Hardware
- S2GO PRESSURE DPS422 Evaluation Board
- PSoC 6 BLE Pioneer Kit CY8CKIT-062-BLE
Reference
Project Link
Operating Principle of the Sensor
DPS422 makes use of a capacitive measurement principle. The sensor elements consist of a number of sealed vacuum cells. Each cell consists of a hollow, evacuated cavity with a flexible membrane sealing the top. The top membrane and the bottom of the cell are electrodes, which form a capacitor. Due to the pressure difference between the interior of the cell and the ambient environment, the top membrane is deflected towards the bottom of the cell. The vacuum cells are combined in a parallel measurement configuration, to increase the sensitivity and noise performance of the DPS422. Increasing ambient pressure causes greater deflection towards the bottom of the cell and hence and increase in the capacitance between the membrane and the bottom of the cell. Decreasing ambient pressure reduces the deflection of the membrane and reduces the capacitance between the membrane and the bottom of the cell. Pressure measurement is carried out by measuring the capacitance between the top and bottom of the cells and applying a calculation to the capacitance result to determine the pressure in Pa. It is also required to include a temperature correction in this calculation to eliminate temperature drift from the output.
- Temperature Measurement :
The DPS422 temperature measurement uses a silicon bandgap temperature sensor, measuring the base-emitter voltage (Vbe) of two BJT transistors, biased at different currents (IC1 and IC2). This measurement is used at a system level in the pressure output calculation to correct any temperature related measurement drift. The temperature of the transistors can be accurately determined by measuring the difference in voltage between both and applying the formula:
∆𝑉𝐵𝐸 = ((𝐾 × 𝑇) ÷ 𝑞) × ln(𝐼𝐶1 ÷ 𝐼𝐶2)
Where
T is the temperature in Kelvin
K is Boltzmann's constant and
q is the charge of a single electron.
For step by step calculation of pressure and temperature values, refer to section 5.1.1 and 6.1 - 6.3 respectively, of the datasheet.
