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Magnetic measurements

TO REMEMBER
100 uT (microTesla) = 1 Gs (Gauss)
100 nT (nanoTesla) = 1 mGs (milliGauss)
in air or vacuum

We provide an environmental magnetic measurements service. The frequency range we can measure with good reliability goes from 0 (Zero) Hz to about 10 kHz, while signal spectral analysis is also possible in some cases. According to the field frequency, its strength and measurement purposes, we use one kind of sensor or another. In many cases we can employ a triaxial probe wich provides to us the three field components simultaneously. The measure resolution could reach 1 nT, approximately (depending on the scale).

We differentiate two kind of measurements: Continuous Recording on a fixed point (it is more time function) and Magnetic Survey, by measuring the field in several spatial points (it is more space function). In some cases both are performed, with two or more instruments. Continuous recording is suitable when field variations are of interest, whereas in a magnetic survey the total field value static or alternate, on each point, is usually recorded, sometimes with its three components individually.

Continuous Recording Normally its is done with a Bartington Mag-03MC-1000 probe, on three axes, or with a Bartington Mag-01H magnetometer, on one axis.

The analog signals are converted to digital ones (10 bits) and sent to a portable PC for its recording during a time as necessary (from minutes to 24 hours, or more).

This is an ideal modality to record magnetic fluctuations from 0 to 10 Hz which, together with the 50 Hz from power network, are usually the major contributions to magnetic noise in urban environments.

It is commonly used during instalation planning (or to solve problems) of equipment sensitive to these fields, such as MRI (Magnetic Resonance Imaging) systems, electron microscopes, etc.

Magnetic Survey That is the measurement on several, or many, spatial points in order to know the field value for each one. That allows to study the magnetic field "shape" or its gradients. That could be along one line (direction), on a plane or in volume distributed points.

It is performed with the above mentioned instruments, or with inductive sensors, sometimes more practical when studying an alternating field (50 Hz, for example), or with Hall Effect probes. The values are recorded in relation with a site and/or equipment under study drawing.

It is normally used to study the field generated by some device. As examples: a transformer (50 Hz) or a MRI (Magnetic Resonance Imaging) magnet, in which the "5 Gauss line" (0 Hz) is of interest often. That also allows to locate the origin for hidden wires produced magnetic field (50 Hz), or to study the local terrestrial magnetic field deformations due to ferromagnetic masses, etc.

One recording example
Magnetic recording example - low resolution
(Click on the image to see a more detailed one)
Fluctuations produced by one electric railway which track is at about 50 m from the magnetic probe, parallel to its X axis. A 50 Hz noise from the local network is superimposed.

The used probe was the Bartington Mag-03MC-1000, on three axes. The signal conditioner section allows us to apply low-pass filters (about <15 Hz) for 50 Hz suppression for better appreciate the ultra low frequency fluctuations, as can be seen in here.

The data logger is programmed to show half-hour long "pages". At the end of each one it is saved as a self-indexed file, including its start time and date, starting the next page immediately. In that way 24 h recordings, or more, are possible.

The original file was converted to .GIF format and related annotations were added for report purposes. The most interesting field component for the study objetive was the vertical one (Z), in that case.

To check that meter operation and selected range (scale) are right, we usually introduce the probe into a calibration coil to which we supply current pulses, in order to produce magnetic pulses of known amplitude. An 1 microT (10 mGs) pulse is visible in here.

By clicking in here you can see the Mag-03 probe specifications on Bartington´s site.

Diverse sites and its probable magnetic fields can be very different in between them. There is also a huge variety of needs and equipments to be studied. Due to all the former every magnetic measurement must be planned in advance to determine the procedure to follow. Serviciencia has a long time experience in this topic and we have well stablished protocols for some typical situations, such as in the case of Magnetic Resonance Imaging (MRI) systems, for instance. That might be taken into account when we are asked for a quotation, since its amount depends on measurements complexity and time expended on these, including its preliminaries.

To those who want to perform that kind of measurements for themselves, Serviciencia can supply them with the necessary instruments from Bartington Instrument Ltd and Metrolab Instruments SA firms, with our advise for set-up and application as one added benefit.

Please, do not hesitate in asking us.


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Updated: 31 Oct  03

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