The DigikröM CM110/CM112 Monochromator is a versatile optical instrument designed for precise wavelength selection and manipulation in various spectroscopic applications. It functions as a single-channel monochromator, capable of isolating specific wavelengths of light from a broader spectrum. The device is controlled via an RS-232 serial interface, allowing for integration with computer systems and external control devices like the DK1201 handheld controller.
Function Description:
The core function of the CM110/CM112 is to separate light into its constituent wavelengths. This is achieved through a diffraction grating, which disperses incoming light. The monochromator then selects a narrow band of these dispersed wavelengths by means of an exit slit. The device can operate in both single and additive/subtractive dispersion modes (CM112 only), offering flexibility for different experimental setups.
The monochromator's operation involves several key commands:
- CALIBRATE: This command recalibrates the monochromator's position scaling factor and sets the zero position. It's crucial for accurate wavelength selection.
- ZERO: This command sets the grating angle by 0.0075 degrees in the clockwise direction, establishing a new zero offset.
- ECHO: Verifies communications with the CM110/112.
- GOTO: Moves the monochromator to a selected wavelength position. The wavelength can be specified in nanometers (nm).
- INC: Increments the zero offset value for machine #2 (CM112 only) by 0.0075 degrees in the counter-clockwise direction.
- ORDER: This command determines if the grating rotates clockwise or counter-clockwise.
- QUERY: Displays various monochromator status parameters, including current wavelength, grooves/mm, blaze, grating, scan speed, step size, number of gratings, and units.
- RESET: Resets the grating turret to the home position.
- SCAN: This command starts a monochromator scan between a START position and an END position at a determined rate.
- SELECT: Selects the grating that will be used.
- SIZE: Changes the step size, which affects the resolution and speed of wavelength changes.
- SPEED: Sets the speed at which the monochromator scans.
- STEP: Moves the monochromator by a preset amount defined by the SIZE command.
- TYPE: Induces the CM112 only, to change between additive and subtractive mode.
- UNITS: Selects the units for wavelength display and input (microns, nanometers, or angstroms).
The DK1201 Handheld Controller provides a user-friendly interface for controlling the monochromator without a PC. It features a keypad for numerical input and function keys for common operations like GOTO, SCAN, SLIT ADJ, FILTER, QUERY, RESET, CANCEL, and ENTER.
Important Technical Specifications:
- Wavelength Drive: Anti-backlash worm and wheel with microprocessor control. Bi-directional.
- Beam Path: Either right angle or straight through (standard configuration) from source.
- Design: Czerny-Turner, dual-grating turret.
- Focal Length: 110 mm.
- F/#: 3.9.
- Gratings: 30 – 3600 grooves/mm. The CM110/112 can accommodate two gratings on a turret.
- Wavelength Precision: >0.2 nm with 1200 g/mm grating.
- Wavelength Accuracy: >0.2 nm with 1200 g/mm grating.
- Slewing Speed: >100 nm/second with 1200 g/mm grating.
- Maximum Resolution: 0.2 nm with 1200 g/mm grating.
- Band pass: 0.1 nm with 1500nm slit and 1200 g/mm grating.
- Standard Slits (mm): 0.125, 0.15, 0.3, 0.6, 1.2, and 2.4.
- Software: Demo control program with source is included. A LabVIEW® Driver is available upon request.
- Interface: RS-232 standard.
- Power: 12VDC power supply.
- Warranty: One-year from delivery date.
- CE: Marked.
- Options: Hand-held control module for local control, IEEE-488 interface, Interface cables, GPIB to RS232 converter, Gold optics for IR range.
Wavelength Ranges: The CM110/112 is restricted to angles between 0 and 70 degrees. The upper restriction is imposed because the grating is almost edge-on to the incident beam beyond this angle. The manual provides a table of upper wavelength scan limits for different gratings (e.g., 3600 g/mm has an upper limit of 500 nm, 75 g/mm has an upper limit of 24000 nm).
