| TRISTAN® Spectrometer
The optic Cell As wide spectral regions are analysed with spectral devices, they may have no or only slight colour aberrations. Reflecting components are preferred for this reason. As a consequence, the ray path must be folded. The beams hit the elements under an angle. This causes image errors, e.g. astigmatism and coma. These image errors lead to an inferior resolution and less efficiency. However, these image errors can only be minimised with a suitable layout. The optic cell in TRISTAN® is an asymmetric Czerny-Turner construction. It provides the option to freely select the focal length and angle of the mirrors. This minimises the coma error, which occurs with all spectrometers.
The irradiation to be measured is coupled into the cell via an SMA fiber plug through a gap.The first mirror merely serves to deflect the beam onto another mirror, which is designed to minimise the coma with its position and focal length. It collimates the beam and deflects it onto an optical grid, whose efficiency is optimised for the specific wavelength range. Here the spectrum of the beam is broadened, reflected and projected onto the optic sensor via a focus mirror.
The sensor picks up the spectrally split irradiation and converts it to an analog electric signal. Different sensors are used for detection depending on the spectral range. There are also additional screens between the individual elements to minimise diffused light. The clearance on the spectrometer's right side serves to fade out the zero diffraction order.
When measuring UV light, which is scattered more on rough surfaces, highly polished optics have to be applied in the spectrometer to keep the scattered light fraction as low as possible.
On-board Intelligence A 32 Bit RISC processor as well as the supplied firmware let the spectrometers of the TRISTAN® 5and TRISTAN® light series perform measurements independently and process export the results under consideration of all device-specific parameters like dark current compensation and amplitude correction and then export these results as usable measuring results via interfaces. Additional data processing on the PC is not necessary. In addition, the TRISTAN® spectrometers can be easily integrated in the client's software environment.
All devices are equipped with functions for signal processing. These are described in the following.
The number of AddCycles stands for the number of measurements (at most 100) for deriving and mapping a mean value. With manual exposure time, each measurement is performed with the set time. This minimises noise and visualises signals, whose amplitude corresponds to the noise of a single measuring operation. Increasing the AddCycles also increases the measuring time and should be used for weak signals.
The iterations function is a multiple measurement with varying exposure times. At most 8 iteration steps are possible, which are merged to a measuring curve. This way, both strong and weak signals are measured with the optimum exposure time. Short exposure times are used for the strong signals, while weaker signals are extracted from the noise with longer exposure times and therefore displayed more clearly. This function allows the simultaneous display of weak and strong signals. The dynamic range of the TRISTAN® spectrometer can be increased to a factor of 128 maximum.
Max. Cycle Time This time indicates the maximum duration of one measuring operation.
Exposure time The exposure time indicates the time in which the detector is exposed to light. This time is not endless but limited by the saturation of the detector and the dark current. The exposure times of the applied Back Thinned detector are between 3 ms to 16 s. Automatic Exposure If the automatic exposure function is set, the TRISTAN® automatically selects the best exposure time up to the maximum value. This prevents that the signal becomes saturated and displays it optimally. The maximum exposure time is defined by the max. cycle time.
Noise Filter This uses the fact that there is no amplitude difference higher than 33% between pixels, because steep signals also have a Gaussian progression.
In case of a greater divergence, the difference is recalculated to a meaningful value. This excludes spikes from the calculation, which cannot be present, and the signal is cleared of noise at the same time with this function. This function should always be activated, because it improves the signal quality without "diffusing" it.
The only exceptions are the NIR devices, where the detectors are used with a relatively low pixel count. This may lead to a loss of signal information.
The Gaussian filter is a smoothing function for the curves. A Gaussian function is applied on each pixel mathematically. The value in nm to be entered corresponds to ∆2σ of the Gaussian curve. The curve becomes smoother with increasing ∆2σ.
Important: This function may lead to signal information loss! A meaningful value corresponds to the optical resolution of the spectrometer.
The device-specific parameters are saved in the device and also considered during measuring. These are described in more detail in the following.
