1. 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

2. 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

3. Sources of Magnetic Flux Density
Electromagnet
Helmholtz Coils

4. 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

5. Calibration on Axial Direction
B field direction x
for axial measurement

6. Calibration Needs on Axial Field
Toy Safety Standard
ASTM F 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 / mm A distance between the active area and probe tip of / mm.
Medical electrical equipment Safety (e.g. IEC )

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

8. 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

9. 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

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

11. 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

12. 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

13. 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 ) )

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

15. 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.

16. 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)

17. Thank you