THORLABS MC1000 User manual

Doc 1693-D03 Revision B 6/6/00
MC1000
MC1000MC1000
MC1000
Opto
OptoOpto
Opto-
--
-Mechanical Chopper
Mechanical ChopperMechanical Chopper
Mechanical Chopper
Operating Manual
THORLABS, Inc. Ph: [phone]
435 Route 206N Fax: [phone]
Newton, NJ 07860 USA www.thorlabs.com
PHASE ADJ
EXT EN
REF OUT
EXT REF IN
ENTER
CYCLE
FRE
Q
DOWN
FREQ UP
SETUP
RECALL
FREQUENCY
REF
SELECT
D
SE
T
N
SET
SETUP
SAVE MODE
PWR
MODEL MC1000 OPTICAL CHOPPE
R

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Table of Contents
TABLE OF CONTENTS 2
GETTING STARTED QUICKLY 3
Setup 3
Internal Reference Operating Mode 3
External Reference Mode 3
SECTION 1.0 OVERVIEW 4
SECTION 2.0 DESCRIPTION 5
Optical Head 5
Controller Front Panel Features 6
Controller Rear Panel Features 8
SECTION 3.0 OPERATING INSTRUCTIONS 9
Internal Frequency Synthesizer 9
Setup for Internal Reference Frequency 9
Selecting the REFERENCE OUT signal 9
Why doesn’t the motor speed exactly match the set speed ? 9
External Reference Mode 10
Setup for External Reference Frequency 10
Selecting the REFERENCE OUT signal 10
Harmonic Reference Generation 10
Setting the Reference Harmonic 10
Setting the Sub-Harmonic 11
Combining the Harmonic and Sub-Harmonic Modes 11
2-Frequency Chopping 11
Setting the Chopping Speed in the 2-Frequency Mode 11
Setting the Chopper Blade 11
Adjusting the Chopper Phase 12
Phase Adjustment-Related Stability Issues 12
SECTION 4.0 SERIAL INTERFACE 13
Serial Port Pin Outs 13
Serial Port Parameters 13
Serial Interface Command Screen 13
Serial Command Summary 14
SECTION 5.0 SPECIFICATIONS 15
SECTION 6.0 MAINTENANCE & TROUBLESHOOTING 16
Setting the Line voltage 16
Fuse Replacement 16
Cleaning 16
Diagnostic Messages 16
Technical Support 16

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Getting Started Quickly
This section is provided for those interested in getting the MC1000 up and running quickly as a basic optical
chopper. The more advanced features are described in detail in the following sections.
Setup
•Carefully unpack the MC1000 controller, optical head, and accessories. If any of the items appear damaged,
do not use the MC1000. Call Thorlabs and arrange for a replacement .
•Remove the 3 mounting screws and lock washers from the chopper blade hub using the 1/16” hex key
(provided).
•Unpack the 10-slot blade and install onto chopper blade hub using the 3 screws and washers removed in the
previous step. Tighten the screws securely with the hex wrench.
•Attach the modular cord into jack labeled OPTICAL HEAD on the back of the MC1000 controller and plug the
other end into modular jack on the optical head.
•Mount the optical head on a sturday surface and check that the blade can spin free of any obstruction.
•Attach the AC line cord to the MC1000 and plug into a AC outlet.
Note: the MC1000 can be operated from 100-120VAC or 220-240VAC. A voltage selector switch is located inside
of the MC1000 controller. If you are not sure what operating voltage your unit is set to, proceed immediately to
Section 6.0 for instructions on setting the operating voltage.
Internal Reference Operating Mode
This MC1000 is most commonly used in the internal reference mode. The chopping speed is set by the internal
crystal-stabilized frequency synthesizer.
•Turn the MC1000 power on. The LED display will go through a startup sequence: first, all of the display
segments and LEDs are lit, then the firmware rev level is displayed, then the current blade setting is displayed.
•The display should show “b 10” for the 10-slot blade. If not, press the FREQ UP button until the “b 10” message
is displayed and then release the button. The unit will time out after a second or two and go into a standby
mode with the display showing “oFF”. If you miss the timing of this, turn the power switch off then back on again
to return to this mode.
•If the unit comes up in the EXTERNAL REFERENCE Mode (as indicated by the LED above the EXT EN key
being lit), press the EXT EN key to turn it off and return to the internal reference mode.
•The unit should be in a standby mode with “oFF” displayed on the front panel. Press any of the keys to start the
chopper motor.
•To change the chopper speed, press the FREQ UP or FREQ DOWN key until the desired speed is shown.
Release the key an the unit will adjust its speed and lock onto the set speed within a few seconds.
External Reference Mode
This mode is very similar to the internal reference mode except that the chopper blade is locked to a logic-level
external reference signal.
•To enable external reference mode, attach a TTL or CMOS logic level reference signal to the EXT REF BNC
on the front panel and follow the above steps.
•Press the EXT EN key to enable the external reference mode.
Note: If the chopper does not lock to the exactly frequency of the external signal check that the harmonic multiplier,
N, is set to 1 by pressing the MODE key until the light under the SET N LED is lit. The display should show a 1. If
not, press the FREQ DOWN key until it reaches 1. Repeat his step for the sub-harmonic divider, D.

