Setting the Clock

The datalogger Clock tab can be used to define a schedule at which an automatic clock check will be performed. The datalogger clock will be set if it varies from the LoggerNet server clock more than the amount of time specified in the Allowed Clock Deviation field.

Because it is important to maintain accurate time stamping of your data, there are a few things to take into consideration when setting up a clock check schedule.

Your datalogger clock should deviate no more than ±1 minute per month. Typically, this drift is less than what will be experienced with a personal computer. Therefore, if your computer clock is not synchronized with an atomic clock or other accurate time keeping device, the datalogger clock may be more accurate than the computer clock.

Another point to consider is how the clock checks may affect the timestamp for your data. Let’s say, for instance, that you have a data collection schedule of one minute with a clock set if the two clocks deviate more than two minutes. Over time, the clocks may drift sufficiently that the datalogger clock is set. If the datalogger clock is 12:02:00, and the LoggerNet computer clock is 12:04:15 the datalogger clock will be set to 12:04:15. Therefore, there will be no data for the timestamps 12:03 and 12:04. Conversely, if the datalogger clock is a few minutes faster than the LoggerNet computer clock, the result would be duplicate timestamps that contained different data.

When a record is stored in a data table, the timestamp is not stored along with the record. Instead, when data is retrieved from the datalogger, the datalogger uses the timestamp of the last record stored and the table interval to calculate the timestamp for any previous records. This calculated timestamp is then stored by the server as part of the data record along with the other data values when data is collected. Because of this timestamping method, if the datalogger clock is changed such that it passes an output interval a discontinuity could occur in the records that could cause the timestamps to be incorrect.

In table-based dataloggers the record number can be used along with the timestamp to assure that records are in order, and no data has been missed.

Changing the computer system clock while the display screens are running will terminate the connection for most of the screens. This can also affect LoggerNet operations or even crash the program.