Advanced Terminology and Functional Analysis of Pressure Switches in Industrial Automation
Opinion | Apr. 28th, 2025
David Carter
Pressure Product Line Manager
This article provides a systematic examination of pressure switch nomenclature, operational parameters, and classification criteria based on IEC 60947-5-1 and ASME B40.3 standards.
Pressure switches remain critical components in modern industrial control systems, serving as essential safeguards in fluid power, HVAC, and process engineering applications.
Fundamental Definitions
A pressure switch (PSW) is defined as a binary sensing device that opens or closes electrical contacts when a predetermined fluid pressure (gas or liquid) reaches its set point. Unlike pressure transducers, PSWs operate as discrete-state devices with inherent hysteresis (differential between activation and reset points) to prevent contact chatter.
Key terminologies:
Electromechanical Switches
- Diaphragm Actuated: Corrugated metal diaphragm (0.1-0.3mm) with ±0.5% repeatability
- Piston-Type: Stainless steel piston with PTFE seal for high-viscosity media (up to 5000 cSt)
- Bourdon Tube: Designed for pressures >1000 psi, with Class 1A (±1%) accuracy
Solid-State Switches
- MEMS-based piezoresistive sensors with integrated ASIC for temperature compensation
- Digital interfaces (IO-Link, Modbus RTU) for programmable deadbands (0.1-20% FS)
Critical Performance Parameters
- Hysteresis Adjustment:
- Mechanical spring preload (coarse)
- Magnetic damping (fine, ±2% FS)
- Electrical Ratings:
- Contact: SPDT/DPDT, gold-clad AgNi (10^6 cycles @ 250VAC/5A)
- IP/NEMA: IP67 or NEMA 4X for washdown
Failure Modes
- Stiction: Diaphragm adhesion in viscous media (mitigated by Teflon® coatings)
- Contact Welding: Arc suppression (RC snubbers)
- Creep: Plastic deformation under sustained pressure
Application-Specific Designs
- Differential Pressure Switches:
- Dual-port, measuring ΔP (0.1-15 psi)
- Applications: HVAC, hydraulic filtration
- Vacuum/Pressure Combination Switches:
- Bidirectional sensing (-30 inHg to +30 psi)
- Certified SIL 2 (IEC 61508) with redundant MEMS sensors
- Intrinsically Safe (IS) Models:
- FM/ATEX-approved, energy-limiting barriers
- Max spark energy: 20 μJ (Group IIC, hydrogen)
Calibration & Standards
- Traceability:
- ASME B40.3, ±0.25% FS accuracy, NIST-traceable deadweight testers
- Operational temp: -20°C to 85°C
- Industry Certifications:
- Food: 3-A (Ra ≤0.8 μm)
- Marine: DNV-GL approval for salt spray
- Oil & Gas: API 6A (10,000 psi)
Emerging Technologies
- Smart Pressure Switches:
- HART® 7.3 transmitters, predictive maintenance
- DIN 43650, OLED diagnostics
- Redundant Architectures:
- 2oo3 voting (IEC 61511 SIL 3)
- Cross-validated MEMS and strain gauges
Case Study: Offshore Drilling Choke Valve Control
- Dual-redundant PSW monitors hydraulic pressure (0-5000 psi) in subsea blowout preventers
- Sensors:
- Primary: 316L stainless steel diaphragm, Inconel® 718 spring
- Secondary: Silicon-on-sapphire MEMS, 0.05% FS/month drift
- Safety Logic: 1oo2D architecture (IEC 61508)
Anwoll pressure switch
Anwoll is a leading developer of pressure measurement and applications, with a mature series of pressure switches suitable for daily and cutting-edge applications.
If you would like to learn more about our pressure switches, please contact us directly.
