file: ozone_desc.html
29 Apr 2003

OZONECPU Operational Description for Firmware Version 2.26

Refer to the commands document for complete info.


On startup, the logger:

  1. initializes itself and powers up the WNDRAIN module and valve controllers
  2. shuts the valves if they were left open when the system was last worked on or assembled
  3. checks a series of setup parameters in EEPROM (these are the parameters set using the UOK Update command, then proceeds according to the MetMode found in EEPROM
  4. sends a message to the RS232 console then enters the main program loop, running (GO mode) by default), logging MET and status data to FLASH card, and ready to accept commands
  5. assuming MetMode 2 (local MET instrument) is selected, the logger immediately begins checking the MET data
  6. if the wind speed is within limits and it's not raining, a minute later the inlet and outlet valves will open and the PSI OZONE unit will be powered up
  7. every minute the MET data is checked, and:
  8. once shutdown, the STAT command will show a "waiting for rain" or "waiting for wind" message for the duration of the shutdown.
  9. MW can be used to disable wind speed checking entirely; then only rain detection will stop/start the sampling.

During operation, the system status is displayed by:

Only a subset of the logger command set is available when the logger is in GO mode (Running); an H command shows the available commands. When the logger is in STOP mode, a much larger set of commands is available; in particular, all the setup and FLASH card handling commands are only available when the logger is stopped. NOTE: STOP and GO apply to the logger system, not the PSI sampling; the system may be running in GO mode, but OZONE sampling may be stopped if the MET situation is not appropriate for sampling. Again, when STOPPED, an H command will show the full command set available.

Additional parameters in EEPROM are used to set some limits on PSI operation and to setup for periodic ZERO checking by "switching" an ozone scrubber in line with the airflow. These parameters are set under the UOK Update command, as operating parameters OP0 thru OP9 - refer to the OP settings. OP1 and OP2 set the amount of time that the PSI will remain OFF after an error even if the MET data indicates it's OK to sample. OP0 sets the maximum allowable PSI CPU temperature (as indicated in the COM2 data output). OP3 and OP4 set the lower and upper limits of the valve position (normal value is 42, also indicated in the COM2 data output).

Parameter OP5 sets the number of hours between ZERO checks; setting it to 0 disables ZERO checking. This time interval is based on actual sample time, not calendar time. That is, if OP5 is set for 24, then 24 hours of PSI sampling time must elapse between ZERO checks. OP6 sets the duration of the ZERO check in minutes, for example 15 minutes. ZERO checking only happens when it's OK to sample per the MET checking; i.e. the PSI must currently be running for the ZERO check to commence. Once the ZERO check starts, the main inlet will remain closed and the scrubber switched in for the OP6 duration, UNLESS the MET check requires a shutdown due to rain or wind. In this case, the ZERO check may abort part way through. It will NOT be restarted when it is OK to sample again. Normal sampling will simply resume and another OP5 hours interval will commence. Finally, OP9 is ALWAYS set to 60 for normal operation of the ZERO checking. OP9 is the minutes multiplier for OP5, since the timing is internally handled in minutes. (This is useful as outlined below...)

Note that during all operation, the STAT command will indicate, among other things, GO/STOPPED status of the logger, OZONE sampling if the PSI is running, the time left (in minutes) until the next ZERO check, or, if ZERO checking is currently happening, the time left in the ZERO check.

IMPORTANT NOTE about changing setup parameters via the UOK command:


In order to facilitate testing of the system including ZERO checking, OP9 may be set to something other than 60 minutes. Simplest is to set it to 1 so that the OP5 setting now equals minutes for testing. Thus, if OP5 = 24 and OP6 = 15 and OP9 = 1, after every 24 minutes of sampling, the ZERO check solenoid will energize, the inlet will close and for the next 15 minutes, incoming air will be scrubbed. After 15 minutes, the inlet will open, the ZERO check solenoid valve will de-energize, and a new 24 minute sampling period will begin.


If the logger starts up with OP9 set to something other than 60, the STAT command will display a WARNING! message about this, AND the logger will start a 24 calendar hour timeout on ZERO checking that WILL disable ZERO checking for the duration of the logger operation.



  1. Use the TM command to test the WNDRAIN module while attached to the logger.
  2. DON'T CHANGE the RI value under UOK - leave it at 60!!!
  3. When changing parameters, if you get confused, just ABORT and the EEPROM values will remain unchanged.
  4. Use the SETUP command anytime to see the current operating parameters.