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Pressure sensor's function is based on physical phenomenon. It can be used at least two different situation:
water, air or between two points of measurement.

Table of Contents

Types of pressures and basic physics of pressure sensing

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where P is the pressure (Pa), F is the force (N) and A is the area (m²). [1]

Force unit can be determined by F= m*a, (mass*acceleration).

Volume pressure, known as the density can be used when determining the volume of the container.

p (rho) = m (mass) / V (volume). [2.]

Archimedes's principle states can be determined by for example a person goes bath and the waterspills over bathtub. The amount of spilled
water has the same volume than a person.

Physical formula is: P= p*h*g

P = p (rho) * h (height in metres) *g (gravitation force (9,81 m/s^2))

Pascal's law states that an increase in pressure at any point in a liquid causes a corresponding increase at every other point in the
liquid. [32.]

For example if pressing a cylinder on the other side and because of the water is solid, second cylinder will be pulled out upward.

This method is a common in for example car brakes.

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Gauge pressure measurement is a subtype of differential pressure measurement. The idea is to compare pressure at any point to the current atmospheric pressure. The Gauge pressure measurement is not consistent because the atmospheric pressure varies with altitude so it cannot be used in critical measurements. Still gauge pressure sensors are used in tire pressure and blood pressure measurements. [41.]

Where to use pressure sensors?

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- Marine Industry: Especially on submarines it is very precise how much oxygen the crew has; pressure sensors regulate the amount. [41.]

Piezoelectric transducers

We chose as our Piezoelectric sensor a PiezoStar® Pressure Sensor Type 6125C. [6](3)

Transfer function

Transfer function for piezoelectric transducer can be calculated as:

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There are different kind of sensors on the market with different amount of bars. New piezo materials (PiezoStar crystal) inprove the sensors performance. [63.]

Other Characteristics

Operating temperature range -20...350 C
Measurin range 0...300 bar
Natural frequence >70 kHz [63.]

Conducting for piezoelectric transducers

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The system has some output noise which is approximately some hundreds of nV/sqrt(Hz). Noises are coming from voltage and current. [85; 9.6] 

Piezoelectric sensors are usually very stable so they don't need calibration after purchasing but in extreme conditions characteristics may change over time. In this case the sensors are usually sen to the manufacturer. [10; 11]

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