In instrumentation, which of the following sensing principles are used in pressure sensors?

Introduction / Context:
Pressure measurement underpins process control, automotive systems, biomedical devices, and consumer electronics. Multiple transduction mechanisms exist, translating diaphragm deflection or volume change into an electrical signal usable by control systems and data acquisition hardware.

Given Data / Assumptions:

• We consider common industrial and embedded pressure sensors.
• Outputs may be resistive, capacitive, or via active electronics after conditioning.
• Mechanics include diaphragms, bellows, or aneroid capsules.

Concept / Approach:
Piezoresistive sensors mount strain gauges on a diaphragm; applied pressure changes resistance through strain, often used in silicon MEMS. Aneroid mechanisms convert pressure to displacement which can be read by a potentiometric element, producing a variable resistance output. Capacitive sensors measure the change in capacitance between plates as a diaphragm deflects, offering high sensitivity and low hysteresis. Each approach trades off sensitivity, temperature drift, linearity, and cost.

Step-by-Step Solution:
1) Recognize that piezoresistive (strain-gauge) is a mainstream method. 2) Identify aneroid + variable resistance as a valid mechanical-to-electrical conversion. 3) Confirm capacitive transduction as another standard technique. 4) Since all are used, select 'All of the above'.

Verification / Alternative check:
Sensor catalogs and application notes list piezoresistive and capacitive as dominant; aneroid mechanisms appear in gauges and legacy industrial transmitters with potentiometric readouts.

Why Other Options Are Wrong:
Options A/B/C individually are true but incomplete; the question asks which are used broadly.
Option E is invalid because multiple methods are indeed used.

Common Pitfalls:
Assuming a single 'best' technology; environment (temperature, media compatibility, EMI) often dictates the choice.

Final Answer:
All of the above