Operation of the Spectrophotometer and CFH Filter Scan Naming Convention

Date: February 25, 1997

At long last, here is an operating procedure for running the Shimadzu spectrophotometer. I will describe only the procedure for scanning transmission curves. Reflectance is similar but requires a different attachment.

1) Decide if the sample you have will fit into the small compartment or if it needs to be in the large compartment. The scan region for the small compartment is from 190 - 3200 nm while the large compartment can only scan from 300-2500 nm.

2) Turn the spectrophotometer power on with the on/off switch on the main unit of the spectrophotometer. It is just to the right of the large compartment.

3) Run the UVPC software.

4) From the configuration menu, select Load Parameters. For the widest scan range, select the "fulrange" parameter file for the small compartment or the "lgtrans" parameter file for the large compartment. There are several other parameter files available if these are not sufficient. Two useful ones are smaller range ones ("blurange" and "redrange") for fine scanning of narrow-band filters. You will have to push the exit button to make this dialog box disappear. All of these parameters may be set by hand in the Parameters... box in the Configuration menu. If you are uncertain of the function of a certain parameter, they are explained in the UVPC users' manual which should be near the spectrophotometer.

5) From the Configuration menu select PC Configuration. Set the printers to LPT2: to use the LaserJet printer in the plotter room. Set the Communications port to 2.

6) From the Configuration menu select Utilities... and from the window that appears, select the On box. The spectrophotometer will go through a set of self-test procedures and should pass all of them. This will take ~10 minutes to complete. When complete choose the "OK" button to get rid of the window and finish the setup of the spectrophotometer.

7) With nothing in any of the beams of the spectrophotometer and all of the lids closed, push the Baseline button at the bottom of the screen. This will begin the process of taking a baseline for the machine. It is important to take a new baseline every time the machine is turned on OR when the operating parameters are changed (wavelength range, %T vs %R, slit width, etc.) This will take ~15-30 minutes depending on the parameters.

8) Now the sample (filter) needs to be inserted into the spectrophotometer sample beam. The spectrophotometer uses two beams, a reference beam and a sample beam. It is important to get the filter into the correct beam.

9) With all lids closed once again, push the Start button at the bottom of the screen to begin a scan of the sample. This will take a while, but not as long as the baseline. The scan will appear on the screen as it is being taken.

10) When the scan is finished, a dialog box will appear that asks for a filename and comments. This is a pre-Win95 program, so the name must be 8 characters or less with no extension. The program will add a .spc extension automatically.

NOTE: If you are scanning a CFH filter, use the following naming conventions: cfh+"filter #" where the filter # is the 4 digit code used for CFH filters when the scan covers the full range of the spectrophotometer. If the filter is narrow band (<~20 nm), the filter should be scanned twice; once with the full range and named as above, and once with a reduced range and narrow slit to allow better resolution. The reduced range scan should be named cfh+"filter #"+a. The reason for requiring this naming convention is that I have written a couple of programs that convert the .spc files into text files and write the text files to the filter curve database area. Another program looks at the files and determines the central wavelength and bandwidth of the curves. Both programs need the transmission curves to be named as above to work properly.

The comment can be any comment you like, but normally tells the date and the operator. Pushing Save on this dialog box does NOT save the file to disk. This is only done when you select Save from the File menu. This is important since the data may be lost if not saved from the File menu. All files are saved, by default in the /uvpc/data subdirectory.

This is all that is required to take a scan of a filter. There are a couple of other functions that are useful to know about. The first is translating the .spc file into an ASCII file. This is done using the Data Translation... option from the File menu and following the instructions. The file to be translated needs to be loaded before using this option. The output file will have the same name, but with a .asc extension. All files are saved, by default, in the /uvpc/data subdirectory.

The other is Plot under the Presentation menu. This one allows you to graph the curves for printing. The window that pops up when the Plot option is chosen has a pull-down menu on the right-hand side that will normally be set to Graph. An additional setup window can be found by clicking on the pull-down menu and re-selecting Graph. The window that appears allows you to set which of the currently loaded scans to plot and how you want them plotted. When this window is accepted, you may see a preview of what will be printed using the Print Preview button on the first screen. If it is what you want, the plot will be sent to the printer specified in Step 5. The plots are of mediocre quality, so if you want something that looks good, the best thing to do is to translate the file to ASCII and import it into a program like Excel and plot it from there.

The spectrophotometer is also able to do absolute reflectance measurements, but there is a dip in the measurement at about 800 nm that does not seem to be real. I have not had time to investigate this yet. The absolute reflectance measurement needs a special unit installed an is set for reflectance at 5.