Lake Shore Model 421 User Manual
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Lake Shore Model 421 Gaussmeter User’s Manual3-4 Operation3.3 AC/DCPressing the AC/DC key toggles between AC and DC measurements. The annunciator immediatelychanges from DC to RMS, as applicable. However, one update cycle is required for a new display value.In DC operation, the display shows the DC field at the probe with sign (orientation) followed by theappropriate field units and the letters DC. The DC value is available over the Serial Interface and bothAnalog Outputs. The resolution of DC readings is 3¾ digits when the filter feature is turn off and4¾ digits when the filter is turned on.In AC operation, the RMS readings will meet specified accuracy from 10 to 400 Hz. The AC RMS valueis defined as the square root of the average of the square of the value of the function taken throughoutone period. Frequency response and noise dominate the error present in AC mode. The Model 421 hasa predictable frequency response which is illustrated in Figure 3-3.The RMS value is available over the Serial Interface. A DC voltage representation of the RMS displayreading is available from the Corrected Analog Output, while a true analog waveform is available fromthe Monitor Analog Output. (In fact, the Monitor Analog Output is not affected by the selection of ACor DC.) The resolution of AC RMS readings is fixed at 3¾ digits.P-421-3-3.bmpFigure 3-3. Model 421 AC Frequency Response3.4 DISPLAY FILTERThe display filter function is used to quiet the display and make it more readable when the probe isexposed to a noisy field. Care should be taken when using the filter on changing fields because it maylevel off peaks and slow the response of the instrument. The filter also acts to quiet noise within theinstrument, making an additional digit of usable resolution available with the filter on in DC. The filterfunction makes a linear average of 8 readings and settles in approximately 2 seconds.To turn on the display filter, press and hold the AC/DC key for 5 seconds. The following display willappear.Select With °®Filter On ¡OffUse the s or t keys to toggle between On and Off. Press the Enter key to accept the new setting. |
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