Filter wheels

FW = filter wheel FB = fiber optic bundle LS = light source PP = peristaltic pump. Tlie colorimetric reading stations are marked 1 through 9. 

Photometric Moisture Analysis TTis analyzer reqiiires a light source, a filter wheel rotated by a synchronous motor, a sample cell, a detector to measure the light transmitted, and associated electronics. Water has two absorption bands in the near infrared region at 1400 and 1900 nm. This analyzer can measure moisture in liquid or gaseous samples at levels from 5 ppm up to 100 percent, depending on other chemical species in the sample. Response time is less than 1 s, and samples can be run up to 300°C and 400 psig. 

The interferometric measurements with RIfS can be parallelized as demonstrated in Figure 18. In this case, instead of white light interferometry, only a few wavelengths are used to allow parallel detection of all measurement dots. A filter wheel selects one wavelength at a time from the white light source, while the CCD camera monitors the intensity distribution at the transducer for all spots, in this case in a microtiter plate35. 

To obtain color images with a HCCD camera, filter wheels will be used, in which each filter will be chosen specifically for one fluorescent label, in emission and in excitation. For CL or BL work, one filter wheel is sufficient. For fluorescence, two are necessary (see, for instance, in Fig. 3 the positioning of the filter wheels in the optical path). If, for instance, a three-color experiment is performed, an image will be acquired for each label with the adapted filter(s). The three gray-level images are sequentially acquired. They will then be colored ... 

Fig. 1. Typical locations for CAM components, showing the photometer, 1 filter wheel, 2 monochromator, 3 shutter and aperture unit, 4 beam splitter, 5 accessories for polarized light such as a rotary analyzer and a compensator, 6 beam splitter for epi-excitation fluorescence, 7 objective lens, 8 stage, 9 substage condenser, 10 condenser aperture, 11 polarizer, 12 field aperture for photometry, 13 shutter, 14 primary illuminator, 15 arc lamp, 16 shutter, 17 monochromator, 18 filter wheel, 19 and ocular, 20.

C = Filter wheel with a series of colour filters,... 

Figure 6.6 Example components available for simple photometers (A) a dual channel detector, (B) a quad, four-channel detector, (C) an example filter wheel with 8-filter channels, and (D) example MEMS-based IR...

The system uses independent filter wheels (Fig. 2) with up to 16 different filters for excitation (270-550 nm) and emission (310-590 nm) and performs measurements in steps of 20 nm, which was found to be most suitable without any loss of information. The number of measurements for each filter position can be individually chosen. Adapted to the different industrial processes, properties and steps of filters can be designed individually to cover most of the information potential. In addition it is possible to monitor single-wavelength pairs continuously. A high measuring frequency (10/s) enables in situ mixing time experiments for bioreactor characterization [49]. The singlewavelength pairs could be selected dependent of the available or suitable fluorophores. 

Figure 6. A diagram of the chopper/filter wheel used in the fast response, ln-sltu CO2 sensor. Combining both functions on a single wheel provides the precise timing necessary to minimize electrical filter interference and significantly reduces instrument weight and volume. Coating sample and reference...

The instrument works in a semi-continuous way. First, the pump purges the sample lines and the measurement cell in order to flush out the old sample and bring in the new one. The valves to and from the measurement cell are then closed and measurement starts the IR source is turned on, the chopper wheel starts rotating and the microphones pick up the photo-acoustic signal. The optical filter wheel positions each of the optical filters in the light path, one after the other, until all filters have been measured. Finally the instrument calculates the concentration of each gas, the results are displayed and the whole procedure starts all over again. 

One optical filter for the measurement of water vapor is installed in the filter wheel as the standard. In this way, the water vapor is measured in each sample, enabling the instrument to subtract the absorption signal coming from water vapor from the measured signal for a gas of interest, giving a more correct measurement. Similarly, by measuring the same air sample with more optical filters, one filter selected for each gas in the sample, it is possible to compensate for the interference of one gas on another. 

Another strategy is to utilize single multiband dichroic mirrors and emission filters and separate exciter filters either in an external slider or filter wheel. This will preserve the image registration and reduce mechanical vibrations, but the trade offs are a reduced brightness of the fluorescence, limitations on how many different probes can be separated, and reduced dynamic range and sensitivity due to the necessary color CCD camera. 

XF231 DAPI/ FITC/ TRITC Single exciters for each dye can be housed in external filter wheel, triple band dichroics and emitters housed in filter holder... 

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