Lake Shore Model 421 Gaussmeter User’s Manual
3-4
Operation
3.3 AC/DC
Pressing the
AC/DC
key toggles between AC and DC measurements. The annunciator immediately
changes 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 the
appropriate field units and the letters DC. The DC value is available over the Serial Interface and both
Analog Outputs. The resolution of DC readings is 3¾ digits when the filter feature is turn off and
4¾ 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 value
is defined as the square root of the average of the square of the value of the function taken throughout
one period. Frequency response and noise dominate the error present in AC mode. The Model 421 has
a 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 display
reading is available from the Corrected Analog Output, while a true analog waveform is available from
the Monitor Analog Output. (In fact, the Monitor Analog Output is not affected by the selection of AC
or DC.) The resolution of AC RMS readings is fixed at 3¾ digits.
P-421-3-3.bmp
Figure 3-3. Model 421 AC Frequency Response
3.4 DISPLAY
FILTER
The display filter function is used to quiet the display and make it more readable when the probe is
exposed to a noisy field. Care should be taken when using the filter on changing fields because it may
level off peaks and slow the response of the instrument. The filter also acts to quiet noise within the
instrument, making an additional digit of usable resolution available with the filter on in DC. The filter
function 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 will
appear.
Select With °®
Filter On ¡Off
Use the
s
or
t
keys to toggle between On and Off. Press the
Enter
key to accept the new setting.
Содержание Model 421
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