Canadian Brewer Spectrometer Network

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====== DSP ======

DSP is a command to perform a dispersion on the Brewer Spectrometer. This command cannot be ran together with other commands as one command string, and must be ran by itself.

===== Dispersion Calibration - Brewer Spectrometer =====

A dispersion calibration is performed to determine the relationship between the micrometer movement (steps) and the UV wavelengths passing through the exit slits of the slit mask. The UV spectrum of three different lamp sources, mercury, zinc and cadmium are scanned (PMT counts vs. wavelength) and the peak width and peak max are determined.  With the use of dispersion specific software the coefficients for ozone and sulphur dioxide are calculated using this spectral data.

The following is a step-by-step SOP detailing the dispersion calibration procedure.

Note: Environment and Climate Change Canada (ECCC) uses DisPro to process dispersion data. DisPro is a software created by International Ozone Services (IOS) Inc. ECCC has access to DisPro via a license from IOS Inc.

==== Pre-Calibration ====

Prior to performing the dispersion calibration, the brewer must first be operationally stable and in good working order.  A series of test are run and are compared to the historical data of this instrument to determine the brewer’s current operational state. 

As a minimum the following pre-calibration tests should be performed and deemed to have passed before the dispersion calibration can proceed.

  * Status and Control (ST) for Iris and filter wheels,
  * Zero zenith prism (ZE)
  * Slit Mask Motor Timing Test (SH) 
  * Print out A/D monitor (AP)
  * Slit Mask Run/Stop test (RS)
  * Photomultiplier Dead Time test  (DT)
  * Grating Synchronization (HP, for MKIII Brewers only)
  * Mercury Wavelength Calibration (HG)
  * Standard lamp test (SL)
  * Confirm gradient offset (GA, for MKIII  Brewers only)
  * High voltage test (HV)

Refer to Kipp & Zonen Instruction Manual for test descriptions and how to interpret results.  Adjustment and changes to optimize the brewer should be performed at this point.

==== Dispersion Calibration Procedure ====

=== Equipment Required ===

  * Mercury vapour lamp and power supply
  * Cadmium vapour lamp and power supply
  * Lamp cradle housing
  * UV protective glasses 
  * Kimwipes

=== Equipment Setup ===

  - Place and center lamp housing over the top of the UV dome.
  - Remove the lamp appropriate storage plug from the lamp housing by loosening the two side screws and lifting the lamp holder (in the case of the mercury lamp, remove the smaller of the two plugs) and carefully slide in the lamp. The Cadmium lamp has a 'Max Output' port, be sure that the port is directed down toward the UV dome.
  - Plug the lamp into its specific power supply, plug the power supply into an outlet and turn on.
  - **__While wearing UV safety glasses__** lift the lamp housing and quickly look to see if the lamp is on.
  - Re-place and center the lamp housing on the UV dome.
  - Go to the computer of the Brewer being tested.
  - If the brewer is mounted on a tracker, turn the trackers azimuth function off via the IC command in the instruments DOSBOX window.

=== Dispersion Initialization ===

  - Begin the dispersion calibration routine from the home brewer control screen.  For the purposes of this SOP Brewer 008 is the instrument being calibrated. \\ {{:pictures:screenshot_from_2023-10-16_15-31-46.png?400|}} \\
  - Press '//Home//' to home out the instrument 
  - Type '//pd//' in the command line and press enter. The pd command writes the data file into the Brewers D file.
  - Type '//dsp//' and press enter.
  - Press the number associated with the lamp being used. \\ {{:pictures:screenshot_from_2023-10-16_15-32-37.png?400|}} \\
  - Press //y// or //n// and then press enter (n is pressed only if the lamp has been on for a minimum of 10 minutes). \\ {{:pictures:screenshot_from_2023-10-16_15-32-59.png?400|}} \\
  - Press '//2//' to select UV Dome and then enter. \\ {{:pictures:screenshot_from_2023-10-16_15-33-45.png?400|}} \\
  - If the program determined wavelengths correspond with the table below, press '//A//', if not press '//R//' to correct. \\ {{:pictures:screenshot_from_2023-10-16_15-34-03.png?400|}} \\ //Note:  The wavelengths used to conduct dispersion calibrations for single brewers (S) and double brewers (D) are tabled below. The DSP calibration script automatically determines the wavelengths that will be used based on the brewer model being tested.//
  - Press //enter// when ready.
  - Typical screen display during a dsp test.  Note: The highest counts should be near the middle of the scan, center portion of the center column.
  - Once the dsp test has completed the brewer will return to menu mode.  Type '//pd//' and then press enter to write the dsp results to the D file. 
  - Using the most recent D file confirm that the Hg’s have “passed” and that there is not a step difference greater than one from the offset to the target number of steps. If this is not the case, do not proceed with the remaining lamps until the cause in discrepancy has been corrected.  The lamp that was tested will again have to be re-run. The D file is located in the instruments data directory. \\ {{:pictures:d_file_image.png?400|}} \\
  -  If the before and after dispersion Hg are within one step, turn off the lamp that was tested, allow it to cool then remove and store it safely.
  - Repeat the above procedures for the remaining lamps.  
  - Once completed, return the equipment to its storage case and close. Also, return the Brewer and tracker to its normal operation.

For more information refer to the {{ :docs:dispersion_calibration_sop_2020_v2.1.pdf |dispersion SOP}}.
====== Lamps ======

===== Mercury (Hg) =====
The lines that are scanned on a Single Spectrophotometer are the following,
^Line^Start Slit^End Slit^Wavelength^
|1|0|2|2893.60|
|2|0|5|2967.28|

The lines that are scanned on a Double Spectrophotometer are the following,
^Line^Start Slit^End Slit^Wavelength^
|1|0|1|2893.60|
|2|0|3|2967.28|
|3|0|5|3341.48|

===== Cadmium (Cd)=====
The lines that are scanned on a Single Spectrophotometer are the following,
^Line^Start Slit^End Slit^Wavelength^
|3|0|5|3080.82|
|4|0|5|3133.17|
|5|1|5|3261.06|

The lines that are scanned on a Double Spectrophotometer are the following,
^Line^Start Slit^End Slit^Wavelength^
|4|0|5|3080.82|
|5|0|5|3133.17|
|6|0|5|3261.06|
|7|0|5|3403.65|
|8|1|5|3499.95|
|9|5|5|3611.51|


====== Notes ======
Typically on instruments with a small slit 0 (and occasionally with instrument with a narrow offset slit 0) you may find the Fit to be closer to around 100pM. This is normal however it is suggested to use a quadratic dispersion as it usually is more accurate than a cubic dispersion.\\
{{:pictures:dsp_fit_results.png?400|}}\\
You can also see a difference in the slit 0 wavelength. This is not considered as a problem and just how the instrument was built. The dispersion will characterize the instrument properly\\
{{::dsp_abs_results.png?400|}}\\

====== Brewer Test Plot Comparsion ======
Place holder.