Speaker: Chung Yin, Poon Calibration of Gaussmeters at Axial DC Magnetic Field Direction up to 1 Tesla at SCL Speaker: Chung Yin, Poon Standards and Calibration Laboratory (SCL) The Government of the Hong Kong Special Administrative Region

Measurement on DC magnetic flux density Measurement instruments Gaussmeter with Hall Effect transverse / axial test probe Nuclear Magnetic Resonance (NMR) gaussmeter Sources of magnetic flux density

Sources of Magnetic Flux Density Electromagnet Helmholtz Coils

Calibration on Axial Direction Test probe of the Reference Meter (located at the x-axis of the Helmholtz coil) Test probe of the DUT(located at the z-axis of the Helmholtz coil) B field direction

Calibration on Axial Direction B field direction x for axial measurement

Calibration Needs on Axial Field Toy Safety Standard ASTM F963-08 Section 8.24 Magnet Test Method Measurement parameter : magnetic flux density ( gauss / Tesla ) Equipment—dc field gauss meter with a resolution of 5 gauss (G) and an axial type probe. An active area diameter of 0.76 +/- 0.13 mm A distance between the active area and probe tip of 0.38 +/- 0.13 mm. Medical electrical equipment Safety (e.g. IEC 60601-2-33)

Automatic calibration system on DC magnetic flux density for working-grade gaussmeter in SCL

An automatic calibration system in SCL The major components of the system contain A modified electromagnet The electromagnet’s power supply A water cooling system for the modified electromagnet A reference gaussmeter A software controlled program

A modified electromagnet system in SCL Small opening at the yoke with size and shape suitable for positioning a common test probe in an axial magnetic field

Photos of the electromagnet Opening at the yoke test probe of the tested unit Filler rod test probe of reference meter

Characterization of the Modified Electromagnet Field Plot with the opening at the RHS yoke toward the RHS yoke with opening At the center of the yoke pole diameter = 150 mm ; pole gap = 20 mm; z-axis along the pole axis

Characterization of the Modified Electromagnet Field Plot with filler rod inserted in the RHS yoke pole diameter = 150 mm ; pole gap = 20 mm; z-axis along the pole axis

Setup of Calibration The measurement will be taken at the location adjacent to the LHS yoke ( i.e. as far away from the opening (i.e. RHS yoke ) )

Field Uniformity Z = 4 mm ; field uniformity ~ 500 x 10-6 Z = 7 mm ; On the surface of the LHS yoke

Automation of the calibration number of measurements; magnetic field levels for test; polarity of the test field ; settings of the reference meter ; settings of the UUT Test field levels are sorted in ascending order by the program Initial value = (Requested test level )/(electromagnet coefficient) The software tool using Visual Basic for the automatic calibration of working-grade gaussmter which have either IEEE 488, RS232 or USB interface.

Measurement Uncertainty Uncertainty contributions due to Field non-uniformity Calibration setup Performance of the test unit Performance of the reference meter Environmental effects The best calibration and measurement capability of the working grade gaussmeter is 0.1 % from 50 mT to 1.0 T for axial direction (k=2, 95% CL)

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