SRS Labs SR540 Bedienungsanleitung
MODEL SR540
OPTICAL CHOPPER
MODEL SR540
OPTICAL CHOPPER
Copyright © 1986, 1988, 1995, 1997
Stanford Research Systems, Inc.
All Rights Reserved
Rev. 2.5 (03/2005)
Stanford Research Systems, Inc.
1290-D Reamwood Ave.
Sunnyvale, CA 94089 USA
(408) 744-9040
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TABLE OF CONTENTS
Symbols used ………………………………………………………...………. 2
Specifications ………………………………………………..………………. 3
Safety & Preparation for Use …………………………………..……….. 4
Quick Start Instructions ………………………………………………….. 5
Operating Instructions
Introduction ……………………………………………………………
6
Frequency of Operation ……………………………………………… 6
Changing Blades
……………………………………………………….
6
Baseplate Removal ……………………………………………………. 6
Applications
Single Beam …………………………………………………………... 7
Single Beam Chopping to 20 kHz …………………………………….. 8
Dual Beam Experiments ………………………………………………. 10
Detection at Sum & Difference Frequencies ………………………….. 11
Variable Aperture ……………………………………………………... 11
Calibration …………………………………………………………………… 12
Circuit Description
Motor Speed Control ………………………………………………….. 12
Optical Pick-Offs ……………………………………………………… 12
Frequency Synthesis …………………………………………………... 13
Frequency Display …………………………………………………….. 13
Power Supplies ………………………………………………………... 14
Parts List ……………………………………………………………………... 15
PC Layout …………………………...……………………………………….. 19
Schematic …………………………...………………………………………... 21
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SPECIFICATIONS
Chop Frequency 4 Hz to 400 Hz with 6 slot blade.
400 Hz to 3.7 kHz with 30 slot blade.
Frequency Stability 250 ppm/°C typical.
Long Term Frequency Drift < 2%, 100 Hz < f < 3700 Hz
Phase Jitter 0.2° rms from 50 Hz to 400 Hz.
0.5° rms from 400 Hz to 3.7 kHz.
Frequency Display 4 digit, 1 Hz resolution, 1 Hz accuracy.
Frequency Control 10 turn pot with 3 ranges:
4 Hz to 40 Hz
40 Hz to 400 Hz
400 Hz to 3.7 kHz
VCO 0 to 10 VDC. Control voltage overrides frequency dial.
Reference Modes Switch Left BNC Right BNC
up ƒinner ƒ
middle 5 x ƒ ƒ
down ƒ + ƒinner ƒ – ƒinner
Dimensions Controller 7.7" x 5.1" x 1.8"
Chopper Head 2.8" x 2.1" x 1.0"
Blade Diameter 4.00"
Power 100 / 120 / 220 / 240 VAC
50 / 60 Hz
12 Watts
Warranty Electronics - One year parts and labor on materials and
workmanship.
Chopper Motor - Ninety days parts and labor on materials and
workmanship.
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************ CAUTION ************
This instrument may be damaged if operated
with the LINE VOLTAGE SELECTOR set for
the wrong ac input-source voltage or if the
wrong fuse is installed.
LINE VOLTAGE SELECTION
The SR540 operates from a 100V, 120V, 220V,
or 240V nominal ac power source having a line
frequency of 50 or 60 Hz. Before connecting
the power cord to a power source, verify that the
LINE VOLTAGE SELECTOR card, located in
the rear panel fuse holder, is set so that the
correct ac input voltage value is visible
(figure 1).
To Change Voltage Selected: Open the cover on
the power entry module using a small
screwdriver; pull the voltage selector card
straight out using long-nose pliers; orient
selector card so that the desired voltage is
readable at the bottom; orient the indicator pin
to point up when desired voltage is readable at
the bottom (figure 2); insert voltage selector
card into housing, printed side facing left, and
edge containing desired voltage first; replace
cover and verify that the indicator pin shows the
desired voltage.
LINE FUSE
Verify that the correct line fuse is installed
before connecting the line cord. For 100V and
120V, use a 1/4 Amp fuse and for 220V and
240V, use a 1/8 Amp fuse.
LINE CORD
This instrument has a detachable, three-wire
power cord with a three-contact plug for
connection to both the power source and
protective ground. The protective ground
contact connects to the accessible metal parts of
the instrument. To prevent electrical shock,
always use a power source outlet that has a
properly grounded protective-ground contact.
OPERATE ONLY WITH COVERS IN
PLACE
To avoid personal injury, do not remove the
product covers or panels. Do not operate the
product without all covers and panels in place.
KEEP HANDS CLEAR OF CHOPPER
BLADE
SAFETY AND PREPARATION
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Quick Start Instructions
1. Make sure the correct line voltage is selected, the correct fuse is installed, and the power
switch is off.
2. Connect the chopper head to the controller with the supplied coiled cord.
3. Mount the 30 slot wheel for 400 Hz to 3.7 kHz or the 6 slot wheel for 4 Hz to 400 Hz,
and set the MAX FREQ/SLOT switch on the front panel for the desired frequency range.
4. Set the REFERENCE MODE switch 'up'. In this position the right BNC output is at ƒ,
the chop frequency of the outer row of slots; and the left BNC output is at ƒinner, the chop
frequency of the inner row of slots.
5. Connect the lock-in's reference input to the output that corresponds to the row of slots
that will be used.
6. Turn the power switch on and adjust the 10-turn dial for the desired chop frequency.
OPERATING INSTRUCTIONS
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INTRODUCTION
The Model SR540 Optical Chopper is used to
square-wave modulate the intensity of optical
signals. The unit can chop light sources at rates
from 4 Hz to 3.7 kHz. Versatile, low jitter
reference outputs provide the synchronizing
signals required for several operating modes:
single or dual beam; sum & difference
frequency; and synthesized chopping to 20 kHz.
FREQUENCY OF OPERATION
The choice of operating frequency is influenced
by several factors:
1. Avoid low frequency operation (below
100Hz). In general, phase jitter,
background noise and lock-in amplifier
noise all degrade at low frequencies.
2. Avoid high frequency operation. Motor
lifetime will be reduced if the unit is
operated for extended periods above
2KHz.
3. Avoid known noise frequencies. For
example, the line frequency and all its
even and odd harmonics should be
carefully avoided.
4. Avoid using the bottom 10% of the
frequency control dial. The phase jitter
of the reference outputs will degrade at
the low end of the range, so switch to the
next lower MAX FREQ / SLOTS range.
5. Always use the correct wheel as
indicated by the MAX FREQ / SLOTS
switch. Using the wrong wheel will
seriously degrade the performance of the
synthesized reference outputs (left
BNC). For frequencies from 4Hz to 400
Hz use the 6/5 slot blade; from 400Hz to
3.7kHz use the 30/25 slot blade.
CHANGING BLADES
The chopper blade (figure 4) may be replaced
by removing the three flat head screws, which
hold the outside hub to the wheel. When
replacing the blade, be sure to insert the blade
between the slotted optical detectors before
placing it on the wheel. Secure the blade by
sandwiching it between the wheel and outer
hub. Install and loosely tighten the three flat
head screws, which hold the hub to the wheel.
Then firmly tighten all three screws. Handle
blades carefully as they are easily bent.
BASEPLATE REMOVAL
The baseplate of the unit may be removed to
allow for pole mounting. Use an allen wrench to
remove the 6-32 bolt from the bottom of the
baseplate.
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