The concentration calibration is organized in 6 layers. Figure 1. Concentration calibration layers 1 The information from the CCD element and the Pt-1000 temperature element. The position of the shadow edge is described by a number called CCD and scaled 0 … 100 %. For more information, see Figure 3 2 Sensor calibration: The actual refractive index nD is calculated from the CCD value. The process temperature is calculated from the Pt-1000 resistance. The sensor output is nD and temperature TEMP in degrees Celsius. The calibration process ensures same nD measurement performance for all sensors, making them interchangeable. The calibration of each sensor can be verified using standard refractive index liquids. 3 Chemical curve: The indicating transmitter DTR receives nD and TEMP and calculates the concentration value according to chemical curves. The result is a temperature-compensated calculated concentration value CALC. 4 Field calibration: Adjustment of the calculated concentration value CALC may be required to compensate for some process conditions or to fit the measurement to the laboratory results. The field calibration procedure determines the appropriate adjustment to CALC. The adjusted concentration is called CONC. If there is no adjustment, CALC and CONC are equal. Therefore the chemical curve is kept intact as a firm base for the calculation, the adjustment is merely additional terms. For more information, see Field calibration. 5 Damping: For more information, see Configuring output signal damping. 6 Output signal: The range of the 4 … 20 mA signal is defined by its 2 endpoints on the CONC scale. For more information, see Configuring mA outputs.