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Section 1.0 Overview
The MC1000 Optical Chopper is a precision instrument utilizing advanced features to meet the most demanding
applications. The MC1000 uses a phased-lock loop (PLL) motor speed control design to precisely lock the
chopping speed and phase to a reference signal. An internal, crystal-stabilized frequency synthesizer provides an
accurate and stable reference frequency for ultra-low long-term frequency drift.
Unlike conventional, open-loop speed control designs, the PLL speed control circuit also allows the MC1000
chopper to be synchronized to external reference signals, including other MC1000 choppers and reference sources
such as DSP lock-in amplifiers. The phase of the MC1000 chopper wheel is continuously adjustable from -πto +π
(-180°to +180°).
For more advanced measurements, the MC1000 can lock to a harmonic, sub-harmonic, or fractional-harmonic of
an external reference frequency. A second PLL circuit is used to multiply the external reference up to the 15th
harmonic. This multiplier is followed by a digital divider to divide the reference down to the 15th sub-harmonic. By
combining both the frequency multiplication and division together, a fractional harmonic can be obtained.
The MC1000 also supports 2-frequency chopping from a single chopper blade. A special blade is available with 7
outer slots and 5 inner slots. This slot combination allows a single beam to be split and individually modulated for
ratiometric experiments. Other applications include pump-probe experiments where the pump beam is modulated
at the outer frequency while modulating a probe beam at the inner frequency. The MC1000 provides the sum and
difference frequencies of the 2-frequency blade for accurate lock-in detection of the frequency-mixed response.
The precision, photo-etched chopper optical wheel is driven by a high-quality, Swiss-made rare earth magnet DC
motor. The compact optical head has a wide base for extra stability. The base is slotted for two ¼-20 mounting
screws on 2” centers. The interface cable uses standard RJ-45 modular connectors for easy setup.
The MC1000 controller includes a large, 4-digit, easy to read LED display for monitoring the chopper frequency. All
of the chopper operating modes are accessible from streamlined, front panel push-button controls. Multiple user
setups can be easily saved and recalled from non-volatile memory. An RS-232 serial interface is included as a
standard feature for remote interfacing the MC1000 to other equipment.
Thorlabs offers a number of different blades to extend the range of the chopping frequency. A standard 10-slot
blade is included with the MC1000. 15 slot, 30 slot, and the 2-frequency blade.

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Section 2.0 Description
Optical Head
The optical head consists of a precision photo-etched chopper wheel, a high-quality Swiss DC motor, a machined
aluminum housing, and the photo-interrupter motion detection electronics. The key features of the chopper head
are highlighted in Figure 1.
Figure 1. Optical Head Features
Feature Description
1 Precision Chopper Blade (available in 10, 15, 30 slots, and a 7:5 2-frequency)
2 1/16” Hex Mounting Screws and lock washers (qty 3)
3 Photo-interrupter Speed Sensor
4 Blade Hub
5 Modular Interface Connector
6 Mounting Base

