National Physical Laboratory

Can magnetic fields affect weighing? (FAQ - Mass & Density)

Yes, magnetic fields - and indeed magnetically permeable materials close to a balance - can effect a weighing result.

Most modern electronic balances, however, are relatively immune to external magnetic fields and problems encountered are most likely to be caused by the weights themselves.

There are two magnetic properties that must be measured to properly evaluate the magnetic characteristics of a weight - magnetic permeability and residual magnetisation

Magnetic permeability is a measure of a material's effect on a magnetic field in which it is placed. This creates a problem when weighing the material on an electronic balance since it affects the magnetic field of the sensing element and can modify the proper balance reading.

Residual magnetism is a measure of a material's ability to generate its own magnetic field. This can similarly affect the sensing element of an electronic balance but will also interact with other magnetically permeable materials - possibly inducing residual magnetism in them or causing stray forces.

OIML Recommendation R 111 sets out permissible limits for these two properties for various classes of weights. In Chapter 6, headed Material, paragraphs 6.2 and 6.3 include the following text:

  • 6.2 Class E1 and E2 weights

    The metal or alloy used for weights of classes E1and E2 shall be practically non-magnetic (magnetic susceptibility not to exceed k = 0.01 for class E1 and k = 0.03 for class E2 weights).
  • 6.3 Class F1 and F2 weights

    ..... The metal or alloy used for weights of classes F1and F2 shall be practically non-magnetic (magnetic susceptibility not to exceed k = 0.05).
Last Updated: 25 Mar 2010
Created: 8 Oct 2007

Registration

Please note that the information will not be divulged to third parties, or used without your permission

Login