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Electrical conductivity in materials - Measuring techniques

Jakob S. Engbæk

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Electrical conductivity in materials - Measuring techniques

In order to measure the conductive properties of materials, different techniques are used depending on resistance:

At relatively high resistance, an Agilent 4339B High Resistance Meter with an Agilent 16008B Resistivity Cell is used.  Using this equipment it is possible to measure resistivity/volume resistance up to 4.0 ·1015 Ohm cm and surface resistance up to 4.0·1015 Ohm.

At higher conductivity, where the contact resistance becomes significant, 4-point measurements are done with a Keithley 2400 SourceMeter to determine the resistivity in the materials. For metals with even higher conductivity we used a seperate powersuply that can delivere up to 100 A. This enable reliable measurements down in the 0.1 mili Ohm range.

 For composite materials, where it is important to know the conductivity through eg a plate, we have developed techniques for this particular measurement. Properties lengthwise and crosswise may be different if the composite is filled with fibres or flakes, which have been oriented eg during casting. For measurements of surface resistivity, ring electrodes are used as described in the standards.

Measurements are usually done at well defined temperature (23 ⁰C) and humidity (RH = 50 %), which are the standard conditions for measurements according to ASTM D257-14, ASTM D4496-04, ASTM D991-89(2005) or IEC 60093. If one wishes to make measurements on protective clothing according to DS/EN 1149-1, the measurements must be done at a relative humidity of 25 ¡¾5 %. These measurements are carried out in a climatic test cabinet where the temperature and humidity can be varied over a large range, so other conditions are also posible.

The methods described above are not limited to measurements on polymer materials; they are also well suited for other materials with a comparable conductivity, ie. from about 0.01 Ohm cm to 4.0 E+15 Ohm cm. Furthermore, DTI have experience with measuring the resistance of composites, rubber, textiles and metal structures.

Billedet viser en del af udstyret til måling af volumen og overflademodstand 

Part of the equipment for volume and surface resistance Measurements.
 

 
De 2 ovenstående fotos viser Agilent 16008B Resistivity Cell til måling på flade prøveemner: Min. Ø50 mm, Max. 120 mm x 130 mmDe 2 ovenstående fotos viser Agilent 16008B Resistivity Cell til måling på flade prøveemner: Min. Ø50 mm, Max. 120 mm x 130 mm 
Agilent 16008B Resistivity Cell for measurement on flat samples: Minimum diameter 50 mm, max. 120 mm x 130 mm