Amplitude Correction The sensitivity of silicon detectors varies for each wavelength. In the VIS range, these are very sensitive but strongly decrease in the UV and NIR range. So-called amplitude correctors are used to compensate this property. This function enables the correct display of the spectral distribution and intensity without the detector's properties influencing the result. The known spectrum of a calibration lamp is recorded to determine the correction curve. The quotient between the measured value of the device and the actual course results in the amplitude correction. The correction function is applied on each measuring operation but can be deactivated manually.
Dark Current Compensation Depending on the detector temperature, a dark current with varying intensity is detected on the detector. This function deducts the dark current from the signal, which leads to less noisy and temperature-compensated results. As this is an automatic function, manual dark current detection and a shutter are not required. Besides the temperature, the dark current also shows a dependency on the exposure time. The function also considers and corrects this effect.
The hard and software described in the following is supplied with each TRISTAN® spectrometer. This way, the user does not have to compile the necessary options, which is tedious and time-consuming and might also result in additional costs. With the purchase of a TRISTAN® spectrometer, the customer receives a fully functioning device and not just an optic cell with interface as provided by other manufacturers.
The electronics of most spectrometers is limited to the necessary modules for reading and controlling the detector as well as for data transmission via a USB port. These spectrometers require an external PC for operation. This provides the entire power supply via the interface and processes the detector's raw data to analysable measuring results. However, the operation of a highly precise measuring device with analog components and Back Thinned Detector requires an interruption-free power supply. This stability is not given with the power supply via the USB port of a PC. This is why each TRISTAN® 5 and TRISTAN® light is delivered with a stabilised switching power supply.
The TRISTAN® 5 and TRISTAN® 5 has a serial interface pursuant to RS232 standard and a USB 1.1/2.0 port. Via these interfaces, the measuring results can be accessed directly with any software. Optionally, the USB port can also be replaced with an Ethernet interface and the TRISTAN® Remote-controlled via LAN without requiring a PC directly at the measuring station
Trigger Input / Output Via the trigger input and output, which is a standard feature of the TRISTAN® 5 and TRISTAN® USB, the time of measuring with the TRISTAN® can be easily synchronised with any processes.
Software TRIWin 3.2 and TRIWin 3.2 Pro TRISTAN® USB comes with the TRIWin 3.2 software package. TRIWin 3.2 uses an intuitive Graphical User Interface which offers many tools for working with collected data, from archiving and documenting to performing mathematical functions for data analysis and curve smoothing. Output can be exported directly to Excel, which makes documentation easy and uncomplicated. Separate laboratory software is unnecessary.
All TRISTAN® 5 and TRISTAN® light spectrometers come with the TRIWin 3.2 PRO software package. The TRIWin 3.2 PRO Upgrade is designed to enhance the capabilities of the TRIWin 3.2 package and to put specialized tools at your disposal. TRIWin 3.2 PRO is equipped for use in laboratory settings where advanced measurements and analysis are routinely performed.
TRIWin 3.2 PPRO features the ability to connect multiple spectrometers for a number of specialized measurement options. Multiple spectrometers can be connected as a group to execute simultaneous measurements. Separate spectrometers can be used within the same operating environment without the need to disconnect any cables or restart the software. TRIWin 3.2 PRO multispectrometer mode is designed to give the utmost functionality to the spectroscopyintensive working environment.
TRIWin 3.2 PRO includes further capabilties for exporting your captured spectra in different graphical formats increasing your options when it is time to present your results. You can choose from: .ems, .jpg, .png, .gif, .tif, and .pdf, each with its specific strengths and functions.
MyInstrument is the basic element for controlling the TRISTAN® spectrometer family on the PC. It enables easy setting of all measuring parameters and starting the measuring operations. The drivers can be easily integrated into other applications. In general, all components supporting ActiveX components can use these drivers immediately. Among them are Microsoft Excel, GRAMS, LabView, Delphi, Visual Basic, etc. |
