Loading HCHO Interface

The algorithms that control all aspects of Harvard FILIF can be accessed via Cygwin installed on the HCHO GSE

1. Open up a Cygwin window

2. Type cd /home/hcho/

3. Type ./doit in order to start the HCHO instrument algorithms. The interface only loads if the electronics box is powered on and you're connected to the same network as the instrument.

Navigating between windows: The keystroke to use when navigating between windows is 'CTRL-A-n' to go forward and 'CTRL-A-p' to go back.

4. To get a graphical interface, start Matlab and type 'rt_hcho'

5. In order to initiate plotting you have to click on CONNECT in the upper left corner

Quick Start: Data Collection

Assuming that all electronics and the laser are powered up and the pump is running, the following commands should be issued to start data collection. This command sequence also assumes that the scan range is already defined (such as scan start, scan stop, and step size) as well as the offline position relative to online (offline delta), the dither step, and the number of points collected at the online and offline position.

> swStat Pressure Control Activate starts a PID algorithm that adjusts the setpoint on the bypass MFC in order to get a pressure reading of 115 Torr inside the detection cell. If the bypass MFC setpoint goes to zero or full scale without reaching a pressure of 115 Torr, then the needle valve adjacent to the inlet of FILIF should be opened or closed accordingly.

> swStat Chop Dither Enable ensures that the dithering functionality is enabled. Dithering is helpful to stay on the online position between full scans and helps to minimize the number of times a full scan needs to take place during data collection.

> swStat chop start 30 Minute Scan Interval (also available in intervals of 1, 5, and 10 minutes; values can also be adjusted in algo). This command formally starts data collection by first performing a full spectral scan and using the reference cell signal to identify the online position. After a full spectral scan is performed, the algo automatically starts tuning the laser between the online and offline positions based on the settings defined under Laser Control. After 30 minutes (or whatever interval is used) another full spectral scan will be performed before going back to the online and offline positions.

A note about data collection: The algorithm runs on the onboard computer on the HCHO instrument. Raw data is also saved onboard the HCHO instrument. This is immensely helpful since it means the Lenovo laptop can be disconnected from the network (or turned off) and the HCHO instrument will still be collecting data with the settings that you last applied. True story from a study at MIT: Since the Lenovo laptop randomly turns off or updates itself, this feature has meant we were still collecting data in the background!

Stopping Data Collection and Saving Data

To stop data collection and process the data, please issue the following commands:

> swStat chop stop should be issued first and should not be issued while a full spectral scan is being run (rather wait for the algorithm to do one complete cycle of online and offline sampling before issuing the command as the workup script doesn't like it when the file ends on a scan).

If necessary, remember to turn off any flows from the calibration box, and turn Valve 1 off. You don't want to accidentally waste your calibrated HCHO gas cylinder standard if it's connected!

> quit will quit out of the interface, stop data from being saved, and return you back to the terminal screen.

If you want to return to the terminal screen WITHOUT stopping data collection, then you should type > exit in the command window.

$ reduce should be issued at the command prompt to start the save process between the onboard instrument computer and the laptop.

After typing reduce, you then select which folder you wish to save the data by typing one of the options mentioned. The two most popular options I've used have been data and junk, but you can also be fancy and save data in flight, preflight, and calibration. After pressing enter, the reduce algorithm will then ask you to enter a description of the run. Type in whatever text will help you remember what the file contains! Since you will likely collect many data runs, skipping over this step is ill-advised! After you have typed in a description, press enter and then add a period before pressing enter again. The data is now being copied from the FILIF onboard computer and hard drive to the GSE. This process can take several tens of minutes if you have a large file!