In bmcnellis/sapflux: Analyze Sapflux Traces

knitr::opts_chunk$set(fig.width = 8, fig.height = 5)

Seebeck Coefficients

Voltages from Type-T (copper-constantan) thermocouples are related to real temperatures through a physical phenomenon known as the 'Seebeck effect'. The relation is a simple coefficient, and is often present in datalogger software as a simple voltage multiplier. Within GranierConversions, the multiplier is used first for calculation efficacy, but a reference (i.e. ambient air at probe) temperature can also be supplied and temperatures calculated based on a regression of NIST table values.

typeT <- c(0.038748, 0.038815, 0.038884, 0.038953, 0.039024, 0.039095, 0.039168,
           0.039242, 0.039316, 0.039391, 0.039468, 0.039545, 0.039622, 0.039701,
           0.039780, 0.039859, 0.039939, 0.040020, 0.040101, 0.040183, 0.040265,
           0.040348, 0.040431, 0.040515, 0.040598, 0.040682, 0.040767, 0.040851,
           0.040936, 0.041021, 0.041106, 0.041192, 0.041277, 0.041363, 0.041449,
           0.041534, 0.041620, 0.041706, 0.041792, 0.041878, 0.041964)
estS <- vector(mode="numeric", length=41)
for (i in 0:40) {
  estS[i+1] <- sapflux:::CalcSeebeck(C = i)
}
compare <- cbind(0:40, typeT,estS)
colnames(compare) <- c('Reference junction temperature (deg C)',
                       'NIST table value', 'Estimated Seebeck coefficient')
rownames(compare) <- NULL
plot(x = 0:40, y = compare[, 2], col = "blue", 
     cex = 0.5, pch = 19,
     xlab = "Reference junction temperature (deg C)",
     ylab = "Seebeck Coefficient")
points(x = 0:40, y = compare[, 3], 
     cex = 0.5, pch = 19, 
     col = "red")
legend(15, 0.0395, c("NIST table value", "Regression-estimated value"),
     lty = c(1, 1), col = c("blue", "red"))