Example 21: corr_cond3 - Conductivity corrections for RBRLegato and 6000dbar C and CT cell

With the RBRlegato³ C.T.D logger, the conductivity reading from the conductivity channel without corrections is given by a simple linear function:

$//<![CDATA[ \begin{array}{l}Craw = c_0 + c_1 \cdot c_2 \cdot R\end{array} //]]>$

where R is the normalized voltage ratio from the channel monitoring conductivity, c0,c1 are the core coefficients of the linear equation, along with c2 which is a geometrical factor (K-factor) reflecting the final installation of conductivity cell, 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:

$//<![CDATA[ \begin{array}{l}Corr = \dfrac{Craw - Kc_1 \cdot (Tcond - Tcal)}{1 + Kc_2 \cdot (Tcond - Tcal) + ( Kp_1 \cdot (Pcorr - Pcal) + Kp_2 \cdot (Pcorr - Pcal)^{2} + Kp_3 \cdot (Pcorr - Pcal)^{3}) }\end{array} //]]>$

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

$//<![CDATA[ \begin{array}{l}Corr = \dfrac{Craw - x_0 \cdot (value(n_0) - x_5)}{1 + x_1 \cdot (value(n_0) - x_5) + (x_2 \cdot (value(n_1) - x_6) + x_3 \cdot (value(n_1) - x_6)^{2} + x_4 \cdot (value(n_1) - x_6)^{3})}\end{array} //]]>$

where

• Craw is the uncorrected conductivity, c0  +  c1 × c2 × R,
• x0, x1 correspond respectively to the temperature compensation constants "Kc1", "Kc2"
• x2, x3, x4 correspond respectively to the pressure compensation constants "Kp1", "Kp2", "Kp3"
  
• x5 is the calibration temperature "Tcal" in °C,
• x6 is the calibration pressure "Pcal" in dbar,
  
• n0 is the index of the internal temperature of the conductivity cell channel, in this example 7,
  value(n0) is the final output value of the internal temperature of the conductivity cell 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. 

It is quite common to have a logger monitoring conductivity and temperature without a pressure channel, typically deployed at a known, constant depth. In this case, n1 would be set to "value", and so value(n1) would be substituted by a default value (see the "settings pressure" command).

Examples

Confirm the channel type.

Set the core coefficients.

Set the cross-channel correction coefficients.

Request confirmation of all calibration coefficients.