Campbell Scientific CR800 and CR850 Measurement and Control Systems - Manual (Page 408)

Section 10. Troubleshooting
408
results can be difficult due to the multitasking nature of the logger, but it can be a
useful tool for fine tuning a program.
10.3.4 NAN and ±INF
NAN (not-a-number) and ±INF (infinite) are data words indicating an exceptional
occurrence in datalogger function or processing. NAN is a constant that can be
used in expressions as shown in CRBasic example Using NAN in Expressions
(p.
408).
. NAN can also be used in conjunction with the disable variable ( DisableVar )
in output processing (data storage) instructions as shown in CRBasic example
Using NAN to Filter Data
(p. 410).
10.3.4.1 Measurements and NAN
A NAN indicates an invalid measurement.
10.3.4.1.1 Voltage Measurements
The CR800 has the following user-selectable voltage ranges: ±5000 mV, ±2500
mV, ±250 mV, ±25 mV, ±7.5 mV, ±2.5 mV. Input signals that exceed these
ranges result in an over-range indicated by a NAN for the measured result. With
auto range to automatically select the best input range, a NAN indicates that either
one or both of the two measurements in the auto-range sequence over ranged. A
voltage input not connected to a sensor is floating and the resulting measured
voltage often remains near the voltage of the previous measurement. Floating
measurements tend to wander in time, and can mimic a valid measurement. The
C (open input detect/common-mode null) range-code option can be used to force
a NAN result for open (floating) inputs.
10.3.4.1.2 SDI-12 Measurements
NAN is loaded into the first SDI12Recorder() variable under these conditions:
• When busy with terminal commands.
• When the command is an invalid command.
• When the sensor aborts with CR LF and there is no data.
CRBasic EXAMPLE. Using NAN in Expressions
CRBasic Example 67. Using NAN in Expressions
If WindDir = NAN Then
WDFlag = False
Else
WDFlag = True
EndIf
10.3.4.2 Floating-Point Math, NAN, and ±INF
Table Math Expressions and CRBasic Results
(p. 409)
lists math expressions, their
CRBasic form, and IEEE floating point-math result loaded into variables declared
as FLOAT or STRING.