Wavelength Scan/Slew Speeds: The actual scan speed of the monochromator is determined by the formula: Actual Speed = Maximum Speed / 2^n, where 'n' is a user-defined value. This allows for fine control over the scan rate.
Encoding/Decoding Data Bytes: The monochromator uses multi-byte specifiers for communication. Commands are sent as hexadecimal bytes, and responses are received similarly. The manual details the procedures for converting decimal values to hexadecimal and vice versa for proper communication.
Status Bytes: The CM110/112 responds with status bytes that indicate whether a command was accepted, if an error occurred, or if the monochromator is in a specific state (e.g., positive/negative orders, scan direction).
Novram Program: The monochromator has 128 memory locations (Novram) where various parameters are stored, including baud rate, current grating, zero offset values, calibration values, groove density, blaze, number of gratings, and units. These values can be read from and written to Novram.
Usage Features:
- Getting Started: The manual outlines the steps for verifying shipping contents, connecting hardware (power supply, RS232 cable), setting baud rate, and attaching a detector.
- Writing Your Own Control Program: The manual provides detailed command structures and examples for writing custom control programs using RS-232.
- Handheld Controller (DK1201): Instructions for using the DK1201 controller for various operations like GOTO, SCAN, OPTIONS (to adjust grating angle, current units, order, current type), and MANUAL (to calibrate wavelength, change zero offset, or increment/decrement).
- Error Screens: The manual describes common error messages such as "VALUE INVALID" and "COMPLETION ERROR" and how to address them.
- Queries: Provides a list of query commands and their purposes, allowing users to retrieve detailed information about the monochromator's current state.
- Option Commands: Explains how to use commands like GRATING, UNITS, ORDER, TYPE, and BAUDRATE to configure the monochromator's settings.
- Manual Commands: Details the MANUAL command for calibrating wavelength, changing zero offset, and incrementing/decrementing values.
- Product Conversions: Instructions are provided for changing slits, converting to a spectrograph, changing the optical path, and changing gratings. This highlights the modularity and adaptability of the device.
Maintenance Features:
- Calibrating with a Handheld Controller: Step-by-step instructions for calibrating the monochromator using the DK1201 controller, including setting the zero position and calibrating at a specific wavelength.
- Calibrating at a Wavelength with a Handheld Controller: Detailed procedure for wavelength calibration, ensuring accurate light selection.
- Installing the New Grating: This is a critical maintenance procedure. It involves carefully removing the monochromator cover, unscrewing and removing the PCB, detaching the old grating, installing the new grating, and then reassembling the device. A crucial warning is given: "THE SURFACE OF THE GRATING IS EXTREMELY DELICATE. IT IS NOT TO BE CLEANED EXCEPT BY USE OF INERT DUSTING GAS. ANY FINGERPRINTS ARE PERMANENT!" This emphasizes the need for extreme care during grating handling.
- Adjusting the Grating: After installing a new grating, it needs to be adjusted using a custom Allen wrench to ensure proper alignment.
- Shining a Visible Laser: A procedure involving a 633nm HeNe laser is described to adjust the laser beam to fall on the center of the collimating mirror, which is essential for optical alignment.
- Removing Power: Instructions for safely removing power from the monochromator and manually rotating the grating drive until the return laser beam is reflected back to the entrance beam on the collimating mirror. This is part of the grating adjustment process.
- Zero and Calibrate Offsets: After grating installation and adjustment, the zero and calibration offsets need to be reset and confirmed.
- Replacing PCB and Monochromator Cover: Final steps in grating installation, ensuring the device is properly sealed and protected.
The manual also includes reference drawings for the CM110/CM112 interface pin layout (for both AT 9-pin and PC 25-pin serial ports), optical bench mounting, CM110 dimensions, optical path design, and exit and entrance flange details, which are valuable for integration and troubleshooting.
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