SEN0604 sensor (4-in-1 Soil Moisture, Temperature, pH & EC Sensor).

Hi,
I have some questions about the SEN0604 sensor (4-in-1 Soil Moisture, Temperature, pH & EC Sensor).
I tried to look online for the technical details and the materials used in this sensor.
How is the pH measured? Does it use conductivity, or a special electrode? I saw one electrode is darker than the others — what material is it?
Is the temperature measured with an RTD?