Lake Shore Model 421 User Manual
                                                                                            | |
Contents
| 
Lake Shore Model 421 Gaussmeter User’s Manual5-10 Accessories and Probes5.4 REFERENCE MAGNETSMagnetic reference standards containing highly stable permanent magnets have been in use for manyyears. The highest quality units are usually shielded from external magnetic effects and use Alnico V orVI magnets for long-term stability. They are supplied in both transverse (flat) and axial configurations.Typical flat reference magnets are usually stabilized for use at ambient temperatures between0 – 50 °C and have nominal temperature coefficients of about –0.02%/°C. Because the temperaturecoefficient is negative, the field strength will be reduced as the temperature rises. Since thesereferences are temperature cycled during manufacture, their change with temperature is predictableand retraceable; they will always return to a known value at any specific ambient temperature.The high-permeability shell which surrounds the reference magnet serves two function: (1) it shields themagnet from external field, and (2) serves as the flux return path. Physical damage to the outer shellcan cause a permanent change in the gap flux density. Reference magnets should not be dropped orphysically abused. Magnets of this type can have magnetic reference values ranging from 100 G to20 kG, but the most widely-used value is 1 kG. Reference magnets accuracy is typically ±0.5%, exceptfor magnets of 200 G or less; for these magnets, the limit of error is generally ±1%. The referencemagnet gap is nominally 0.060 inch but may range from 0.040 to 0.250 inch for special units. Theusable "plateau" in the reference gap generally encompasses an area of about 0.5 square inches.In reference magnets used for axial field probes, Alnico V or VI is the usual magnet material, charged tosaturation and stabilized down to a particular value. The same temperature coefficients hold true as inthe transverse probe and the same care in handling must be observed. This assembly uses concentricmu-metal shield cans to protect the magnet from the effects of external magnetic field. Axial referencemagnets are available in values up to 1 kG, with 500 G being the most widely-used value.When a probe is inserted completely through the access guide, three distinct magnetic peaks will beobserved on the gaussmeter. One peak occurs as the probe enters the magnet, a second (and greater)peak is observed as the midpoint is reached, and a third (smaller) peak is read as the probe leaves themagnet. The calibration point is the largest reading in the midpoint area. Its amplitude will beapproximately twice that of the readings that occur where the probe enters or leaves the magnet.P-421-5-11.bmpFigure 5-11. Lake Shore Reference Magnets |
Related manuals for Lake Shore Model 421
This manual is suitable for:
manualsdatabase
Your AI-powered manual search engine