New Focus 3501 Manuale utente
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Model 3501 User’s Manual
Optical Chopper
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2
Contents
351007 Rev. B
3
4
6
8
9
21
22
24
41
43
45
I Warranty
II Introduction
III Safety and
Preparation for Use
IV Quick Start
V Operation
VI Rack Mount Kit
VII Computer Control
VIII Command Summary
IX Troubleshooting
X AC Operating
Voltages
XI Specifications
Is a registered trademark of
New Focus, Inc.
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3
I
Warranty
New Focus, Inc. guarantees the chopper head to be free of defects for 90 days
from the date of shipment. All other parts of the Model 3501 Optical Chopper
are guaranteed to be free of defects for one year from the date of shipment.
This is in lieu of all other guarantees, expressed or implied, and does not
cover incidental or consequential loss.
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4
The Model 3501 Optical Chopper is designed to interrupt light paths in optical
experiments at frequencies from 4 Hz to 6.4 kHz. Both single and dual beam
experiments can be performed across a broad range of chopping frequencies.
The chopper has a crystal controlled frequency synthesizer that serves as an
internal reference frequency for locking the chopper to a particular chopping
frequency. Reference frequencies can also be provided through the Sync Input
to allow the chopper to lock to an external source. A block diagram of the
optical chopper system is shown in Figure 1.
Several measures ensure that jitter and drift of the chopping frequency is
reduced to a minimum. Precision photo-etched wheels are mounted on a
high quality DC motor. The motor head has a photo-sensor for monitoring
the chopping frequency of the outer part of the wheel (Fouter). The chopper
controller then actively stabilizes the motor speed to match the desired chop-
ping frequency. This technique minimizes phase noise at the chopping fre-
quency and provides for long-term stable chopping with a minimum of fre-
quency drift.
Figure 1 shows a block diagram of the Model 3501 Optical Chopper system.
Programmable divide/multiply circuitry allows for harmonic or subharmonic
locking of the chopper to the reference frequency. In addition, the phase of
the chopping frequency may be varied over a -180 to +179 degree range with
respect to the reference frequency. A variety of TTL level outputs are available
for use in triggering lock-in amplifiers, oscilloscopes, photon counters or box-
car averagers.
II
Introduction
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The chopping frequency, as well as a number of other operating parameters,
can be viewed on the front panel display, and cursor keys provide easy adjust-
ment of operating parameters. From the front panel the user can store and
recall up to nine instrument set-ups. An IEEE-488 interface provides remote
operation of all instrument functions.
The chopper head can be mounted on a 1/2”-diameter post or bolted directly
to a standard optical bench. The Model 3501 Optical Chopper is supplied with
four chopper wheels and a wheel cover. The Model 3510 Rack Mount Kit, an
accessory that is sold separately, enables the chopper controller to be mounted
in a rack (see Page 21).
Optical Trigger Motor
Chopping Head
Phase
Shifter
Ext V
4 Hz - 6.4 KHz
Micro-
processor
Front
Panel +/-
H/S
Norm
Out 1
Out 2
f Outer
f Synch
f Outer
Out 1
Out 2
Synch
Out
Int
Synch In Subharmonic
Divide by 1 to 15
Internal Frequency
Synthesizer
Harmonic
Multiplier 1 to 15
Motor
Controller
Divide by 7 Divide by 6
IEEE-488
Fig. 1
Block diagram of the Model 3501 Optical Chopper.
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Mounting the Chopper Head
The Model 3501 Optical Chopper head may be secured to standard optical
benches using 1/4-20 or M6 bolts. The bolts pass through the mounting plate
perpendicular to the plane of the optical bench. The chopper head can be
rotated off-axis by loosening the 1/4-20 set screws on the side of the motor
mount. Do not over-tighten the set screws.
