Control of the Cairn Optoscan can be achieved using either the Optoscan microprocessor contoller, which provides all timing and control signals to the monochromator; or by direct PC control using an interface card. The microprocessor controller is an extremely powerful adjunct to the monochromator unit, which greatly simplifies its use. It allows the monochromator to either step between up to eight different wavelengths, or to perform complete spectral scans. The PC interface card will be of most interest to third party developers, where software is being used to synchronise multiple hardware devices and exact intervals between samples are less important.
Note that the microcontroller system INCLUDES the power supply for the monochromator unit, so a separate power supply is not required in this case. Please bear this in mind when comparing prices, as it effectively reduces the price of the microcontroller system by a useful amount. The power and convenience of the microcontroller system are such that we strongly encourage you to use it if you can, a particular benefit being the ability to control our popular range of photometry modules. To cater for the various possibilities the controller system is available in a number of versions, just as for our rotor control electronics.
Rack mounted Optoscan controller
The rack mounted microprocessor controller with integral keypad and display is our recommended controller configuration, designed for accurate timing with precise control over signal recording. The microcontroller we selected for it (Intel 80196) and the development system (MPE Forth) are specifically intended for precision timing operations, allowing us to control the monochromator with literally microsecond accuracy. Although we are happy to concede that this may be a slight overkill, we thought it was better be safe than sorry (and yes, there ARE some sorry systems out there....).
All monochromator functions can be controlled by the user via the keypad and display, with the ancillary electronics providing all the signals for controlling the monochromator. In particular, the microcontroller system allows our established range of photometry modules to be used with the monochromator, and it can also be controlled very easily by other equipment. The controller operates in two modes, namely stepping and scanning, with the ability to store up to four separate step and scan progams in memory. In wavelength stepping mode up to eight wavelength positions can be programmed, each with an independently selectable bandwidth and sampling time. Further control of the bandpass characteristic is possible by setting the input and exit slits to different bandwidths. Exploration of such possibilities is made very straightforward by the built-in lcd display, which can show a graphical representation of the bandpass characteristic for the chosen settings. Another tremendous advantage of the microcontroller system is that the relation between optical bandwidth and actual slit width is wavelength-dependent, and while this has to be taken into account when setting slit widths manually, the microcontroller software does this automatically, allowing the optical bandwidths to be specified directly.
Wavelength selection
Stepping between wavelengths can be controlled in a variety of ways. First, a programmed timing sequence can be entered, in which the monochromator spends an independently selected time at each wavelength, and the sequence can be repeated either indefinitely or for a specified number of times. Second, the monochromator can be made to go to any wavelength at any time, on receipt of appropriate external digital control signals. The protocol is exactly the same as for external control of the Optospin rotary filter changer, so software that has been written to control the Optospin in this way can also be used to control our monochromator. The external input and output facilities of the microcontroller system are too extensive to describe in any detail here, but please contact us for further information. Finally, for convenience when testing and setting up, the current wavelength position can be specified directly on the keypad.
The built-in lcd display and keypad can be mimicked by a PC via a null-modem (standard) serial cable. The 32-bit Windows programs that implements this terminal for various versions of the Optoscan are available from the downloads page. The controller can be supplied without the keypad and display on the system rack, and for these systems the PC terminal emulator is normal method of controlling the Optoscan.
Rack mounted controller options
The rack mounted system is available in two sizes. The single-height system has space for up to three standard modules, which will usually consist of a PMT amplifier, PMT supply and output module. For more than basic signal processing we provide a double-height version which can accomodate up to seven further standard width modules. The double height rack also has an built in metering facility to enable the signals on the internal lines to be read directly. This is particularly useful for adjusting background offsets accurately. In circumstances where the Optoscan will be programmed soley via the serial link, we can supply the system without the keypad and display.
Standalone Optoscan controller
The microprocessor controller can also be provided as a standalone unit. This option is likely to be of interest to those using the monochromator for imaging work, who do not require the facility for photometry measurements using our modular signal processing components. This is a simplified version of our rack mounted system controller, providing the same timing precision. It provides the same functionality for control of monochromator wavelength and bandwidth, being programmed via a front panel keypad and display. It does not contain the internal backplane circuitry, so has no facility for control of our photometry modules. As with the rack mounted controllers, the standalone unit can also be supplied without the keypad and display if it is intended to be programmed solely via the serial link.
PC card controller
This system is based around a PCI card which allows direct control wavelength control from a PC. It is likely to be of particular interest to third-party developers where the software is being used to synchronise multiple hardware devices (Such as CCD cameras in image acquisition systems). The system consists of the monochromator, a power unit with interface for the monochromator and a PCI controller card. We supply appropriate drivers with the system, together with a library of control routines which select the appropriate grating position and slit widths for a requested wavelength and bandwidth. The timing of the wavelength position and bandwidth changes are controlled entirely by the third party software and as such are dependent on the idiosyncrasies (and variabilities) of the operating system timing control. This system is designed for customers where software synchronisation is required and precise timing intervals between samples are less important.