Data Sheet Optical Transmission Meter
Contents
1. INNOVATIVE TREATMENT SOLUTIONS Transmission Meter for methylene blue test solution Description PA ia eid 3 ered ie Maididys ms bag I Background The German standard DIN 52980 Photo catalytic activity of surfaces Determination of the photo catalytic activity by degradation of methylene blue asks for a measurement of the optical absorbance in order to quantitatively determine the degradation rate Due to an absorption band of methylene blue in the range of 664 nm the measurement shall be performed at a wavelength of 664 5 nm The transmission meter of MRC is designed to conduct this measurement Transmission meter user manual version 2 25 04 2013 page 1 of 8 INNOVATIVE TREATMENT SOLUTIONS 2 Brief description The transmission meter comprises a red LED a calibrated photo diode a flexible mounting bracket and the required electronics The LED emits light at a wavelength of 659 11 nm 1 e exactly in the absorption band of methylene blue see figure 1 A decrease of the methylene blue concentration thus leads to an increase of the transmission of the LED light through the solution This increase 1s measured by the photo diode Methylene blue test Transmission spectrum through 7mm methylene blue 7 29mg I 100 Transmission LED 660nm 80 60 Figure 1 Emission spectrum of the LED red and transmission curve of methylene blue solution blue The peak of the LED lies in the absorption2. We have implemented a couple of features in order to enable stable measurements e Current stabilization of the LED compensation of power variations due to temperature drift e Electronic chopper for offset suppression against room and ambient light e Electronic noise suppression e Coloured glass filter Schott OG530 for suppression of ambient light Transmission meter user manual version 2 25 04 2013 page 3 of 8 INNOVATIVE TREATMENT SOLUTIONS 4 1 Adjustment of the optimal signal range The LED intensity and the amplification of the photo diode should be adjusted in that way that the signal range for unbleached and maximally bleached solution is fully utilized For this purpose a preparation measurement with distilled water in the sample container should be performed under the expected ambient conditions Hereby the adjustment can be carried out in the following way e LED intensity The electronics can be adjusted to the maximum expected light intensities with distilled water in the sample container You should increase the intensity with the potentiometer until the LED indicator marked with Saturation is not just yet shining This process does not depend on the chosen amplification e Amplification of photo diode In order to adjust the amplification you should connect the output signal to a multimeter Still you should have distilled water in the sample container By turning the potentiometer for the amplification you
3. band of methylene blue around 664 nm 40 Transmission Intensity a u 20 600 640 660 Wavelength nm 3 Mounting bracket LED and photo diode are integrated into a special mounting bracket which enables a flexible positioning at different sample containers Figure 2 Mounting bracket in horizontal left and vertical right orientation 3 1 Option with flow cell As an option we offer a modified version of the mounting bracket which can be connected to a flow cell The optoelectronic components are the same but it is mechanically optimized for the small dimensions of the flow cell Transmission meter user manual version 2 25 04 2013 page 2 of 8 INNOVATIVE TREATMENT SOLUTIONS Figure 3 Combination of mounting bracket with flow cell 4 Electronics Figure 4 shows the front side of the electronic box with different elements At the bottom there are connectors for the cables of the LED and the photo diode as well as for the transmission signal output The signal can be read out by any multimeter Alternatively 1t can be recorded on a data logger Two potentiometers at the top can be used to adjust the LED intensity and the amplification of the photo diode respectively The function of the saturation indicator is described in section 4 1 The on off switch and the connection for the power cable are on the rear side of the electronic box Figure 4 Electronics of the transmission meter
4. e care for a stable connection Please avoid any dye in the flow cell support since it would distort the measurement It is hard to clean the support Thus if any dye gets into the support please contact the manufacturer In order to fix the tubes to the flow cell we include appropriate hose clips in the delivery 5 2 Peristaltic pump A peristaltic pump is used to recirculate the test solution see figure 7 The flow rate is adjusted to a value which according to our experience enables a sufficient mixing of test solution in the sample container Transmission meter user manual version 2 25 04 2013 page 5 of 8 INNOVATIVE TREATMENT SOLUTIONS Pumpe Messsysterr Figure 7 Peristaltic pump at housing The flow cell with the connected tubes is mounted a the right side The peristaltic pump is integrated in a UV stable aluminium housing so that it can be used directly in the illumination chamber There are screws at the housing to mount the flow cell The pump is powered by a wall power supply Notes 1 Especially when you replace the tubes it can happen that air is getting into them Please make sure that air is not accumulating at the transmission window of the flow cell where it would distort the measurement The elimination of air is easier if you turn the flow cell in an upright position as shown in figure 3 If an air bubble is fixed to the transmission window i e in a stream burble you can try to res
