Stanford Research Systems SR844 User Manual page 86

3-28 Reference Section
Freq
This key displays the reference frequency. If the reference mode is EXTERNAL, then
the measured external reference frequency is displayed. Measurements are made 6–12
times a second and the display is updated at 5.7 Hz. The display will be erroneous if the
instrument is UNLOCKed or the frequency is OUT OF RANGE. Indicators on the front
panel show both of these error conditions. In external reference mode, the knob serves no
function with this display.
In INTERNAL reference mode, the internal reference frequency is displayed. The
internal reference frequency is adjusted using the knob. The SR844 offers 3 digits of
resolution in specifying the internal reference frequency, and 4 digits of accuracy. For
example, frequencies of 1.23 and 1.24 MHz may be selected. When 1.23 MHz is
selected, the actual reference frequency will be in the range 1.229 to 1.231 MHz.
Use PRECISE FREQ to display the frequency with more resolution (in either reference
mode).
PRECISE This key sequence shows the reference frequency with 6 or 7 digits of resolution using
FREQ the CH2 and Reference displays together. Read the two displays as if they were one
[Shift–Freq]
single display. The FREQ indicator within the CH2 display turns on whenever the
Precise Frequency is displayed.
To cancel this display mode, choose another reference display (Freq or Phase for
example).
While the internal reference frequency is set to 3 digits resolution, the actual frequency
generated in internal mode may be slightly different (within
I.F.
This key sequence shows the IF frequency on the Reference Display. See Chapter 2,
[Shift–
Sources of Error, for more information about the IF (chop frequency). This display is
AuxOut]
provided as a user convenience. The instrument has weak spurious responses at offsets
± ×
of 2
experiments to avoid specific IF frequencies.
When the reference is in internal mode and the IF frequency is displayed, the knob may
be used to adjust the internal reference frequency while showing the IF frequency.
Important!
The SR844 covers the operating frequency range in octaves bands. Users can check the
IF frequency to determine whether the instrument is at the high end of an octave band or
the low end of the next band. At the high end of an octave, the IF frequency will be close
to 3 kHz (12 kHz for time constants
kHz (8 kHz for time constants
for the analog CH1 and CH2 OUTPUTs. The fastest update rates occur at the high end
of each octave band (where the IF is the highest).
AuxOut This key shows the two rear panel Aux output values. Pressing AuxOut alternates
between AUX OUT 1 and AUX OUT 2. The selected output is indicated by AxOut1 or
AxOut2 within the display. The knob is used to adjust the selected output voltage within
the range
Phase
This key shows the phase, relative to the reference, currently being used for signal
detection. The phase is displayed in degrees (–179.99
adjust the phase. See below for more details.
SR844 RF Lock-In Amplifier
± ×
IF, 4 IF, etc. from the reference frequency. Some users may wish to set up their
≤
±
10.500 Volts.
≤ µ
300 s), while at the low end it will be close to 2
µ
300 s). The IF frequency affects the output update rate
°
to +180.00
±
1 in the 4th digit).
°
). The knob is used to