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Capacitance pressure transducers were originally developed for use in low vacuum research. Their capacitance charge exists from the movement of a diaphragm element which is usually metal-0n-metal coated quartz and is exposed to the process pressure on one side, and to the reference pressure on the other side. Depending on the type of pressure, the Capacitive transducer can be either absolute, gauge, or differential pressure transducer.  

Now the strain gauge pressure sensor on the other hand, consists of three basic elements, a force- gathering element (commonly a flexible diaphragm), which converts pressure into a measurable strain; strain gauge elements, which transform the strain into a proportional electrical signal; and the housing, which provides the required protection against environmental conditions and incorporates signal conditioning and mechanical and electrical.

Below are the pros and cons of each of these pressure sensors:

Variable Capacitance Pressure Switch:

Pros:

These are used in low vacuum research.

High Temperature applications.

Used as a secondary Standards especially in low-differential and lo-absolute pressure applications.

Cons:

Older units are more resistant to corrosion and are more sensitive due to vibration effects that used to cause Reading vibrations.

They have inherent limitations of mechanical motion-balance devices

Wheatstone bridge (Stain Based) Pressure Sensor:

Pros: These are true analog devices

They offer a wide operating temperature range

The sensors offer resolutions that is infinitely smooth

Thermal expansion of the diaphragm material does not affect the accuracy of the sensor.

Response to pressure is typically 1000 Hz or better for all strain gauge type.

Also offers fast thermal response because the active thermal compensation components and strain gauges can be bonded to the same thermal mass (the diaphragm and its side wall), resulting in reduced time lag during temperature changes.

Cons:

It requires a signal conditioning from a differential amplifier because the input and output grounds are different.

Lower pressures require the use of more expensive construction techniques, such as machined bending beams coupled with a bellows or convoluted sheet metal diaphragm. The signal level is another weak spot. As in all-metal gauges, the signal level of these sensors is low, usually a maximum of 30-40 mv of output at full scale for a 10 VDC input.

References:

Pressure Gauges & Switches. Retrieved September 01, 2018 from

https://www.omega.com/litrature/transactions/volue3/prssure.htm)links-to (Links to an external site.)Links to an external site. an external site.

Pressure Sensors. Retrieved September 01, 2018. From https://www.science direct.com/topics/chemistry/pressure-sensor.