Bi-Metal Thermometer

Operating Principle

The Bi-Metal Thermometer operates on the principle of differential thermal expansion between two bonded metals. The bimetallic sensing element — a helical or spiral coil formed from two metals with differing coefficients of thermal expansion — deflects proportionally as temperature changes. This mechanical deflection is transmitted directly to the pointer, providing a clear, instantaneous local temperature reading without the need for external power.

Construction & Materials

The instrument is constructed entirely from stainless steel, ensuring durability and corrosion resistance in demanding industrial environments. The stem and case are fabricated from high-grade stainless steel (SS304/SS316), providing robust protection against moisture, chemicals, and mechanical stress. The dial face is clearly graduated and protected by a shatterproof glass or polycarbonate window, while the sealed enclosure meets IP65 ingress protection standards.

Connection Types

Two connection configurations are available to suit different installation requirements. The adjustable angle connection allows the dial to be rotated 360° and tilted to any angle, enabling optimal readability regardless of the mounting orientation. The bottom entry connection provides a fixed, straight configuration suitable for vertical installations in pipelines and vessels. Both types are available with standard ½" NPT or BSP process connections.

Temperature Range & Dial Sizes

The thermometer covers a wide measurement range of -40°C to +600°C, making it suitable for both cryogenic and high-temperature process applications. Three dial sizes are offered to accommodate varying visibility and installation space requirements:

• 80 mm — compact installations with limited panel space
• 100 mm — standard industrial applications
• 160 mm — large-scale or remote-reading installations requiring high visibility

Ingress Protection

The thermometer carries an IP65 ingress protection rating, confirming complete protection against dust ingress and resistance to low-pressure water jets from any direction. This makes it well-suited for outdoor installations, wash-down environments, and locations subject to condensation or splashing.

Typical Applications

The Bi-Metal Thermometer is widely deployed across a broad range of industries where reliable, maintenance-free local temperature indication is required:

• Oil & Gas — pipeline monitoring, wellhead equipment, separator vessels, and heat exchangers
• Chemical & Petrochemical — reactor vessels, storage tanks, and process lines handling aggressive media
• HVAC & Utilities — chilled water systems, boiler circuits, air handling units, and cooling towers

Its all-mechanical design eliminates the need for electrical connections or signal conditioning, reducing installation complexity and long-term maintenance costs.