Magnetic field measuring instruments

General introduction

Measurement of magnetic fields is quite a complex task from a technical point of view. It is necessary to delimit the magnetic field of interest:

  1. Is field strength H [A/m, A/cm] or flux density B [T, mT or Gauss] measured?
  2. What is the intensity of the magnetic field or flux density? (nanoTesla / mictroTesla / milliTesla / Tesla)
  3. Is a steady field (DC), sinusoidal alternating field (AC), non-sinusoidal alternating field (AC) or a short pulsed field (AC or DC) measured?
  4. If AC field is measured: is the peak or RMS value of interest? What are the frequencies (Hz / KHz / MHz / GHz)?
  5. Is only one direction of the magnetic field (1D) or are all three spatial directions (3D) measured independently? Or is the space vector measured?
  6. Is the field near the object surface measured or is the magnetic field measured at a greater distance from the field source?

The selection of the magnetic field measuring device (also called Teslameter, Gaussmeter or magnetometer) essentially depends on the above mentioned questions.

Cestriom GmbH is providing solutions in industrial demagnetization. The devices and explanations below focus on the measurement of residual magnetism on steel parts. Viable measuring results form the basis for deciding whether further measures with regard to demagnetization must be taken.

Measurement of residual magnetism

In this specific application, the Gaussmeters are mainly used by industrial enterprises for quality assurance purposes (application areas for more information). The requirements are as follows:

  • Measurement of magnetic flux densities or field strengths on part surfaces in the range of approx. 0,1 Gauss to max. approx. 250 Gauss or approx. 0,1A/cm to max. 200A/cm.
  • Measurement of DC field.
  • Directional measurement of the field component (1D) emerging from the surface by use of a tangential probe (or alternatively an axial probe).
  • Measurement close to the surface of the part (with probe contact on surface).

At the moment there exists no general standard for the industry according to which the manufacturers of Gaussmeters can be directed. In order to minimize deviations between measurements (supplier -> client), some important factors are explained below.

Important influencing factors on the measurement result

Measuring distance

The measuring distance is a decisive influence. The measuring distance from the active measuring element (Hall sensor) when placed flat on the surface of the object, depends on the Gaussmeter type. Common measuring distances of Hall Gaussmeters on the market usually range from ~0,3mm to ~2,0mm. The frequently used analog Gaussmeters with round housing (no Hall sensor) work with a measuring distance approximately corresponding to 16mm or more.

We recommended a small measuring distance. Under this circumstance it might be reasonable to set the residual magnetism limit values ​​slightly higher than the frequently used limit values. The goal is to get a better controllable quality control. As an example, a limit of 2 Gauss at a measuring distance of 2mm is less demanding than a limit value of 5 Gauss at a measuring distance of 0,7mm (this applies in particular to fine pole residual magnetism on ferromagnetic parts).

The measuring results in the range of interest of approximately 1…6 Gauss thus differ considerably (sometimes up to a factor of 10 or more) depending on the type of measuring instrument used.

Ambient magnetic field

The ambient magnetic field (earth magnetic field and possibly further magnetic fields) existing at the measurement location is inducing magnetic fields in the measured component. The magnitude of the induced field depends on the orientation of the part relative to the ambient magnetic field vector, the magnetic permeability and on the slenderness ratio of the measured part. The induced fields usually lead to measurement fluctuations of a few Gauss especially on edges and ends of a part. These fluctuations are particularly evident in the case of manual measurement. The reason is the changing orientation of the probe and the measured object from measurement to measurement.

Search methodology

The search methodology with the probe relative to the surface of the component is also a decisive influence. Has the highest magnetic field spot on the surface of a part been discovered? The human influence plays an important role.


Products

Gaussmeter FM302

Our magnetic field measuring devices are manufactured by a specialized company. We sell the products as a re-seller.

The Gaussmeter FM302 universal hand-held measuring instrument is consisting of a display unit and a pluggable magnetic field probe. Different probe types are available. For the measurement of residual magnetism the tangential probe AS-LTM is the right solution in most of the cases.

Gaussmeter FM302 with options
Gaussmeter FM302 with options

Available probes:

Axial probe: sensitive direction parallel to the lance

Tangential probe: sensitivie direction perpendicular to the lance

Main software functions (included):

  • Displaying results on Windows PC
  • Adjustable limit value
  • Oscilloscope like display function
  • export of measured values to Excel etc.
Gaussmeter FM302
Measurement: Magnetic field DC / AC (RMS)
Measuring range: Depending on probe, x1, x10, x100
Bandwidth (-3dB): DC: DC up to 100kHz                                                      AC: ~5Hz up to 100kHz
Measurement uncertainty DC: x1: <0,1% +/- 2 digit                                                       x10: <0,1% +/- 5 digit                                                   x100: <0,1% +/- 20 digit
Adjustable offset (zero point): +/-4’500 digit in the range x100
Measurement uncertainty AC (RMS): 16,7Hz <= -0,3dB                                                          50Hz <= -0,1dB
Operation: Foil keyboard
Supply: 9V battery / power supply
Display: LCD 4 ½ digit
Resolution: 1/20’000 of probe measuring range
Representation of the measured values: Average (DC)                                                          Effective value (AC / true RMS)
Display mode: Absolute                                                                       Relative                                                                     Minimum (peak value memory)                        Maximum (peak value memory)
Units: Tesla, Gauss, Oersted, A/m
Refreshing rate: Adjustable 0,1s up to 5s
Digital filter: Averaging filter with length 1 up to 64 values
Tangential probe AS-LTM
Measuring range with Gaussmeter device FM +/- 2mT; +/-20mT; +/-200mT
Probe dimensions WxLxH: 5x70x1.4mm
Linearity error: <0,2%, +/-0,1mT
Measuring distance sensor <-> surface: ~0,7mm
Wear resistance probe: good – very good (Hallsensor inside brass tube)
Axial probe AS-LAP
Measuring range with Gaussmeter device FM +/- 2mT; +/-20mT; +/-200mT
Probe dimensions DxL: 6x180mm
Linearity error: <0,5%, +/-0,1mT
Measuring distance sensor <-> surface: ~0,4mm
Wear resistance probe: medium

Delivery:

  • Gaussmeter FM302
  • Software on CD
  • Probe(s) of your choice
  • Factory calibrated Gaussmeter and probe(s)
  • Hardcase for measuring instrument, probes and accessories

Available Options:

  • Zero chamber for zero adjustment without magnetic field of earth

The Gaussmeter FM302 can be used for various purposes using other probes (not listed above). Contact us if interested.


AS probe adapter

The AS probe adapter is used for permanently installed measuring tasks. The measuring system is composed of the AS probe adapter, a probe, power supply and an analog signal evaluation unit, e.g. PLC or industrial PC.

probe adapter
probe adapter

The same probes are used by the AS adapter as by the Gaussmeter FM302.

Examples:

  • Checking residual magnetism on components in automated production
  • 100% residual magnetism control after demagnetization process
  • Process monitoring of demagnetization processes