Campbell CR1000X, Руководство по эксплуатации продукта

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NOTE:
There is no such thing as NAN for integers. Values that are converted from float to integer
will be expressed in data tables as the most negative number for a given data type. For
example, the most negative number of data type FP2 is –7999; so, NAN for FP2 data will
appear in a data table as –7999. If the data type is Long, NAN will appear in the data table as
–2,147,483,648.
Because NAN is a constant, it can be used in conjunction with the disable variable parameter
(
DisableVar
) in output processing instructions. Use variable = NAN in the
DisableVar
parameter to discard NANs from affecting the other good values.
9.3 Timekeeping
Measurement of time is an essential datalogger function. Time measurement with the onboard
clock enables the datalogger to run on a precise interval, attach time stamps to data, measure
the interval between events, and time the initiation of control functions. Details on clock
accuracy and resolution are available in the
System specifications (p. 162). An internal lithium
battery backs the clock when the datalogger is not externally powered (see Internal battery (p.
105)).
9.3.1 Clock best practices
When setting the clock with LoggerNet, initiate it manually during a maintenance period when
the datalogger is not actively writing to Data Tables. Click the Set button in the Clocks field of
the LoggerNet Connect Screen.
If you are going to use automated clock check with LoggerNet (clock settings can be found on
the LoggerNet Setup Standard View Clock tab). it is recommended that you do this on the order
of days (not hours). Set an allowed clock deviation that is appropriate for the expected jitter in
the network, and use the initial time setting to offset the clock check away from storage and
measurement intervals.
The amount of time required for a Clock Check command to reach the datalogger, be processed,
and for it to send its response is called round-trip time, or time-of-flight. To calculate an estimate
of this time-of-flight, LoggerNet maintains a history (in order) of the round-trip times for the ten
previous successful clock check transactions. It adds this average to the time values received from
the datalogger and subtracts it from any adjustment that it might make.
9.3.2 Time stamps
A measurement without an accurate time reference often has little meaning. Data collected from
dataloggers is stored with time stamps. How closely a time stamp corresponds to the actual time
9. Tips and troubleshooting 116