Technical Notes

Occupational Magnetic Fields Guidelines for DC Fields

The biological effects of AC fields are detectable at much lower levels than for DC fields. It is therefore inappropriate to use the AC field Guidelines for DC fields. A good source of information on DC Fields is the Medical College of Wisconsin site “Static Electric & Magnetic Fields and Human Health: Questions & Answers“. Question 20, “Do exposure standards for static electric and magnetic fields exist?” provides a good summary of Guidelines for DC Fields.
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Magnetic Units

Conversion of Gauss to Tesla:
1µG = 0.1nT, 1mG = 100nT, 1G = 100µT, 10G = 1mT, 10,000G = 1T

Relationship between Magnetic Flux Density (B) and Magnetic Field Strength (H):

In vacuum (or air) B=µoH. For SI units µo = 4pi x 10-7H/m, B is expressed in Tesla and H in Ampere turn/m or A/m. Hence in vacuum or air a flux density of 1T = 796kA/m.
For cgs units µo = 1, B is expressed in gauss and H in oersted. Hence in vacuum or air a flux density of 1 gauss = 1 oersted.
For further information visit the NIST Reference on Constants, Units, and Uncertainty


Magnetic Field Vectors and Components

The magnetic field at any point in space is a vector quantity. This means there is a direction associated with the field as well as a field strength. Consider the arrow below:

The direction of the arrow can be thought of as the direction of the magnetic field. The length of the arrow can be thought of as the strength of the field, i.e. the longer the arrow, the stronger the field. Call this length B.
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Metrolab 2025 NMR Teslameter (Gaussmeter), 1060 & 1062 Deuterium Probes and their Residual H Signal

The Metrolab 1060 and 1062 range 6, 7 and 8 NMR Probes use a heavy water (D20) liquid sample in a glass vial. The sample has a small amount (less than 1%) of H20 contamination.

Early in 2000, Michael Duffy improved the rf performance of the range 8 NMR Probe. The result of this has improved the sensitivity for both the proton and deuterium resonances by over 300 percent. In the past, the lower proton resonance signal from the deuterium probes may have been too weak to ‘lock’ the NMR Teslameter (Gaussmeter). With the probe improvement and the probable improvement in unshimmed magnet uniformity it is likely that both the proton and deuterium resonances will be seen by the automatic tracking circuits of the NMR Teslameter (Gaussmeter).
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RoHS and WEEE Compliance

The EU’s Restriction of Hazardous Substances (ROHS) Directive 2002/95/EC, often referred to as the “lead free” directive, restricts the use of certain hazardous substances in the design and production of electrical and electronic equipment. It is closely linked with the Waste Electrical and Electronic Equipment (WEEE) Directive 2002/96/EC which sets collection, recycling and recovery targets for electrical goods and is part of a legislative initiative to solve the problem of huge amounts of toxic waste.
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Comparison of Danfysik 867-400 and LEM IT 400-S current transducers

The Danfysik 867-400 offers many of the same specifications and is a direct in-kind replacement for the LEM IT 400-S.
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Typical Bergoz IPCT-100mA response time

Test data of the Bergoz IPCT-100mA response time.
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Danfysik Current Transducer: “Wrap around” or Distributed Primary Current Cable

GMW offer a “wrap around” Primary Cable with three returns for a 600A Transducer and a similar wrap around Primary Cable for a 2000A Transducer with four returns.The advantages of this wrap around arrangement for high accuracy, broad frequency range measurements are:
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Effects of Environmental Magnetic Field on Model 5451 Helmholtz Coil Electromagnet

The Model 5451 Electromagnet is a Coil pair arranged in approximately Helmholtz geometry. It has no magnetic shielding and hence the magnetic field within the central volume is the vector sum of the field created by the Helmholtz Coil and the environmental magnetic fields at the same location.
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Bergoz Current Transformer: Power line Fault Detection- Keeping the Electricity flowing in South Africa

Bergoz Current Transformers have been employed in an interesting application to detect faults in the electricity supply lines in Southern Africa. ABB successfully installed Bergoz CTs recently and the system described below is now operational in the field.
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