In a system with a capacitance pressure sensor, what is applied to the isolating diaphragm?

In a capacitance pressure sensor, the isolating diaphragm is designed to be in direct contact with the pressure to be measured. The diaphragm flexes in response to the applied pressure, which alters the distance between the capacitor plates, thereby changing the capacitance. This change in capacitance is then converted into an electrical signal that corresponds to the pressure being measured.

The reference pressure, ambient pressure, and atmospheric pressure do not apply directly to the diaphragm in the same way. Instead, those pressures are typically used in relation to the overall system calibration or for reference points in pressure measurements, but they are not the direct input that interacts with the diaphragm of the sensor. Thus, the correct answer regarding what is applied to the isolating diaphragm in a capacitance pressure sensor is the pressure to be measured.