With the Franklin Tester Dr. Brockhaus Messtechnik GmbH & Co. KG (BROCKHAUS), Luedenscheid, presents yet a further instrument for measuring the quality features of soft magnetic materials. With this instrument it is possible to measure surface resistance, resistance distribution and, if required, the thickness of the coating on electrical steel and punched parts.

In transformers, generators and electrical motors the quality of the insulation has a direct influence on the efficiency and performance of these electrical machines. In extreme cases bad insulation can lead to undesirable overheating, eddy currents losses, short circuits and total failure. The consequences for manufacturers and users of electrical steel are increased costs, infringement of quality and damage to the company’s reputation.

By using the BROCKHAUS Franklin Tester it is possible, for example, to carry out random checks of the quality of the electrical steel supplied when it goes through the incoming goods control. In this way it is possible to avoid using badly insulated or damaged material. The Franklin Tester can just as easily be integrated in the production line. Faults affecting the quality are then detected early on in production and those faults which influence production can then be quickly remedied. Measurements are made according to IEC 60404-11 norm and ASTM standard A717-81.

The principle of the Franklin Tester

The Franklin Tester enables measurement of the total current which flows along the insulation coating of the sample when pressure is applied via several contacts. The measured value is converted into an equivalent surface resistance.

The Franklin Tester consists of three main components:
• voltage supply unit
• testing device with testing head and
• electronic hydraulic pump which sets the applied pressure to exactly the value required by the norm.

The testing head can be moved hydraulically perpendicular to a surface. It consists of two longitudinal rows of five vertically mounted steel rods which are free to move axially against the surrounding spiral springs. A stainless steel measuring contact is positioned at each end of each rod. The testing contacts are pressed on to the insulation coating with a pressure of 129N per electrode. An electrical contact to the steel sheet is made using a spiral drill. If the resistance is finite a current proportional to the resistance flows through the insulation coating.

Two measuring modes can be used with the Franklin Tester:

• Method A: Measurement of the insulation via all 10 electrodes
• Method B: Measurement of the insulation as a single resistance per electrode

The so-called “in line version“ is intended for use in existing production lines.
With BROCKHAUS FMA Expert software fully automatic measurement including comprehensive monitoring is possible. This software can be integrated quite easily into existing quality management systems and converts and archives or processes the data obtained, thus providing complete documentation of the measuring process. BROCKHAUS configures the measuring station and software to customer specifications.

BROCKHAUS also performs measurements to order in its own laboratory using the Franklin Tester.

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