Campbell-scientific LoggerNet Datalogger Support Software Manual de usuario descargar pdf (Pagina 112)

Section 4. Setting up Datalogger Networks

4.2.6 Setting the Clock

A datalogger’s Clock tab can be used to define a schedule at which an

automatic clock check will be performed. The datalogger’s clock will be set if

it varies from the LoggerNet server’s 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, unless you have a scheduled task on your computer

which synchronizes your computer’s clock with an atomic clock or other

accurate time keeping device, the datalogger’s clock may be more accurate

than the PC’s clock.

Another point to consider is how the clock checks may affect the time stamp

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’s clock is set. If

the datalogger’s clock is 12:02:00, and the LoggerNet computer clock is

12:04:15 the datalogger’s clock will be set to 12:04:15. Therefore, there will

be no data for the time stamps 12:03 and 12:04. Conversely, if the datalogger’s

clock is a few minutes faster than the LoggerNet computer’s clock, the result

would be duplicate time stamps that contained different data.

For the CR10X-TD family of dataloggers, when an instruction

P84 Output Record is executed in the datalogger program to create

an interval based table and a record is stored, the time stamp is not

stored along with the record. Instead, when data is retrieved from

the datalogger, the datalogger uses the time stamp of the last

record stored and the table interval to calculate the time stamp for

any previous records. This calculated time stamp 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 time stamping

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 time stamps to be incorrect. Event-based data

storage does not rely on a calculated time stamp. Data stored to a

table based on an event includes a time stamp in the table.

In table-based dataloggers the record number can be used along

with the time stamp 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.

NOTES

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