Conductivity - corrected for temperature and pressure

Let us consider a conductivity sensor integrated on the RBRconcerto³ C.T.D. The conductivity reading from Channel-1 without corrections is given by a simple linear function:

\[Craw = c_0 + c_1 \cdot R\]

where R is the normalized voltage ratio from Channel-1 monitoring conductivity, c0,c1 are the core coefficients of the linear equation, and Craw is the uncorrected conductivity output, reported in mS/cm for RBR marine instruments.

The equation which corrects the output for the effects of both temperature and pressure on the conductivity cell is:

\[Corr = \dfrac{Craw - Kc_1 \cdot (T - Tcal)}{1 + Kc_2 \cdot (T - Tcal) + Kc_3 \cdot (Pcorr - Pcal)}\]

Casting the equation into the style used by the logger would give:

\[Corr = \dfrac{Craw - x_0 \cdot (value(n_0) - x_3)}{1 + x_1 \cdot (value(n_0) - x_3) + x_2 \cdot (value(n_1) - x_4)}\]

where

  • Craw is the uncorrected conductivity, c0 + c1 × R

  • x0 , x1 , x2 correspond directly to the constants "Kc1", "Kc2" and "Kc3"

  • x3 is the calibration temperature "Tcal" in °C

  • x4 is the calibration pressure "Pcal" in dbar

  • n0 is the index of the temperature channel, in this example 2

  • value( n0 ) is the final output value of the temperature channel in °C

  • n1 is the index of the pressure channel, in this example 3
    value( n1 ) is the final output value of the pressure channel in dbar

  • Ccorr is the corrected output in mS/cm