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OPERATION
RATE AND SAMPLES BUTTONS
SAMPLES
El
RATE
cJ"
0
3.51 Programming
Sampling
Rate
The RATE key is used to program either the sampling fre-
quency, or the time interval between individual
samples.
When programming
frequency, values between 1Hz and
IMHz may be entered. When entering frequency, the unit
will automatically adjust the frequency value to correspond
to the resolution
of the sampling
interval
(O.l@ec).
For rates abovc lOOkHz, the usable display resolution
is
reduced to 2% digits (although
4% digits are displayed)
because the A/D converter operates with S-bit resolution
above lDOkHz, or when
32,768 or more samples are
programmed.
When programming
time intervals, values between l@sec
and 1st~ may be entered. If a value below the allowable
resolution
(O.lpec)
is entered,
the
instrument
will
automatically
adjust the entered parameter to the closest
valid value.
The FREQiTIME
key can be -rsed when
entering
rate
parameters to toggle the instrument
between the time and
frequency
entry modes. The display will show the type
of units currently
in effect. When new data is being
entered, it will be entered in the same mode as the display
currently
shows unless FREQiTIME
has been pressed to
change to reciprocal units.
Example 1: Program a 35@ec sampling
interval.
1. Press RATE to allow entry of rate data. The display will
show the currently programmed value. For example, the
display might show:
50.00000 kHz
2. Press the FREQiTIME
key several times and note that
the display alternates between time and frequency. With
a 50kHz rate, the display
would
alternate
between
50kHz and 20~s~ because one value is the reciprocal
of the other (f = l/T).
3. Press: 3,5, ps to program the new value. The instrument
will then return to the previous
operating
mode.
Example 2: Program a 1OOkHz rate.
1. Press RATE to enter the rate entry mode. The unit will
then display the programmed
value.
2. Press FREQITIME,
if necessary, to display time inter-
val information.
If the instrument
is still programmed
with
the 35psec sampling
rate from Example 1, the
display will show:
28.57142 kHz
3. Press: 1, 0, 0, kHz
The new
rate will
be pro-
grammed,
and the instrument
will
return
to the
previous operating
mode.
Example 3: Automatic
recalculation
of frequency
units.
The resolution
of the programmed
sampling interval
is
O.lflec.
When entering
sampling
rate as a frequency,
however, it is quite possible for you to enter a frequency
parameter
that results in an interval
below the 0.1~~
resolution limit. For example, with a 35kHz sampling rate,
the resulting interval would be 28.57l@ec. In this instance,
the unit would adjust the frequency to result in the nearest
whole interval-28.6psec
in this case. Thus, if a value of
35kHz were entered, the unit would actually program a
value of 34.96503kHz.
1. Press the RATE key in order to enter the rate mode.
2. If necessary, press FREQiTIME
to place the instrument
in the frequency
entry mode.
3. Program a 35kHz rate with the following
sequence: 3,
5, kHz.
4. Note that the unit
adjusts the frequency
value to
34.96503kHz.
5. Press RATE and then FREQiTIME
to display sampling
interval. Note that a value of 28.6psec is programmed.
3.52 Programming
the Number
of Samples
The number of samples to take in a given measurement
sequence is programmed
through
use of the SAMPLES
key, as you might expect. The input parameter for this
mode may be entered either as the number of samples
(l-65,535), or as a time duration
for the measurement
se-
quence (0.65,534s). As is the case when entering sampl-
ing rate, the FREQiTIME
key is used to toggle the instru-
ment between these two modes. If you enter a time dura-
tion shorter than the programmed
sampling rate, the unit
will automatically
round the input to the nearest valid
value.
3-6
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