Campbell Scientific CS547A-L Conductivity/Temperature Probe and A547A Interface User Manual

Page 12

CS547A Conductivity and Temperature Probe and A547 Interface

'\\\\\\\\\\\\\\\\\\\\\\\\\\\ PROGRAM ////////////////////////////
BeginProg

'evaluate and edit each of these 3 user specific values

Rcable=25

'edit this value to the actual footage of cable on your sensor

CellConstant=1.50

'edit this value with the Cell Constant (Kc) printed

'on the label of each sensor

TempCoef=2

'see section 9 of the manual for an explanation of how

'to more precisely determine the value of this coefficient

Scan(5,Sec, 3, 0)

'make a preliminary measurement of resistance to determine best range code

BrFull(Rs, 1, mV2500, 1, VX1, 1, 2500, True, True, 0, 250, -0.001, 1)

1*Rs/(1.0-Rs)

'test the initial measurement to then make a more accurate measurement

Select Case Rs

Case Is < 1.8

BRHalf(Rs, 1, mV2500, 2, VX1, 1, 2500, True, 0, 250, 1, 0)

(Rs/(1-Rs))

Case Is < 9.25

BRFull(Rs, 1, mV2500, 1, VX1, 1, 2500, True, True, 0, 250, -0.001, 1)

Rs/(1-Rs)

Case Is < 280

BRFull(Rs, 1, mV250, 1, VX1, 1, 2500, True, True, 0, 250, -0.001, 1)

Rs/(1-Rs)

EndSelect

'Subtract resistance errors (Rp) caused by the blocking capacitors
'(0.005Kohm and the cable length (0.000032Kohm/ft)

Rp = -Rcable * (0.000032) – 0.005

Rs = Rs + Rp

'EC is then calculated by multiplying the reciprocal of the resistance,
'which is conductance, by the cell constant

OneOvrRs = 1 / Rs

Ct = OneOvrRs * CellConstant

'the following corrects for errors of ionization in the EC measurement

If (Ct < 0.474) Then

Ct = (Ct * 0.95031) - 0.00378

Else

Ct= -0.02889 + 0.98614 * Ct + 0.02846 * Ct

EndIf