Lake Shore 475, Руководство пользователя

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Lake Shore Model 475 Gaussmeter User’s Manual
3-6 Installation
3.5.3 Probe Accuracy Considerations
The user must consider all the possible contributors to the accuracy of the reading. Both the probe and gaussmeter have
accuracy specifications that may impact the actual reading. The probe should be zeroed before making critical
measurements. The zero probe function is used to null (cancel) out the zero offset of the probe or small magnetic fields.
It is normally used in conjunction with the zero gauss chamber, but may also be used with an open probe (registering the
local earth magnetic field). Users wishing to cancel out large magnetic fields should use the Relative function. Refer to
Paragraph 4.6.6.
Probe temperature can also affect readings. Refer to the two separate temperature coefficients listed on the specification
sheet. The High Stability (HST) probes exhibit a low temperature coefficient of gain due to the inherent thermal stability
of the materials used in its construction.
Probe readings are dependent on the angle of the sensor (Hall sensor) in relation to the magnetic field. Maximum output
occurs when the flux vector is perpendicular to the plane of the sensor. This is the condition that exists during factory
calibration. The greater the deviation from orthogonality (from right angles in either of three axes), the larger the error of
the reading. For example, a 5° variance on any one axis causes a 0.4% error, a 10° misalignment induces a 1.5% error,
etc. See Figure 3-5.
Tolerance of instrument, probe, and magnet must be considered for making critical measurements. The accuracy of the
gaussmeter reading is typically ±0.05% of reading and ±0.005% of range, but the absolute accuracy readings for
gaussmeters and Hall probes is a difficult specification to give, because all the variables of the measurement are difficult
to reproduce. Differences in alignment and positioning will degrade measurement accuracy and repeatability. Finally, the
best probes have an accuracy of ±0.10%. This implies that the absolute accuracy of a magnetic field measurement will
not reliably be better than ±0.10% of reading, and is likely to be 0.20%.
Figure 3-5. Effect of Angle on Measurements