Strange readings using the 180 degree sensor on the EVAL-CN0409-ARDZ

Hi, during our master thesis we are testing different methods for preforming turbidity measurements on concrete slurry water.  When doing tests on the CN0409 we expect the 180 degree measurement to decreases when the slurry concentration increases, according to the Beer-Lambert Law. This is however not the case using our setup, between the concentration 0.4 and 0.6 the measured value are increasing. We are wondering if it's some error in the hardware, software or anything else?

(We have made 180 degree measurements using a cheaper sensor in combination with Arduino, and those results follows the Beer-Lambert Law.)

We are using EVAL-CN0409-ARDZ in combination with EVAL-ADICUP360.
The code is taken from https://github.com/analogdevicesinc/EVAL-ADICUP360/tree/master/projects/ADuCM360_demo_cn0409, with the small modification that the sensor readings are sent using AppPrintf(). This is done in the function CN0409_CalculateRawData() in src/CN0409.c using au16DataSlotA[u8Count] and au16DataSlotB[u8Count].

A plot of the sensor readings as well as photos of the different concentrations are included below.

Sensor readings:

Concentrations:



Image didn't show, made it smaller
[edited by: Karlsson at 12:30 PM (GMT -4) on 12 Apr 2021]