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Filtering NaN values from SDI12 sensor in table averages


reinhu Dec 11, 2018 04:13 AM

Hi,

I'm building a program to log data from an SDI-12 sensor (acustic doppler). I expect that the sensor will return NaN values occacionally, and I would like these excluded from the average values. The behavior when just calling Average() with NaN values present is to return NaN. I tried a workaround where I only call the table when the value is not NaN. This can, however, result in the table not being called at the end of the DataInterval resulting in no values being written at all for that timestep. I would also like to report the number of values used in the average.

I've included my program below. Table1 is the default datatable. Here NaN's are written if one or more scans results in NaN values. Table3 is only called if the values are not NaN, and gives a usable average and a count of values used in the average. However, as the call is skipped if NaN is occuring at the end of the DataInterval then nothing is written to the table.

Is there a way to exclude NaN values from average and get a count of values used to construct the average?

In a case where all scans in a DataInterval return NaN I would also like a row to be written in Table3, can this be achieved?

 

'CR800 Series
'Created by Short Cut (4.0)

'Declare Variables and Units
Public BattV
Public PTemp_C
Public SDI12(4)
Public Counter_avg

Alias SDI12(1)=Depth
Alias SDI12(2)=Velocity
Alias SDI12(3)=Temperature
Alias SDI12(4)=Battery

Units BattV=Volts
Units PTemp_C=Deg C
Units Depth=mm
Units Velocity=mm/s
Units Temperature=Deg C
Units Battery=V
Units Counter_avg=Count



'Define Data Tables
DataTable(Table1,True,-1)
	DataInterval(0,5,Min,10)
	Average(1,Depth,FP2,False)
	Average(1,Velocity,FP2,False)
	Average(1,Temperature,FP2,False)
	Sample(1,Battery,FP2)
EndTable

DataTable(Table2,True,-1)
	DataInterval(0,60,Min,10)
	Minimum(1,BattV,FP2,False,False)
	Sample(1,PTemp_C,FP2)
EndTable

DataTable(Table3,True,-1)
	DataInterval(0,5,Min,10)
	Average(1,Depth,FP2,False)
	Average(1,Velocity,FP2,False)
	Average(1,Temperature,FP2,False)
	Sample(1,Battery,FP2)
	Totalize(1, Counter_avg, FP2, False)
EndTable

'Main Program
BeginProg
	Counter_avg = 1
	'Main Scan
	Scan(10,Sec,1,0)
		'Default CR800 Datalogger Battery Voltage measurement 'BattV'
		Battery(BattV)
		'Default CR800 Datalogger Wiring Panel Temperature measurement 'PTemp_C'
		PanelTemp(PTemp_C,_60Hz)
		'Generic SDI-12 Sensor measurements 'Depth', 'Velocity', 'Temperature', and 'Battery'
		SDI12Recorder(SDI12(),1,"0","M!",1,0)
		'Call Data Tables and Store Data
		CallTable Table1
		CallTable Table2
		' Only call Table3 if Depth and Velocity are not NaN
		If Depth <> NaN AND Velocity <> NaN then
			CallTable Table3
		EndIf
		
	NextScan
EndProg

 

Cheers


jtrauntvein Dec 11, 2018 12:23 PM

Take a look in the CRBasic help for the Average() output processing instruction.  The last parameter for this instruction is referred to as a disableVar and it serves the purpose of allowing an expression to control whether the current value should be stored.  It could be something as simple as:

   Average(1, Temperature, FP2, Temperature = NaN)

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