Updating a-Sphere pure water calibrations
Contents
1. 50f52. Processing Template pxt file from Hobi Instrument Services It uses features first added in version 2 00 or 200 of the template file e Open the processing template file in IGOR Pro e From the a Sphere menu select Load Calibration File and navigate to the existing calibration file for your a Sphere e Select Load Pure Water Data and navigate to and select the PWL BIN file e When asked Load separate dark file click Yes and select the PWD BIN file It is acceptable to click No and skip loading of the dark data but that will produce slightly less accurate results Igor will now present a graph like the following This example plot shows a long data set collected over several hours to illustrate the full capabilities of the software but it is OK if your data set is smaller even just a few samples Page 30f 5 Calculate NR 41 8 5 00 PM 5 30 PM 6 00 PM 6 30 PM 5 2 15 dat 0 1000 2000 l l O graphwaveD pnt 567 150502 1734 42 512 Ax 2649 C B graphwavel pnt 622 150502 1813 Y 42 593 AY 0 080837 It is also OK if your data includes multiple distinct sets of data separated by hours or days In that case you can zoom in on portions of the data using IGOR Pro s standard controls The slider control at the bottom of the graph selects one wavelength to display By Sliding it back and forth you can observe how different wavelengths varied with time Note that some wavelengths are ou
3. Updating a Sphere Pure Water Calibrations www hobiservices com David Dana 2015 8 11 Introduction The a Sphere in situ spectrophotometer is calibrated to measure the spectral absorption coefficient of any fluid flowing through its spherical sample chamber Several factors cause the calibration to change with time primarily aging of the light emitting diodes in the light source Long term changes in the LEDs can be compensated for by measuring the a Sphere s response to pure water This is part of the normal calibration process at Hobi Instrument Services but can also be done by properly equipped users The pure water calibration process is also helpful for testing how well the integrating cavity has been cleaned and for observing long term changes in the cavity Prerequisites This document assumes familiarity with e general operation of the a Sphere e a Sphere processing software based on IGOR Pro and e using RadSoft for real time communication with the a Sphere For more about these see the a Sphere User s Manual and the separate document Using RadSoft with the a Sphere The procedures require these programs and files e IGOR Pro version 6 2 or later e a Sphere Processing Template pxt version 2 00 or later e RadSoft e PWL CMD and e PWD CMD Processing requires the IGOR Pro project a Sphere Processing Template pxt version 2 00 or later The procedures require a source of highly purified wa
4. er the temperature of the water e Anew plot will open showing the average spectrum of the data you selected 140 120 100 80 60 40 20 Collecting a new air reference spectrum An air reference spectrum collected with the sphere completely empty and dry is sometimes useful for checking the cleanliness and stability of the a Sphere Pure water measurements are the best method for doing this but air spectra can be collected more easily and without special equipment You can collect and update an air reference using very similar procedures to those for pure water with the following differences e After cleaning the sphere ensure it is completely dry inside If necessary leave it open to allow water trapped around the windows and edges of the sphere to evaporate Depending on the environment this could take up to several hours e On the a Sphere use the AIRL and AIRD commands instead of the PWL and PWD commands e In RadSoft use level 5 data display which will normalize the data to the previous air reference instead of the previous pure water spectrum Saving a new calibration file To store a new version of the calibration file select the Save Igor Calibration File command from the a Sphere menu in IGOR Pro The file will contain the last pure water and air reference spectra if any you processed You can also save a version of the file for use with RadSoft using the Save RadSoft Calibration File command Page
5. lar instrument e Type PWL This will collect and average 50 samples then send the averaged spectrum to RadSoft e To observe whether the values are stable type START PWL This will continuously collect new 50 sample averages and display them Type STOP to stop the data collection after it completes the current average or press ctrl C repeatedly to stop it immediately e Preferably after collecting satisfactory data drain open and clean the sphere again and repeat the data collection If the sphere is perfectly cleaned the values should not change significantly after additional cleaning After a period of extensive use it is not unusual for the sphere to require several cleanings e When finished turn off power to the a Sphere Data you collect during this process will be stored on the a Sphere in files called PWL BIN light data and PWD BIN dark data The PWL and PWD commands append new data to any existing PWL BIN and PWD BIN files on the a Sphere so data you collect with this procedure will accumulate in those files until you delete them It is OK and sometimes helpful to let these files grow large in order to maintain a record of multiple pure water calibrations The date and time are stored with each data sample After collecting data use the RadSoft device explorer to copy the PWL BIN and PWD BIN files from the a Sphere to your computer Processing pure water data This process requires IGOR Pro software and the a Sphere
