1. Basic Working Concept

When pressure is applied to a sensor:

➡️ It acts on a sensing element (diaphragm)
➡️ The diaphragm deforms (deflects)
➡️ This deformation is converted into an electrical signal

2. Main Components

1. Sensing Element (Diaphragm)

• Thin metallic or silicon membrane
• Deforms under applied pressure
• Common materials: Stainless Steel, Silicon, Ceramic

2. Transduction Element

Converts mechanical deformation into an electrical signal.

Types:

• Strain Gauge (most common)
• Capacitive
• Piezoelectric
• Piezoresistive

3. Signal Conditioning Circuit

• Amplifies weak signals
• Converts into standard output signals like:
  • 4–20 mA
  • Voltage output

3. Step-by-Step Working

Step 1: Pressure Application

• Process pressure (P) is applied through a sensor port

Step 2: Diaphragm Deflection

• Pressure causes the diaphragm to bend
• Deflection is proportional to applied pressure

4. Common Working Mechanisms

✅ A. Strain Gauge Type (Most Widely Used)

• Strain gauges are mounted on the diaphragm
• When deformation occurs:
  • Length and cross-section change
  • Electrical resistance changes

Principle:
R = ρ (L / A)

• Change in resistance is very small
• Measured using a Wheatstone Bridge

Output:

• Resistance change → Converted into voltage signal

✅ B. Capacitive Pressure Sensor

• Uses two plates:
  • One fixed
  • One movable (diaphragm)

Principle:
C = ε (A / d)

• Pressure change alters distance (d)
• Capacitance changes accordingly

✅ C. Piezoelectric Pressure Sensor

• Uses crystals like Quartz

Working:

• Pressure generates electric charge directly

Best For:

• Dynamic pressure measurement
• Vibrations and pulsations

✅ D. Piezoresistive (Silicon) Sensor

• Silicon diaphragm with embedded resistors
• Pressure → Stress → Resistance change

Key Feature:

• Very high sensitivity

5. Signal Conversion Process

1. Pressure → Mechanical deformation
2. Deformation → Electrical change (Resistance / Capacitance / Charge)
3. Electrical change → Amplified signal
4. Output → Standard industrial signal

6. Output Signals

Typical outputs include:

• 4–20 mA (industry standard)
• 0–10 V / 0–5 V
• Digital outputs (HART / Modbus)

7. Types of Pressure Measurement

✔ Gauge Pressure

• Measured relative to atmospheric pressure

✔ Absolute Pressure

• Measured relative to vacuum

✔ Differential Pressure

• Difference between two pressure points