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Mouse click into the world of gravity

On the Web pages of PTB, a new information platform has been created where interested persons from physics and industry can inform themselves about the local intensity of the gravitational field of the Earth, relative to the respective place of use.

The Gravity Information System can be found on PTB's web pages under:Department 1.1, Mass (klick on picture)

Today, the majority of modern, electronic weighing instruments are used without compensation weights and must, for their place of use, be adjusted to the local influence of the gravitational field of the Earth. In addition to the traditional method – i.e. adjustment of the "correct" display value with the aid of adjusting weights at the place of use – a computational correction of the weighed value can also be made already at the manufacturer's, taking into account the acceleration due to gravity valid at the place of use.

With the Gravity Information System (GIS) developed at PTB, a simple, graphically supported means for the calculation of gravity values (acceleration due to gravity) is made available world-wide which works as the route planners known from the Internet. An interactive map section, based on a digital atlas data base, allows any map section of the Earth and thematic backgrounds of the gravitational field to be represented with the aid of a few map control elements. The indication of a gravity value or of a gravity anomaly relative to the place can be generated by entering the name of a place, the coordinates of a place (longitude, latitude, altitude), or by a mouse click into the map.

A four-stage gravity data model, which is mainly composed of freely disposable secondary – i.e. derived – gravitational field quantities, serves as a database. On the basis of a global geo-potential model which ensures global coverage, regionally higher resolved data sets are used for compression. For the derivation of selective gravity values, a reduction method at sea level is used – including a global height model – to be able to determine relative uncertainties of up to < 10–6 , at least, however, of ~5 · 10–5, on a mathematically slightly curved surface with the aid of a geostatistic interpolation approach. In this way, the requirements of a very large part of metrological applications carried out under the influence of the gravitational field are complied with, without local gravimetric measurements being necessary.

In weighing technology it is, in addition, of advantage to have a spatially extended validity range defined for the gravity value at the place of installation which is used for the calibration. This range, the so-called gravity zone, can be calculated with the aid of the GIS as a function of the weighing instrument type to be used, and represented in a pre-selected map section. In addition, further thematic representations of the field of gravity can be viewed as graduated coloured pictures in combination with explanatory isolines in the map section.

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