The Model 3501 Optical Chopper head may also be mounted on standard
optical bench rods. First loosen the two 1/4-20 set screws which secure the
mounting plate to the head. Remove the mounting base. Insert the 1/4-20
knob (supplied with the chopper) into the base of the head. This knob is
inserted into the same hole occupied by the dowel on the mounting plate.
Slide the motor mount onto the optical bench rod and tighten the knob. Do
not over-tighten the knob.
Mounting the Wheel
Remove power from the control unit before attempting to change the chopper
wheel. Secure the chopper head to a work surface. Remove the four 4-40
screws that secure the retaining cap over the wheel, while taking care not to
bend the wheel. Install the replacement wheel, retaining cap and 4-40 screws.
Do not over-tighten the screws.
Control Cable
Connect the 6-wire cable from the connector at the side of the chopper head to
the MOTOR connector at the back of the control unit.
WARNING: Do not connect or disconnect the chopper head while the control
unit is powered or damage to components may occur. Always shut off the
instrument and allow the motor to stop before disconnecting the cable.
III
Safety and
Preparation
for Use
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Line Voltage Selection
The instrument may be damaged if operated with the line voltage selector set
at the wrong voltage or with the wrong fuses installed in the power entry
module. When the instrument ships from the factory, it will be programmed
for the standard AC voltage in the user’s country. To select a different operat-
ing voltage refer to the AC Operating Voltages section (Page 43).
Grounding
The line cord is a three-wire power cord for connection to the power mains
and a protective ground. The chassis is connected to the protective ground to
reduce the risk of electric shock. To avoid potential electrical shock, use only
mains that provide a protective ground.
Wheel Hazard
WARNING: The moving wheel may inflict injury. The operator should
assure the safety of personnel who may be exposed to this hazard.
Safety is important! The chopper wheel can cause injury if it is touched while
rotating. This is especially critical if you find yourself reaching into your opti-
cal set-up with the lights off. You may want to use the chopper wheel cover to
reduce the chance of injury.
Environment
The Model 3501 Optical Chopper may be operated in an ambient of 0 to 40
degrees C. It is recommended to avoid direct sunlight on the LED display.
WARNING: Hazardous voltages, capable of causing death, are present inside
this instrument. Do not operate the instrument with the covers removed.
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Before operating the Model 3501 Optical Chopper, please review the previous
section to make sure the chopper is ready for use.
1. Mount the chopper head securely on an optical bench.
2. Mount the 42/30 wheel on the head. Avoid bending the wheel. The wheel
should be free to turn without contact to the optical sensor or nearby
equipment.
3. Connect the cable between the chopper head and the connector marked
MOTOR on the back panel of the control unit.
4. Check that the correct line voltage has been selected and the proper fuse
inserted into the mains power entry module at the back panel of the con-
trol unit. Connect the instrument to the power mains.
5. After insuring the safety of nearby personnel, switch on the instrument.
6. Recall instrument set-up “0” (factory default setting). Press SET until
“RECALL” is lit. Press the up/down arrow keys until “0” appears in the
display window. Press the left or right arrow key to recall set-up “0”.
7. The instrument will lock at 84 Hz within 1 minute.
8. To choose a particular chopping frequency, press the Set key until the
FREQ LED is lit, and then use the up/down arrows keys to adjust the
chopping frequency.
IV
Quick Start
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This section describes operation of the chopper, starting with an overview of
the front panel functions. This is followed by a description of the chopper
back panel and the chopper head.
V
Operation
Sync
Input
Wheel Sync
Measure
Set Power
Mode
Synthesizer
Output F Outer
60
42/30
7/5
2
V ext.
EXT
+
EXT
-
INT
SYNC IN
F outer
OUT 1
OUT 2
UNLCK
DEG
kHz
Hz
ACT
FREQ
PHASE
H
S
RECALL
STORE
IEEE
H/S
+
/
-
NORMAL
NEW FOCUS, Inc.
Made in USA
3501 Optical Chopper
Fig. 2
Front panel of the Model 3501 chopper controller.
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