QSU - Fdom conversions

qsu_standard_conversions.r

## The limits of the instrument (milivolts) and the sensor (QSU)
mv_conv <- data.frame(mv_limits = c(10.85, 4965),qsu_limits = c(0,200))
## Plot the raw data to get an idea of what is hapenning
plot(qsu_limits~mv_limits, mv_conv, xlab="mV (datalogger)", 
     ylab = "Sensor limits (QSU)")
## Fit a model of the relationship
mv_conv_mod <- lm(qsu_limits~mv_limits, mv_conv)
## Add the trend model to the plot
abline(mv_conv_mod)
## An example to estimate the mV (Should be close to 100 QSU.)
predict(mv_conv_mod, data.frame(mv_limits = 2500))

## To correct for the sensor offset.
qsu.df <- data.frame(measured_conc = c(6.9, 130),
          stand_conc = c(15, 150))
## Fit a model to the ratio between the measured QSU and the factry QSU
qsu_offset_conv <- lm(stand_conc~measured_conc, qsu.df)
## convert the measured QSU to the factory QSU 
predict(qsu_offset_conv, data.frame(measured_conc= 6.9))


## Combining them together.

qsu_measured <- predict(mv_conv_mod, data.frame(mv_limits = 10:4965))
plot(predict(qsu_offset_conv, data.frame(measured_conc= qsu_measured)))