5. olve and remove it by snapping with your finger and actively moving the tubes 2 Please take care to keep the transmission window in a clean state 3 If the flow cell is wetted with methylene blue or other dyes you should recirculate it with distilled water in order to avoid a dry coating 5 3 Sample container Figure 8 shows the example of a sample container which can be integrated into a closed loop For an easy performance of a continuous measurement we have equipped the container diameter 80 mm height 45 mm with a top frame which carries tube connectors and a UV transmitting glass cover The container accepts samples with an area of 50x50 mm Note The absorption of the chosen UV glass cover at a wavelength of 365 nm is about 11 The test solution in the container can be circulated through a flow cell by means of a peristaltic pump to which the bracket for the transmission measurement can be connected We have selected tubes which do not absorb methylene blue and which are stable against UV illumination Transmission meter user manual version 2 25 04 2013 page 6 of 8 INNOVATIVE TREATMENT SOLUTIONS Figure 8 Sample container with tube connectors and glass cover 6 Technical data subject to change Light source Kingbright L 1513SRC C Spectrum is shown figure 1 Photo diode Centronic OSD15_ 5T Wavelength range 400 1 050 nm Sensitive area 15 mm Sensitivity 0 21 A W Dark current 3nA Meth
6. s An insufficient mixing of the test solution can affect the measurement results e g 1f solution close to the sample s surface is already bleached but the overall solution shows a different average concentration and therefore another absorbance If the transmission is measured at a wrong position you will get incorrect values then The German standard therefore suggests that the solution is stirred in periodic time intervals As an option we offer a set of components which make it easier to determine the concentration according to the standard The stirring of the test solution was carried out by recirculating it in a closed loop Figure 6 schematically shows the respective setup Peristaltic pump Flow cell Figure 6 Setup with sample container flow cell and peristaltic pump for continuous measurements of the methylene blue concentration 5 1 Flow cell The central element of this setup is a flow cell with a defined optical depth Since the liquid column which is relevant for the transmission measurement has a constant thickness this setup has the advantage that it enables absolute concentration measurements after a one time calibration of the mounting bracket If the adjustment of the LED intensity and the photo diode is carried out once there is no need for additional modifications In the electronics described in section 4 2 this adjustment is already made Notes e Ifyou connect the tubes to the flow cell please tak
7. s or air bubbles in the flow cell dirt or debris and further aspects have an effect on the calibration That is why the calibration should be checked from time to time e The measurement of voltages at a couple of known methylene blue concentrations and comparison with the original calibration can give a good indication for the reliability of a calibration Each calibration will lead to a new fitting curve and formula Transmission meter user manual version 2 25 04 2013 page 8 of 8
8. should reach a voltage of less than 5V 5V is exactly the saturation voltage of the amplifier We recommend a value of about 4 5 V If you have a vertical orientation of the mounting bracket we recommend to place the photo diode in the upper position since it will catch less interfering background light in this position In case of a bright environment you can reduce the saturation limit But this will limit the dynamic range signal to noise of the photo diode 4 2 Option with fixed adjustment for the flow cell As an option we offer an electronic control where the LED intensity and the amplification of the photo diode are already adjusted to fixed values This option is usually chosen in combination with a flow cell It has the big advantage that after a single calibration you have a defined correlation between the signal output voltage and the methylene blue concentration The internal adjustments of the LED intensity and the amplification of the photo diode are optimized for transmission values which occur with typical methylene blue concentrations according to the German standard DIN 52980 Figure 5 shows a photo of the respective electronic box Transmissions messung Signal OUT Figure 5 Electronic box of the transmission meter with fixed adjustments Photodiode LED Transmission meter user manual version 2 25 04 2013 page 4 of 8 INNOVATIVE TREATMENT SOLUTIONS 5 System for continuous measurement
9. ylene blue test Linearity of signal for absorption measurement RESPONSIVITT A SW Measurement Detector output voltage V 0 20 40 60 80 100 120 140 200 300 400 500 600 700 8OO 800 1000 1100 1200 Reference mV WAVELENGTH nm Figure 9 Left Output signal of the photo diode vs intensity of a reference signal Right Spectral sensitivity of the photo diode Transmission meter user manual version 2 25 04 2013 page 7 of 8 INNOVATIVE TREATMENT SOLUTIONS 6 1 Accessories Flow cell Hellma Analytics 10 mm 178 010 OS Z 8 Peristaltic pump Gemke LP 60 Rotational speed 30 TPM Flow rate 14ml min Tube at pump Silicone else PVC Thickness 2 8x4 2 7 Appendix Calibration of voltages vs methylene blue concentration The following figure shows voltages for different methylene blue concentrations recorded with the transmission meter and a flow cell Transmission vs methylene blue concentration Measurement Exp fit Voltage U V BP 29 06 11 Concentration C umol l U 3 6 exp C 7 69 0 6 Figure 10 Typical calibration curve Voltages vs methylene blue concentration At the low right of the diagram the formula for the voltages and the dye concentration is displayed as a result from fitting The formula can be used to calculate the concentrations from measured voltages Notes The calibration strongly affects the resulting photo catalytic activity Coating of dye
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