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Controller Front Panel Features
Figure 2. Front Panel
Feature Description
1 4-Digit LED Display (to display operating frequency and user messages)
2 FREQ UP / CYCLE Key - This key is used to increase the chopping frequency when operating in
the internal reference mode. It is also used for cycling through input options for other operating
modes.
3 FREQ DOWN / ENTER Key - This key is used to decrease the chopping frequency when
operating in the internal reference mode. It is also used for as an enter key when setting the
various operating parameters.
4 PWR button - Press in to power the MC1000 on.
5 MODE - Pressing this key cycles through the various input modes (REF SELECT, SET N, SET D,
RECALL and SAVE). The currently active mode is indicated by the LED above the legend. Note:
the available input modes are dependent on the operating state (i.e. the SET N and SET D are
not active when operating in the internal reference mode).
6 SAVE SETUP - When this LED is lit, the user can save the current configuration to one of five
setups. Use the FREQ UP / CYCLE key to select the setup number and press the FREQ DOWN /
ENTER to save the setup to that number. To avoid Note, the setup number will wrap around back
to 1 after it reaches 5 when pressing the FREQ UP / CYCLE key.
Also, the setup will be saved to the displayed setup number by default if a short timeout period
expires. If this is not desired, press the MODE key to escape out of the SAVE SETUP mode.
MODEL MC1000 OPTICAL CHOPPER
REF SET
D
SET
NRECALL SETUP SAVE SETUP
EXT REF IN
REF OUT
EXT EN
FREQ UP
CYCLE
FREQ DOWN
ENTER
MODE
FREQUENCY (Hz)
PWR
PHASE ADJ SELECT

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7 RECALL SETUP - In this mode, the user can recall one of the five user setups. Select the setup
number with the FREQ UP / CYCLE key and press the FREQ DOWN / ENTER to restore the
saved configuration.
8 SET D - This mode allows the user to select a sub-harmonic of the external reference input. The
external reference frequency will be divided by this value and used to synchronize the chopper
blade. The sub-harmonic can be used with the harmonic multiplier, N, to create fractional
harmonics (i.e. chopper frequency, fchopper = REFEXT * N / D).
Note: The Harmonic, N, and sub-harmonic, D are only available when using the external
reference input and a single frequency chopping blade (i.e. 10, 15, or 30 slot blade).
9 SET N - This mode allows the user to select a harmonic of the external reference input. The
external reference frequency will be multiplied by this value and used to synchronize the chopper
blade. The harmonic multiplier can be used with the sub-harmonic divider, D, to create fractional
harmonics (i.e. chopper frequency, fchopper = REFEXT * N / D).
10 REF SELECT - This key allows the REF OUT signal to be selected from a number of sources
depending on the operating mode selected.
Operating Mode Available sync sources
Internal Reference Mode: OUT, SYN
External Reference: OUT
2-Frequency Blade: OUT, SYN, SUM, DIFF
Where: OUT = chopper wheel frequency (for the 2-frequency blade, the outer blade frequency)
SYN = the internal frequency synthesizer (or the harmonic generator for the external
mode)
SUM = sum frequency for the 2 frequency blade
DIFF = difference frequency for the 2 frequency blade
11 PHASE ADJ - a 12-turn pot to continuously adjust the chopper wheel phase from -πto +π.
12 REF OUT - the reference output signal selected by the REF SELECT mode (CMOS logic level).
13 EXT REF IN - the external reference signal is connected to this input BNC (TTL / CMOS logic
level).
14 EXT EN - Pressing this key toggles the MC1000 between the internal and external reference
mode. When the unit is in the external reference mode, the LED next to this key is lit.

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Controller Rear Panel Features
Figure 3. Rear Panel
Feature Description
1 RS-232 Serial Port Connector
2 Modular interface connector for the optical head
3 Cooling fan
4 AC input and fuse receptacle
OPTICAL HEAD
RS-232
Manufactured by
230VAC 50-60Hz
115VAC 50-60Hz
POWER 10W MAX.
125mA Type T FUSE
250mA Type T FUSE
Newton, NJ USA

