GEM Scalar Magnetometers for Observation

Many magnetic observatories today rely on a combination of scalar, fluxgate and theodolite instruments for obtaining measurements. Research installations engaged in volcanology applications are also using scalar magnetometers for stationary work.

GEM’s Overhauser GSM-90 EUROMAG is particularly suited to these applications (and volcanology). This is a standard magnetometer without a display screen that can be operated via computer.

Observatory and Volcanology Applications

Up until about 10 years ago, magnetic observatories around the globe used fluxgate magnetometers as their primary tools to monitor the earth’s magnetic field. But fluxgates have the disadvantage that they must be periodically calibrated to maintain the level of absolute accuracy that is so important in observatory research.

By using an Overhauser magnetometer (EUROMAG) together with a fluxgate magnetometer, both total field and field direction information can be collected with a very high degree of absolute accuracy. (Users may also be interested in the GEM’s new Suspended dIdD magnetometer which can be accessed via the Vector Magnetometers product page.)

The EUROMAG instrument is the total field magnetometer/gradiometer of choice for customers who require:

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Minimal drift (0.05 nT/year)
Continuous, stable measurement
High absole accuracy (0.2 nT)
High sensitivity
Reliability (packaged in a thick, waterproof aluminum casing)
Convenient operation (RS-232C used for control and acquisition)
Low power operation (2Ws per reading – 0.5W average for 1 reading every 5 seconds)

The GSM-90 can be thought of as an Overhauser magnetometer (GSM-19) that has been simplified for long term monitoring applications. It has no keyboard, no battery and no memory for data storage. It is controlled by a terminal such as a Personal Computer which allows for its operation to be completely automated.

EUROMAG Benefits

The GSM-90 is a high sensitivity Overhauser effect magnetometer. Main benefits include:

The instrument is a secondary standard for measurement of the Earth’s magnetic field. The system has 0.01nT resolution, and 0.2nT absolute accuracy over its full temperature range.

The GSM-90 is available in two versions – a slow reading version and a fast reading version for flexibility. Each consists of one (170x70mm) cylindrical sensor, and a sturdy aluminum package (220x245x70mm) which contains all the unit’s electronics.

The instrument is microprocessor based for full remote control capability and time-savings. The results of measurement are available in serial form (RS-232-C interface) for collection by data acquisition systems, terminals or computers. The same RS-232 link provides the means of control to the instrument.

Understanding the GSM-90 Measuring Sequence

The GSM-90 is a compact version of the GSM-19 Overhauser magnetometer that:

Cycles from 0.2 seconds to 1 hour (depending on the version – Fast or Slow)
Includes a standard “Observatory” mode. Observatory mode measures over 5 second intervals and outputs an average value every minute. The time of the averaged reading is considered to be the time of the middle reading.
Can optionally be equipped with an AC deflect pulse (long or short) in order to minimize interference with other observatory instruments.

The instrument does not have a keyboard and display; therefore, all control of the instrument is through a computer or terminal.

GEMLinkW (PC Software) supplied with GSM-90 can be used for this purpose. Any other communication software commercially available (like Xtalk, Flashlink Mirror, Hyperlink etc.) capable of sending and receiving RS232 can also be used. Communication is very simple and requires sending only few bytes to the magnetometer.