3502
Optical Chopper System
23
that these signals will therefore only be as stable as the externally-controlled
chopping frequency.
To change the
Sync
source, press the
Sync
button until the LED under the desired
Sync
source lights.
Mode Button
The
Mode
button allows the User to change the frequency that F
outer
will lock to in
addition to the reference signals available at
OUT 1
and
OUT 2
(rear panel). The
table below gives the locking frequency of F
outer
and the reference signals
available at
OUT 1
and
OUT 2
, for each
Mode
setting.
In the table, the following definitions are used:
•
F
sync
: frequency of the
Sync
source
•
F
outer
: chopping frequency of outer slots as measured by IR sensor
•
F
inner
: chopping frequency of the inner slots; for single-slot wheels F
outer
is the chopping frequency, and F
inner
is undefined.
Mode Setting
F
outer
locked to
OUT 1
OUT 2
H/S
(H/S)
F
Sync
(H/S)
F
sync
[H/(7
S)]
F
sync
+/-
F
sync
F
outer
– F
inner
F
outer
+ F
inner
Normal
F
sync
5
F
sync
F
inner
Table 1: Chopping frequency and outputs vs. mode setting.
For all wheels with a dual slot pattern (except for the 60/2-slot wheel), F
outer
=
7/5·F
inner
. Therefore, F
outer
– F
inner
= 2/7·F
sync
and F
outer
+ F
inner
= 12/7·F
sync
.
When the
Sync
setting is
V
ext
, the reference signals available at
OUT 1
and
OUT 2
are
generated with respect to the measured chopping signal F
outer
.
Please see Table 2 on page 27 for a complete reference of output signals according
to
Mode
selection.
To change the
Mode
, push the
Mode
key until the LED under the desired selection
lights up.
Sync In
A TTL signal applied to the
Sync In
input will be used as a frequency and phase
reference in
EXT+
and
EXT-
modes. TTL pulses can be used to trigger the Chopper
Controller as long as they are longer than 1
s.