Labs Idea #9: Milk Fat Concentration Sensor
Milk fat concentration of cow milk is measured on a routine basis in the laboratory. A disposable quick test would allow instant verification of milk fat content during milking.
Sensirion's flow sensor is a semiconductor MEMS version of the traditional hot wire anemometer. The sensing principle is based on thermal conductivity through the liquid or gas in contact with the wetted sensor surface (figure 2).
Thermal conductivity of a binary mixture of fat suspended in milk varies with its concentration. Sensirion's concentration sensor allows precise measurement of such variations in thermal conductivity subject to variations of milk fat concentration. Thus, Sensirion's flow sensor operates as concentration sensor in this application.
Bottles with different concentrations of fat in milk were prepared to test for concentration dependent differences in thermal conductivity Signal (figure 1). For the thermal conductivity measurement the sensor is dipped directly into the milk.
The measurement results demonstrate that Sensirion's flow sensor can be used as concentration sensor for variing milk fat concentrations (figure 3).
To build an own concentration sensor a Sensirion differential pressure sensor SDP6xx series (figure 4) can be sourced from distributors listed on the Sensirion website.
By careful breaking the inner plastic ring seal from the sensor's backside, the sensor chip is uncovered (figure 5-7).
Communicate with the digital sensor over I2C according to the explanations in the SDP600 series datasheet.
For concentration measurements a special command is required, which can be obtained from Sensirion.
Also other concentrations can be measured, e.g. urea concentration, helium concentration, etc..