Leviton A7810, Installation And Operation Manual

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11 SYSTEM 

OPTIONS

If you store data in local time, you will have the following issues.

1.

   Local time is relative. Is Local the time where the EMB HubLite exists, or local to where the data 

is stored? If local to the EMB HubLite, you must shift each EMB HubLite data set depending on its 
location.

2.

   There are about 11 time zones in the US. Some observe DST, others do not. These include Alaska, the 

Aleutians, Arizona, Central, Eastern, Hawaii, Indiana, Michigan, Mountain, Pacific, and Samoa.

3.

   When converting to local time, there will be one hour of overlapping data in the fall when the time is 

adjusted for Daylight Savings time, i.e., log entries run 12:45, 1:00, 1:15, 1:30, 1:45, 1:00, 1:15, 1:30, 
1:45, 2:00am. This will prevent you from sorting your data by time in your database.

4.

   In the spring, you will have a gap in the data from 1:59 to 3:00am. This can cause problems if you are 

calculating demand values based on consumption.

5.

   Converting local time to any other timezone usually involves converting it to UTC first.

Using UTC time solves these problems elegantly. The best practice is to store data in the database in UTC 
format and then convert the information when generating a report for the user.
For example, if you wish to draw a graph of kw over Time, prompt the user for a date range, i.e., Jan 1 
midnight to Jan 2 midnight. Take the user specified end points and convert these times from local time  
to UTC. Next, create an SQL query using the new UTC formatted data as your select statement. i.e.,

SELECT * from TABLE where time > ‘2003-01-01 08:00:00’ and time < ‘2003-01-02 08:00:00’

Note the time is 8 hours ahead of local time. This example is for Pacific which is 8 hours off from UTC. 
This will return a list of data points between the two specified time ranges. Next, plot the data on a graph, 
using the UTC times for start and end points. Finally, when drawing the ‘time’ legend on the grap h, convert 
the values back to Local time before displaying. i.e., 2003-01-01 00:00:00 to 2003-01-02 00:00:00. Any 
division lines on the time axis can be handled the same way. The advantage of using this technique is that 
it will properly draw a graph across DST change boundaries. The graph axis is based on UTC time with no 
DST, and will not show a gap or overlap a the time of the change. The axis labeling will be correct as well, 
matching the UTC times precisely.

Another way to handle the conversion is to query and convert all the returned timestamps to local time 
before drawing the graph. This is useful if you do not have detailed control over the graph legend drawing 
process. This technique will not properly graph across DST changes as the graph is based on local time 
including DST changes.

11.5   System logs

The EMB HubLite can keep several log files that report the general operation of the system, not related to 
the normal data logs. These include the following:

Debug Messages:

 The EMB HubLite can run a “syslog” process to record more detailed information about 

its operations, however this log consumes vast quantities of memory quickly, and is disabled by default. 
Click the “start log” button to enable the feature. Click the “end log” button to disable. Note: when the EMB 
HubLite is rebooted, the debug log will be disabled on startup.

Kernel Boot log:

 Startup messages about the Linux operating system startup. This log shows what 

hardware items were detected and initialized.

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