6. t of the useful measurement range and will display zero or other meaningless values But all the wavelengths in the range of approximately 360 to 750 nm should contain valid data The purpose of this display is to allow you to see trends in the data over time in order to evaluate the quality of your pure water measurements At Hobi Services we typically record a number of measurements interspersed with cleanings of the sphere in a single file Then we can see the effect of successive cleanings When the raw Signals reach a stable maximum the sphere is as clean as possible Wavelengths longer than about 650 nm are affected by water temperature so they may have a different trend from shorter wavelengths The example plot above shows data at 734 nm where the temperature effect is quite strong The rising trend in this case is probably due to decreasing water temperature Because of this effect it is best to judge the quality of data only at wavelengths below 650 nm It is also important to measure and note the temperature of the water at the time of calibration since in situ measurements will show temperature effects at the longer wavelengths Once you have determined what range of data best represents pure water e Drag the round cursor from the toolbar below the graph window onto the first data point you wish to include e Drag the square cursor onto the last point Page 4of5 e Click the Calculate button e You will be prompted to ent
7. t useful to select level 4 processing which displays the data normalized by the pure water spectrum contained in the current calibration file This makes it easy to see how the spectrum has changed and sometimes to see when cleaning is needed For example a spectrum that falls off rapidly at short wavelengths likely indicates the sphere is contaminated with UV absorbing organic matter A spectrum with narrow peaks or troughs likely indicates changes in individual LEDs centered at those wavelengths For more details about processing and display options see the separate Using RadSoft with the a Sphere Procedure Note commands typed into the RadSoft terminal window are shown in upper case for clarity but are not case sensitive Commands are sent when you press the Enter or Return key e Connect to the a Sphere with RadSoft and open a terminal window to allow typing commands to the a Sphere and seeing the a Sphere s responses e Using the RadSoft Device Explorer copy the files PWL CMD and PWD CMD to the a Sphere e Fill the sphere with pure water If possible allow the water to flow continuously during the test e Type WARMUP in the terminal window If the a Sphere replies with READY proceed If not type START WARMUP and wait until it indicates it is ready Page 2of5 e Type AUTO This will set the integration time appropriately It should show a value between 95 and 250 ms depending on the characteristics of your particu
8. ter such as a Millipore Milli Q or equivalent system Collecting pure water data Setup Prepare tubing and fittings to allow flowing pure water through the a Sphere while it is Standing vertically sohere end down The vertical orientation provides the best flushing of air from the sphere when filling it This requires a right angle fitting on the Page 1 of 5 bottom inlet to the sphere The outlet on the side of the a Sphere can be either right angle or straight Ideally flow water directly and continuously from your purification system into the sphere But if that is not practical you may flow water that has been stored in a suitable carboy Cleaning Thorough cleaning is essential for accurate results In most cases merely flowing pure water through the sphere is not sufficient to clean it We have found that Alconox detergent diluted according to the manufacturer s instructions is the most effective cleaner Apply the liquid cleaner liberally to a soft cloth or paper towel and wipe it directly on the surface of the sphere then rinse it with pure water It may be necessary to repeat this process several times to achieve optimum cleaning You can use RadSoft to observe the data after each cleaning Cleaning tends to have the largest effect on UV wavelengths where dissolved matter has highest absorption Data Display RadSoft will automatically display data you collect in a graph that has many options Typically it is mos
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