41
Subject to change without notice
Random sampling:
This sampling method enables time coefficients from 1µs/div
(sampling interval: 5ns) to 100ns/div. (sampling interval: 500ps),
which can‘t be realized with a maximum sampling rate of 100MSa/
s (sampling interval: 10ns) in realtime sampling mode. This allows
display of signals with higher frequencies as in realtime.
Random sampling assumes repetitive signals without any
change. The sampling is performed randomly, but with respect
to the trigger point. Under these circumstances, only one
sample is taken during a signal period. A complete signal
capture therefore requires a high number of signal periods,
until a complete signal (2048 samples) can be displayed and
therefore this takes time.
Under the influence of signal jitter, noise, phase or amplitude
changes, random sampling causes faulty signal displays.
Signals captured and stored in storage mode can be called via
the built-in RS232 interface for documentation purposes. For
further information please note section “RS232 Interface -
Remote Control”.
Signal display and recording modes
Signals can be recorded and displayed in six different modes:
REFRESH mode (“rfr” indicated by the readout)
ENVELOPE mode (“env” indicated by the readout)
AVERAGE mode (“avm” indicated by the readout)
SINGLE mode (“sgl” indicated by the readout)
ROLL mode (“rol” indicated by the readout)
XY mode (only the sampling rate is displayed by the readout;
top left position)
Except ROLL and XY mode, a signal recording in all other modes
requires a trigger signal.
In REFRESH, ENVELOPE and AVERAGE modes the instruments
behaves like an analog oscilloscope. The trigger circuit starts a
recording, overwriting the previous recording from the left to
the right side of the screen. After the recording has been
finished, the next trigger event starts the same procedure.
This can also be caused in automatic trigger mode without an
applied signal by the automatic circuitry. Then only the trace (Y-
POS. setting) is recorded.
In contrast to automatic trigger mode, in normal trigger
mode the automatic system is switched off and
consequently only a trigger signal can start a recording.
Unlike analog mode where the screen is dark until a trigger
signal starts the time base, in store mode the last recorded
signal remains visible as long as no new recording is
triggered by an input signal.
AVERAGE and ENVELOPE are REFRESH sub modes and
described in section “Controls and Readout” under item STOR.
MODE [41] [42].
SINGLE mode (“sgl”) enables the capture of one time events.
The recording is started by activating RESET (RES lit). After a
trigger event occurred and the recording is completed, the
RES LED extinguishes. SINGLE automatically switches over to
normal triggering, to avoid unwanted signal display caused by
the automatic trigger.
The Y-POS control can be used to shift the 0 Volt symbol
(
⊥
⊥⊥
⊥⊥
) to
the required graticule position. The trigger point symbol then
should be set above or below the 0 Volt position line, according
to the expected voltage of the event to be captured. Whether
the slope selection is set for a rising or falling slope depends
on the measurement task. After this procedure AC or DC input
coupling must be selected and the signal capture started after
pressing the RESET pushbutton.
For explanations regarding ROLL mode, please note this item
[41] (41.1.4) in section “Readout and Controls”.
Vertical resolution
The dot density in each operation mode is 8 bits = 28 = 256
dots displayed over a height of roughly 10 divisions. The
instrument is adjusted for 25 dots per division. This eases
processing and cursor measurement.
Insignificant differences between the (analog) screen display
and the (digital) data are unavoidable.
This concerns signal height as well as the position. The trace
position is defined in respect to the following horizontal
graticule lines:
Center line
= 10000000 (binary) = 80 (hex) = 128 (dec).
Top line
= 11100100 (binary) = E4 (hex) = 228 (dec).
Bottom line
= 00011100 (binary) = 1C (hex) = 28 (dec).
In contrast to analog mode with its theoretically unlimited resolution,
the vertical resolution has 25 possible trace positions per division.
If the signal is superimposed by noise or a critical Y-POS. setting
is used, the least significant bit (LSB) may change continuously.
This additionally reduces the vertical resolution in storage
mode, but is unavoidable. In contrast to the expensive flash A/
D converters used in this instrument, other converters such as
CCD cause more noise.
Horizontal resolution
The maximum number of signals to be displayed
simultaneously is three (2 channels in DUAL mode and a
reference or mathematic signal). Each signal consists of 2048
(211) byte (samples). Referred to the horizontal raster, the
resolution is 200 samples per division.
Pure (only) digital oscilloscope with VGA monitor type CRTs
offer only 50 samples per division. If LCD displays are used
the current resolution is 25 samples per division. For a given
time base setting the HAMEG instrument samples at a 4
(compared to VGA) or 8 ( referred to LCD) times higher sampling
rate. The higher number of samples/div results in a shorter
sampling interval. For the following example it must be kept in
mind, that the time base setting is related to the signal period
duration and consequently should enable the display of one
complete signal period. If e.g. a 50Hz signal has to be displayed
the time base should be set to 2ms/div. The maximum signal
frequency of a superimposed sine wave signal, which must
be sampled with at least 10 samples per period, depends on
the horizontal resolution:
samples/div sampling interval sampling rate max frequenc
200
2ms : 200 = 10µs
100kS/s
10kHz
50
2ms : 50 = 40µs
25kS/s 2.5kHz
25
2ms : 25 = 80µs
2.5kS/s
1.25kHz
Note:
1. The sampling interval is the time distance between two
samples. With low X
resolution the sampling interval
increases.
2. The sampling rate is the reciprocal value of the sampling
interval (1/sampling interval = sampling rate).
Adjustments
