Agilent Technologies DP111 - Manual (Page 38)

User Manual: Agilent Acqiris 8-bit Digitizers Page 38 of 59
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4.2.7. Acquisition Mode
The acquisition mode of the digitizers is selected using one of four
acquisition mode buttons in the Acquisition section of the control panel.
Available acquisition modes are Auto, Normal, Single and Stop
This Acquisition section of the control panel also indicates the number of
waveforms acquired per second by the digitizer. The use of each of the acquisition modes is described below. In the
discussion, a valid trigger indicates a trigger signal meeting the trigger conditions at a time when the digitizer is
armed and ready to acquire data. In Single and Normal modes the display will only be updated after each active
digitizer has received a trigger.
Stop will stop the acquisition and hold the latest complete acquisition on the display.
Single mode is used in order to capture one event at the first valid trigger. It freezes the acquisition in the digitizer’s
memory, and on the display, until the user requests another acquisition. After an acquisition is taken in Single mode,
the digitizer will ignore subsequent trigger events until the Single button is pressed again or another acquisition mode
is selected. Pressing the single button re-arms the trigger and captures one acquisition at the next valid trigger.
Normal mode is used to continuously acquire waveforms into memory for valid trigger events. The display is
updated with the new acquisitions in accordance with the Display Refresh Rate setting under the Options menu on
the top line of the AcqirisLive Control window. Acquisitions will happen for each valid trigger until either single or
Stop is pressed.
If the trigger indicator at the lower left of the waveform display does not blink green, the digitizer is not receiving
valid triggers. Check the trigger settings or select Auto mode in order to obtain a display of the waveform.
Auto mode will acquire and display waveforms according to the trigger settings if a valid trigger is present within a
timeout interval. If a valid trigger is not available within this interval, the digitizer generates its own trigger in order
to digitize and display whatever signal is at the input at that time.
If valid triggers are received at a high enough rate, Auto mode behavior differs little from normal mode behavior on
the display. However if the trigger rate is too low or trigger settings are not appropriate for the characteristics of the
signal, the input signal will not be stable on the display. This occurs because the internal auto-trigger generated by
the digitizer is asynchronous to the input signal.
Auto mode is often used to aid in setup when the input signal must be quickly characterized in order to determine
proper trigger settings for Normal or Single mode acquisitions.
4.2.8. Timebase and Memory
The timebase and memory settings should be chosen together
in order to optimize the desired sample rate for the acquisition.
In Oscilloscope Mode the timebase settings range from
10 ns/div to 5 S/div. In Transient Recorder Mode time
windows of 100 ns to 20 Ks are available when using a card
with the 2 Mpoint memory option.
In order to change the timebase click on the white area
in the timebase display window and select the desired
timebase from the list. Alternatively, the Decrement /
Increment timebase selection buttons may be used in order to change the timebase in steps with each click of the
mouse. The sample rate and sample interval resulting from the combination of memory and timebase are indicated
under the Sampling section of the control panel.
The Memory setting shows the maximum number of points to be acquired. The actual number of points acquired
could be less than the maximum number set if the acquisition time window selected fills less than the selected
amount of memory at the full sample rate. Alternatively, in Oscilloscope Mode, if a slower timebase is selected, in
order to ensure that the selected amount of memory will be filled before the acquisition is complete, the digitizer will
reduce its sample rate as necessary. This action differs from the same case in Transient Recorder Mode where
preference is given to the selected sample interval.
In Transient Recorder Mode, the digitizer will continue to allocate more memory with increasing capture times. This
is done in order to maintain the selected sample interval for as long a time window as is possible given the available
memory. When the card memory is fully utilized, the sample rate will decrease with increasing capture times.