Stanford Research Systems SR865A, Руководство по эксплуатации

Страница: 49 / 221

Chapter 1 Getting Started 31
SR865A DSP Lock-in Amplifier
4. Let’s leave the Scan Parameter at internal
reference frequency.
Touch {Begin Value} to highlight the start
frequency. Enter 99.990 kHz.
Touch {End Value} to highlight the stop
frequency. Enter 100.010 kHz.
Let’s scan a 20 Hz span around the signal
frequency (100.000 kHz).
This setup will increase the internal frequency
from 99.990 kHz to 100.010 kHz. To reverse
the scan, simply reverse the begin and end
values.
5. Touch {End Mode} once to select Repeat. This will repeat the scan over and over jumping
from the end value back to the begin value at
the end of each scan.
6. Touch {Close} to return to the Trend Graphs. The lock-in frequency has not been changed,
we have only configured a scan. The scan has
not been started.
7. Press [Scan/ setup ] briefly (don’t hold it) to turn
on the scan.
The
Ready
LED turns on indicating that the
scan is ready (at the start value). In this case,
the internal frequency (in the info bar at the top)
is shown in orange indicating that it is under
scan control. At this time, the frequency is the
start value or 99.9900 kHz.
8. Press [Play Pause/ reset ] briefly (don’t hold it) to
start the scan.
The Run LED turns on indicating that the scan
is running.
The internal frequency starts scanning up. The
current value is shown in orange in the info bar.
When the end value is reached, the scan resets
to the beginning value and repeats.
The trend graphs show a resonance as the
internal frequency passes through 100.000 kHz.
This is because the difference between the f
signal
and f
internal
gets slower as the f
internal
approaches
f
signal
and then gets faster after it passes f
signal
.
The time constant attenuates this difference
frequency when it is large.
9. Press [Screen Layout] once to show the full
screen strip chart.
Touch the white scale tile {Time} to display the
horizontal scale palette (bottom right of screen).
Touch repeatedly to zoom out to 10 S/div.
It is much easier to visualize a scan using the
strip charts since the chart time scale can be
matched to the scan time.
This scan takes 1m40s or 100 s so a chart span
of 100 s will display an entire scan.