Campbell Scientific CS547A-L Conductivity/Temperature Probe and A547A Interface - Manual (Page 11)

CS547A Conductivity and Temperature Probe and A547 Interface
2. Correction of ionization errors in EC measurements
Ionization caused by the excitation of the EC sensor can cause large
errors. Campbell Scientific has developed a linear correction for
conductivity between 0.005 and 0.44 mS cm
-1 , and a quadratic correction
for conductivity between 0.44 and 7.0 mS cm -1 . Corrections were
determined in standard salt solutions containing KCl, Na
2
SO
4
, NaHCO
3
,
and NaCl.
3. Correction of temperature errors in EC measurements
The effect of temperature on the sample solution can cause large errors in
the EC measurement. A simple method of correcting for this effect is to
assume a linear relationship between temperature and EC. This method
generally produces values to within 2% to 3% of a measurement made at
25°C.
The best corrections are made when the temperature coefficient is
determined at a temperature near field conditions. See Section 9 for
details on how to determine the temperature coefficient. If determining
the temperature coefficient is not possible, use a value of 2%/
°C as a
rough estimate.
4. Output processing
Over large ranges, EC is not linear and is best to use the Sample
instruction in CRBasic or Instruction 70 in Edlog. In limited ranges,
averaging measurements over time may be acceptable; this is
accomplished by using the Average instruction in CRBasic or Instruction
71 in Edlog. Convention requires that the temperature at the time of the
measurement be reported.
5.2 Example Measurement Programs
5.2.1 CRBasic
'Program name: CS547A.CR1
'\\\\\\\\\\\\\\\\\\\\\\\\\ DECLARATIONS /////////////////////////
Public Rcable, Rp, CellConstant, TempCoef
Public Rs, Ct
Public TempDeg_C
Public C25mScm_1
Dim OneOvrRs, Ct100, A, TC_Proces
'\\\\\\\\\\\\\\\\\\\\\\\\ OUTPUT SECTION ////////////////////////
DataTable (ECSample,True,-1)
DataInterval (0,60,Min,10)
Sample (1,Ct,FP2)
Sample (1,TempDeg_C,FP2)
Sample (1,C25mScm_1,FP2)
EndTable
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