Description of the device

1. Connection with chopper head (through interconnecting cable)
2. Mains connector (12V)
3. Connection with chopper head (through interconnecting cable)
4. BNC connection (for external synchronization, 5V)
5. RS232 connection
6. USB 1.0. connection
7. Signalisation:
    1 power
    2 Rx transmission
    3 Tx transmission
8. Alphanumeric display
9. Numerical keyboard
10. [UP] button – change of frequency, selection of disc
11. [DOWN] button –  change of frequency, selection of disc
12. [OK] button – confirm settings, entering the frequency selection from the keyboard mode
13. [ESC] button, used for entering the disc selection mode
14. ¼ cal mounting (photographical) thread
15. Removable chopper disc

Purpose of the device

Optical chopper is a device used for a mechanical modulation of light beam. Slotted mechanical disc rotates thanks to a highly stabilized motor. Through the disc a light beam is passing and being modulated. The rotations are controlled with a usage of a dedicated controller connected with chopper head through a cable.

In case of any electrical or mechanical failures of the device or interconnecting cables, the device should be switched off, disconnected from mains, and repaired by a responsible and trained  person.

Technical parameters

Diameter of the disc (outermost) – 120 mm
Thickness of the head with a disc – 27 mm
Width of the slot (for disks with 2,4,8 slots) – 15 mm
Width of the slot (for disk with 16 slots) – 9.8 mm

Range of frequencies:
Disk with 2 slots: 0 Hz-150 Hz
Disk with 4 slots: 0 Hz-300 Hz
Disk with 8 slots: 0 Hz-600 Hz
Disk with 16 slots: 0 Hz-1000 Hz

The set contains

Chopping head
Controller unit
Interconecting cable (chopping head – controller unit)
Mains leads (220V ,50Hz)
Chopping disc (2 slots – 4, 8, 16 slots disc on request)

Start

Chopping head should be connected with a controller unit with an interconnecting cable. The interconnecting cable has special plugs which prevent from wrong connection.
To prevent from unwanted disconnection during the chopping action the screws at the plugs of the interconnecting cable should be used.
Chopper head with chopper disc should be stable fixed before the device is switched on.
The chopper head should be fixed with a ¼' thread (photographical standard) localised at the bottom of the chopper head.
The control unit is powered with a stabilized mains leads (delivered with the device).

Interface

Control unit is equipped with a numerical keyboard and a text display. Numerical keyboard is used to set precisely a rotation frequency.

Setting the disc kind

1. Press [ESC](13).
2. Pressing [UP](10) or [DOWN](11) set a number corresponding to a number of slots at the used chopper disc.
3. Accept with [OK] button(12).
4. The chopper will now recalculate and display the generated frequency.

Setting frequency

1. Press [OK](12).
2. With numerical keyboard (9) introduce the frequency. Example: to set 124.5 Hz, type the following numbers 01245 (remember to type 0 at the beginning, no „.” sign is used).
3. After last digit is introduced the disk should start the rotations (this could be not true if a rotation action was stopped with [1] button – see below – in this case [2] button should be pressed).

Fluent change of frequency

During rotation with [UP](10) and [DOWN](11) buttons a frequency could be changed fluently If a distance between present and required frequencies is too large, then the procedure described in „Setting frequency” section should be used.

Stopping rotation

To stop the rotations, during the rotation action button [1] should be pressed. On a control unit „STOPPED” will be displayed (caution – despite of this information, disk will be still rotating and fully stop after a while). To start the rotating action again (with the previous parameters) button [2] should be pressed - „RUNNING” will be displayed.

Restarting the rotation

Control unit remembers the settings done during last change.

Connection with a computer

Control unit could be connected with a computer with RS232 or USB. The control of disk rotation can be then performed with any computer terminal. After selecting serial port or USB a connection with a control unit should be established.

Frequency settings commands:
MSF - set frequency, 4 hex
MSR - run
MSH - hold  
MAF - ask about actual frequency 
MAL - check if a required frequency was achieved → status 0/1 
MAP - ask about programmed frequency
MAR – 0/1 - run status
MAS – 1-4 - shield
MAI – cr_opt_mod_1 - idtransmission speed: 19200,8,n,1

Connecting with an external device for synchronisation

Control unit is equiped with one BNC connector. The output standard is TTL 5V. Output sink current is 20mA

Exchange of a disk

To exchange a disk first screws at the inner disc ring should be unscrewed (screwdriver T6). Then the disk should be gently removed, and a new disk should be placed. The disk should be mounted in a position such that silver areas are placed at the head side. Screws should be tighten with a screwdriver.

Computer Software

A dedicated software with a friendly GUI is added. It allows to perform all operations on the chopper. Software works in Microsoft Windows and Linux environment. It is designed to automatically find all connected and switched on devices.

Installation:

1. Two versions of software delivered, located in the following directories:
 software/windows
 software/linux (tested for Ubuntu 11.04)
2. For older windows versions (xp) it is required to install FTDI VCP drivers (located in driver directory)
3. For Linux following libraries  should be available: Qt4 Core, Qt4 Gui, Qt4 Svg.
4. Software does not require to bi installed (can be run directly from CD or could be copied to computer, in the latter case full directories should be copied).

Running the software (see also the figure on the right):

(1) If a new device is attached while program is running, it is needed to perform new device scan.
(2) Display shows  actual frequency.
(3) Display shows programmed frequency.
(4) Diodes indicate if frequency is locked.
(5) Connection block allows to connect and disconnect device. Diodes indicate connection status.
(6) Drawing shows actually connected shield. When it is spinning means that modulator is running.
(7) Steering block allows to set frequency in allowed range, start and stop modulator.