Lake Shore 475, Руководство пользователя

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Lake Shore Model 475 Gaussmeter User’s Manual
Background 2-3
2.1.5 DC Measurement
The DC mode should be used to measure static or slowly changing fields. When in DC mode, the instrument uses a
100 mA, 5kHz, square wave excitation current. The voltage that is generated by the Hall device is read by the A/D at
50 kHz and is then digitally processed using a product detector and a low-pass filter to create a DC reading. The readings
are then averaged using a configurable averaging filter that can give a high-speed reading or a low-speed, high-resolution
reading. Refer to Paragraph 4.6.2 for information on how to set the DC filter. Analog Output 2 can be used to output a
digitally derived, DC representation of the field being measured over the DC frequency band.
Figure 2-2. DC Measurement Block Diagram
2.1.6 RMS Measurement
The Model 475 offers two different modes of AC measurement, narrow-band and wide-band. In narrow-band AC
measurement, the instrument uses a 100 mA, 5 kHz, square wave excitation current. This type of excitation provides the
benefit of noise cancellation characteristics of the product detector but limits the maximum frequency to approximately
1 kHz. The voltage that is generated by the Hall device is read by the A/D at 50 kHz and is then digitally processed using
a product detector and a low-pass filter to create a broadband AC reading. The readings can then be passed through a
selectable band-pass or low-pass filter before the RMS calculation is made. Refer to Paragraph 4.7.2 for information on
how to set the AC filter. Analog Output 2 can be used to output a digitally derived, AC representation of the field being
measured.
Figure 2-3. RMS Narrow Band AC Block Diagram