Campbell Scientific CR1000KD CR800 and CR850 Measurement and Control Systems - Page 408
Measurements and NAN
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Section 10. Troubleshooting 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. 408