Campbell Scientific CR9000X Measurement and Control System - Manual (Page 75)

Section 2. Data Storage and Retrieval
2.2.1 NAN and ±INF
NAN (not-a-number) and ±INF (infinite) are data words indicating an
anomaly has occurred in datalogger function or processing. NAN is a
constant that can be used in expressions such as shown in Example 2.2-1.
If WindDir = NAN Then
WDFlag = True
Else
WDFlag=False
EndIf
EXAMPLE 2.2-1. Using NAN in an Expressions
NAN can also be used in the disable parameter in output processing
instructions. For example, using the following syntax, any NANs would
not be included in the average compilation.
Average(1,Source,FP2,Source=NAN).
2.2.1.1 Analog Measurements and NAN
NAN indicates that an operation or instruction failed to return a valid
result.
When NAN results from analog voltage measurements, it indicates an
voltage over-range error wherein the input voltage exceeds the
programmed input range.
If an analog channel is open (inputs not connected but “floating” or
broken), the inputs can remain floating near the voltage that they were last
connected to or they can gradually build up a static charge. This can result
in a measurement result of NAN or a measurement reading that looks good,
but is erroneous. In addition, sensors that have a floating output (output is
not referenced to a ground, such as a thermocouple) can float out of range
of the logger's operational voltage limits resulting in a measurement result
of NAN.
See Section 3.1.2.2 Differential Voltage Range for information on using
the C option on range codes to null the static charge.
To make a differential measurement, voltage inputs must be within the
CR9000X operational input voltage limits of ±5 V. If either the high side
or the low side of a differential measurement is outside of this range, either
a NAN or an erroneous value can be returned by the measurement.
See Section 3.1.2.2 Differential Voltage Range for information on the R
option used on Range Codes to insure that NAN is returned rather than an
erroneous result.
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