PrayogSetu VIRTUAL LAB

Department of Instrumentation & Control Engineering • Primary Sensing Elements

INSTRUMENT Bellows Pressure Sensing Element
PRINCIPLE Pressure → Mechanical Displacement
AT REFERENCE (0.00 bar)

Bellows Mechanical Cross-Section

ZERO POSITION POSITION: 0.00mm BELLOWS DISPLACEMENT SCALE (mm) 0 2 4 6 8 10 PRESSURE INLET FIXED SUPPORT CORRUGATED BELLOWS MOVING END PLATE PUSH ROD PRESSURE CHAMBER
MECHANICAL SENSING SIGNAL CHAIN
PROCESS PRESSURE
0.00 bar
BELLOWS DEFORMATION
0.0 %
MECHANICAL DISPLACEMENT
0.00 mm
Mode 1 (Vary Pressure): Keep the sensing range fixed and adjust process pressure from 0 to full-scale to observe proportional bellows deformation.
SENSING RANGE SELECTOR
APPLIED PROCESS PRESSURE
0 25% 50% 75% 100%
bar
PRESETS:
ANALOG PRESSURE GAUGE
0.00 bar
SENSED DISPLACEMENT
0.00 mm
APPLIED PRESSURE
0.00 bar
BELLOWS DISPLACEMENT
0.00 mm
PRESSURE %
0.0 %
SENSING RANGE
0 – 10 bar
REFERENCE POSITION
0.00 mm
CURRENT POSITION
0.00 mm

LIVE GRAPH: Pressure vs Bellows Displacement

Idealized Mechanical Relationship: $\Delta x \propto P$

EXPERIMENT OBSERVATION TABLE

Trial # Applied Pressure (bar) Pressure (%) Bellows Displacement (mm) Mechanical Position (mm) Sensing Range
No readings recorded yet. Adjust pressure and click [ ADD CURRENT READING ].

GUIDED LABORATORY PROCEDURE

THEORY & ENGINEERING REFERENCE

1. What is a Bellows Pressure Sensing Element?

A Bellows Pressure Sensing Element is an elastic, thin-walled metallic tube manufactured with deep circumferential accordion-like folds (corrugations). It acts as a Primary Pressure Sensing Element that converts fluid pressure directly into linear mechanical displacement.

2. Principle of Operation & Governing Equations

When fluid pressure (P) is applied inside or surrounding the bellows capsule, an axial force (F) is exerted upon the Moving End Plate:

F = P × Ae

where Ae is the effective surface area of the bellows folds. This axial force deforms the corrugated metallic walls, producing linear mechanical displacement (Δx) against the inherent elastic stiffness (Kb) of the metal:

Δx = (P × Ae) / Kb

In an idealized model, displacement Δx is strictly proportional to applied pressure P, producing a linear response across the operational range.

3. Materials & Construction

Bellows are seamlessly formed or welded from highly flexible, fatigue-resistant alloys:

  • Phosphor Bronze: Excellent elasticity for low to medium pressure ranges.
  • Stainless Steel (316L): High corrosion resistance for aggressive chemical process media.
  • Beryllium Copper: Maximum hysteresis resistance and high cycle life.
  • Monel / Inconel: High-temperature and extreme pressure applications.