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Parameter Setup Procedure for the Rsm 1000

Coordinating the Computer, A/D, and Spectrophotometer as Necessary to Identify Wavelengths by Time with a Particular Computer

The RSM 1000 and its control software must be correctly configured to ensure that data can be collected correctly. The purpose of this multistep procedure is to find data collection parameters for a particular combination of your computer and A/D board. These tests are not routine; they are necessary only during initial setup and calibration and after changing computers or other electronic hardware. However, should you suspect that your RSM is not performing correctly, this procedure can help you set up your RSM and adjust the software to ensure correct data collection.

This procedure consists of the following steps:

1. Wheel speed confirmation
2. Hardware parameter check
3. Software parameter check

To successfully complete the parameter setup procedure, all three steps must be performed in the order given.

I. Wheel Speed Confirmation

1. Enter the RSM test program by typing “RSM-test” at the MS-DOS prompt.Screen #1 will appear. (Select the image to view a larger version).

2. Select option "W-Wheel speed monitor." This display shows the error (in microseconds) in the speed of the spinning ScanDisk. The target speed in 62.5 Hz.



When one enters the RSM-TEST program (and the RSM 1000 program), the error will be large as the ScanDisk accelerates. After a few minutes, the motor will stabilize with an error of only ± 1 ms, which is one part in 16,000 (screen #2). If the ScanDisk has a larger error, please contact Olis.

II. Hardware parameter check

1. From the System Setup (screen #1) of the RSM-TEST program, select option "A-FIFO throughput test." This test will determine the specific data transfer parameters (from the FIFO buffer on the A/D board to the computer’s memory) for your computer. The test will take 2-3 minutes. It is not necessary to run this test at 1000 kHz. If the FIFO throughput test fails before completion, contact Olis.

2. Exit the RSM-TEST program by pressing "Z;" the new parameters will be retained in the file "RSM-HDW.CFG"—RSM Hardware Configuration.

III. Software parameter check

For the following tests, the lamp must be operating and the RSM must be configured for dual-beam absorbance.

1. Type "RSM" at the MS-DOS prompt to enter the RSM-1000 program. After the automatic monochromator calibration, you will be returned to Command Mode (screen #3).



2. Select option “S-Parameter Setup.” The Parameter Setup Menu will be presented (screen #4). Verify:

   1. the lines of the grating and the blaze wavelength settings in the monochromator parameters block are correct for the gratings you are using in the RSM;
   2. the external trigger is disabled;
   3. the stopped-flow is disabled;
   4. the ScanDisk type is set to "slit;"
   5. the mode is set to "no avg (1000 scans/sec)"
   6. dual-beam mode is selected;
   7. collect scans is set.

   

3. Return to Command Mode by pressing "Esc."

4. Enter Live Display by pressing "V." In Live Display:

   1. select 450 nm as the center wavelength (option “M”); make sure that the RSM shutter is open, if appropriate;
   2. adjust the high voltage on the PMTs (option “A”);
   3. insert the holmium oxide filter in the light beam path; Live Display should look like screen #5;
   4. set the collection time (option “T”) to 0.2 sec;
   5. collect data (option “C”).

   Note: Do not collect baseline, since the absolute spectrum is of no particular interest in this case.

    

   

   Examine the data in the 3D display (option “T-Create/display 3D data”). Since the sample is not changing during data collection, all scans should be identical. Press “shift–“ (shift key and minus sign simultaneously) or “–“ (minus sign) to adjust the Z skip for better display, if necessary.

5. The problems one should look for are:

   1. “Error: Check FIFO speed” message appearing immediately after data collection (even though the data look good);

   2. “gaps” or wavelength shifts of some scans relative to the rest (screen #6.3);

   3. noise spikes on some scans, especially in the red end of the scans (screens #7.3 and #8.3—the only difference between these data is the amount of noise; as the adjustment approaches the correct values, the noise becomes less evident);

      The same problems can be seen in the 2D slices of the data set (screens #6.2, 7.2, and 8.2; these are 2D displays of the 3D data in screens #6.3–8.3). However, because only nine scans are shown in the 2D display, the effected scans would have to be among the nine displayed in order for one to see a problem. One can use the “D–Extract/display 2D data” option to select scans for display from the entire data set.

      Similarly, the kinetic trace displayed in 2D view must be extracted at a wavelength at which problems exist. One can select kinetic data for display by using the “K–Extract kinetic trace” option in the Cursor Mode screen.

      For these reasons, it is often easier to spot the problems using the 3D display.

      Screens 6.2 and 6.3: Gaps in data (as described in step III.5.b.)
      Screen #6.2
      Screen #6.3

      Screens 7.2 and 7.3: Noise at ends of scans (as described in step III.5.c.)
      Screen #7.2
      Screen #7.3

      Screens 8.2 and 8.3: Noise at ends of scans (as described in step III.5.c.); these noise spikes are more subtle than those shown in screens 7.2 and 7.3)
      Screen #8.2
      Screen #8.3

6. The problems described above can be corrected by fine-tuning a critical data-collection parameter called "FIFO Adjustment." To change this parameter, enter the Parameter Setup menu by choosing option "S–Parameter Setup" from the Command Mode screen. The FIFO adjustment option is not displayed among the Parameter Setup options—it is a hidden command. To access the hidden FIFO adjustment option, press "Ctrl" and "F" simultaneously. A warning message will be displayed. Press "Ctrl" and "F" simultaneously again. Enter a new value for the FIFO adjustment parameter. The value can be set in the ±50 range. Having entered a new value, exit from the Parameter Setup menu by pressing "Esc." Collect data as described previously and examine the data. Repeat the adjustment process as necessary to eliminate the problems described in step #10. Once the proper data collection parameters are found and there are no problems, the FIFO adjustment should not be changed.