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Section 3.0 Operating Instructions
Internal Frequency Synthesizer
The MC1000 is most frequently used in this mode where the chopper wheel frequency is locked to an internal
crystal stabilized frequency reference. The PLL motor speed control circuit maintains a precise lock to the
frequency and phase of the internal reference frequency creating an ultra-stable chopping signal. The chopper
wheel phase can be contiuously adjusted.
Setup for Internal Reference Frequency
1. Follow the setup procedures in Getting Started Quickly section.
2. Turn the MC1000 power on.
3. If the EXT EN LED is lit, press the under the LED to return the unit to the internal frequency mode.
4. Set the chopper operating speed as desired using the FREQ UP or FREQ DOWN keys. While holding down
these keys, the set speed will be displayed but the motor speed will not change until the key is released.
5. After releasing the keys, the chopper should adjust its speed and lock onto the reference within a few seconds
as indicated by the chopper speed shown on the digital display.
Selecting the REFERENCE OUT signal
In the internal frequency mode, the reference output signal can be set to the actual chopper wheel frequency or the
internal frequency synthesizer. In most cases, such as when selecting a reference for a lock-in amplifier, the
chopper wheel frequency will be used since it provides a direct measurement of the chopper phase and frequency.
The chopper wheel reference is derived from a photo-interrupter on the optical head that senses the motion of the
chopper blade.
The internal frequency synthesizer has slightly less phase jitter than the chopper wheel reference since it is not
effected by external disturbances. Therefore, there may be cases where using the internal synthesizer as the
reference output yields better performance (i.e. when synchronizing multiple choppers).
1. Press the MODE key until the REF SELECT LED is lit.
2. Press the FREQ UP / CYCLE key repeatedly until the desired reference output signal is shown. Once the key
is released, the selected reference signal will be routed to the front panel BNC labeled REF OUT.
Note: the display prompt for the direct chopper wheel frequency is ‘OUT’. The internal synthesizer display prompt is
‘SYN’.
Why doesn’t the motor speed exactly match the set speed ?
The MC1000 internal frequency synthesizer uses a 1.000MHz crystal oscillator which is divided down by a 32-bit
digital divider to generate the reference signal to lock the chopper wheel to. The MC1000 microprocessor uses an
advanced algorithm to match the set speed as closely as possible. However, there are some frequencies that
cannot be achieved exactly. This is due to the limitations of dividing the 1.000MHz clock by an 32-bit integer divisor,
and does not effect the stability of the chopper frequency.

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0
External Reference Mode
A major benefit of using a PLL circuit to control the chopper wheel speed is that the chopper can be locked
precisely to an external reference signal. This allows the MC1000 to be used in advanced setups, for example,
multiple MC1000 choppers can be synchronized to a single reference signal, or master-slave combinations where
one chopper is the master reference and a second chopper is slaved off the reference output of the first. The latter
example provides a convenient way to measure long decay time fluorescence and other similar types of
experiments.
The MC1000 will accept a TTL or CMOS logic level input as an external reference. The advanced PLL design used
in the MC1000 even accepts reference signals that do not have a 50% duty cycle. A special feature of the external
reference mode, locking to harmonics and sub-harmonics of the reference signal, is describe in the following
section.
Note: Having an active external reference attached to the EXT REF IN during MC1000 power up may cause the
unit to lock up. If this occurs, remove the external reference connection, and recycle the power. When the unit
finishes its startup sequence, attach the external reference signal.
Setup for External Reference Frequency
1. Follow the setup procedures in Getting Started Quickly section.
2. Turn the MC1000 power on.
3. If the EXT EN LED is not lit, press the key under the LED until it lights indicating that the unit is in the external
reference mode.
4. To have the chopper lock to the fundamental of the external reference frequency (i.e. the chopper speed will
equal the external reference frequency, the harmonic multiplier, N, and the sub-harmonic divider, D, must each
be set to 1. The check these values, use the MODE key to select the N and D parameters and adjust their
values as necessary.
5. The chopper should adjust its speed and lock onto the reference within a few seconds as indicated by the
chopper speed shown on the digital display.
Selecting the REFERENCE OUT signal
In the external frequency mode, the only signal available for the reference output signal is the actual chopper wheel
frequency. The controller will not allow the REF SELECT option to be changed.
Harmonic Reference Generation
Harmonic generation is a special feature available when operating in the external reference mode. The MC1000
uses a second PLL circuit to multiply the external reference frequency from 1 to 15 to generate up to the 15th
harmonic. The PLL is then followed by a digital divider which can be programmed from 1 to 15 to divide the
reference frequency and create sub-harmonics. Additionally, both the harmonic, and sub-harmonic modes can be
used to create fractional reference frequencies. The new frequency is used as the chopper reference for chopping
at a variety of frequency combinations, all derived from the external reference.
Note: Harmonic and sub-harmonic modes are not availble when using 2-frequency blades.
Setting the Reference Harmonic
1. Press the MODE key until the SET N LED is lit. The current value for N is displayed. Use the FREQ UP /
CYCLE key to select the desired harmonic. The display will wrap around to 1 after it reaches 15.
2. Once the FREQ UP key is released, the MC1000 will apply the reference signal to the multiplier circuit and the
reference frequency will increase to N * fEXT REF. If the harmonic frequency exceeds the maximum chopping