurement may be made in units of force (such as the
newton), but is more commonly made in units of Gal (unit)s.
More sophisticated gravimeters are used when precise measurements are needed. When measuring the Earth's gravitational field, measurements are made to the precision of microgals to find density variations in the rocks making up the Earth. Several types of gravimeters exist for making these measurements, including some that are essentially refined versions of the spring scale described above. These measurements are used to define gravity anomaly.
Besides precision, also
stability is an important property of a gravimeter, as it allows the monitoring of gravity
changes. These changes can be the result of mass displacements inside the Earth, or of vertical movements of the Earth's crust on which measurements are being made: remember that gravity decreases 0.3 mGal for every metre of height. The study of gravity changes belongs to
geodynamics.
The majority of modern gravimeters use specially-designed quartz
Hooke's Law#Zero-length springs to support the test mass. Zero length springs do not follow Hooke's Law, instead they have a force proportional to their length. The special property of these springs is that a vertical pendulum can be designed with a period approaching a thousand seconds. This detunes the test mass from most local vibration and mechanical noise, increasing the sensitivity and utility of the gravimeter. The springs are quartz so that magnetic and electric fields do not affect measurements. The test mass is sealed in an air-tight container so that tiny changes of barometric pressure from blowing wind and other weather do not change the buoyancy of the test mass in air.
Spring gravimeters are, in practice, relative instruments which measure the difference in gravity between different locations. A relative instrument also requires calibration bycomparing instrument readings taken at locations with known complete or absolute values of gravity. Absolute gravimeters provide such measurements by determining the gravitational acceleration of a test mass in vacuum. A test mass is allowed to fall freely inside a vacuum chamber and its position is measured with a laser interferometer and timed with an atomicclock. The laser wavelength is known to ±0.025 ppb and the clock is stable to ±0.03 ppbas well. Great care must be taken to minimize the effects of peturbing forces such asresidual air resistance (even in vacuum) and magnetic forces. Such instruments are capable of an accuracy of a few parts per billion or 0.002 mGal and reference their measurement to atomic standards of length and time. Their primary use is for calibrating relative instruments, monitoring crustal deformation, and in geophysical studies requiring high accuracy and stability. However, absolute instruments are somewhat larger and significantly more expensivethan relative spring gravimeters, and are thus relatively rare.
Gravimeters have been designed to mount in vehicles, including aircraft, ships and submarines. These special gravimeters isolate acceleration from the movement of the vehicle, and subtract it from measurements. The acceleration of the vehicles is often hundreds or thousands of times stronger than the changes being measured. A gravimeter (the
Lunar Surface Gravimeter) was also deployed on the surface of the moon during the Apollo 17 mission, but did not work due to a design error. A second device (the
Traverse Gravimeter Experiment) functioned as anticipated.
Microgravimetry
Microgravimetry is a rising and important branch developed on the foundation of classical gravimetry. Microgravity investigations are carried out in order to solve various problems of engineering geology, mainly location of voids and their monitoring. Very detailed measurements of high accuracy can indicate voids of any origin, provided the size and depth are large enough to produce gravity effect stronger than is the level of confidence of relevant gravity signal.
History
The modern gravimeter was developed by
Lucien LaCoste and
Arnold Romberg in 1936.
They also invented most subsequent refinements, including the ship-mounted gravimeter, in 1965, temperature-resistant instruments for deep boreholes, and lightweight hand-carried instruments. Most of their designs remain in use (2005) with refinements in data collection and data processing.
See also
Gravimetry Analysis
Wind Speed measured in knots) These four graphs are comparing the sigma of the readings from the Gravimeter with Wind Speed Data from the Met office between 18/02/2007 - 15/03/2007 ...
Gravimetry - Wikipedia, the free encyclopedia
Gravimetry is the measurement of a gravitational field. Gravimetry may be used when either the magnitude of gravitational field or the properties of matter responsible for its ...
Category:Gravimetry - Wikipedia, the free encyclopedia
Pages in category "Gravimetry" The following 14 pages are in this category, out of 14 total. Updates to this list can occasionally be delayed for a few days.
gravimetry - Hutchinson encyclopedia article about gravimetry
Hutchinson encyclopedia article about gravimetry. gravimetry. Information about gravimetry in the Hutchinson encyclopedia.
gravimetry - definition of gravimetry by the Free Online Dictionary ...
Definition of gravimetry in the Online Dictionary. Meaning of gravimetry. Pronunciation of gravimetry. Translations of gravimetry. gravimetry synonyms, gravimetry antonyms.
gravimetry - definition of gravimetry in the Medical dictionary - by ...
Definition of gravimetry in the Medical Dictionary. gravimetry explanation. Information about gravimetry in Free online English dictionary. What is gravimetry? Meaning of ...
gravimetry
Measurement of the Earth's gravitational field ... Tiscali Quicklinks. Please visit our Accessibility Page for a list of the Access Keys you can use to find your way around the ...
BIPM - gravimetry
Gravimetry ... Summary ICAG-2005: 7th International Comparison of Absolute Gravimeters (2005)
BIPM - time, frequency and gravimetry
Time, Frequency and Gravimetry ... You are here: scientific work > time, frequency and gravimetry
PM10 and PM2.5: Filter Gravimetry : Products & Services ...
Accurate weighing (gravimetry) of air filters is essential to support the growing number of International and European Standards methods being developed for a wide variety of air ...
