SmCo Magnets for Gas Turbine Speed Sensors: Engineering & Selection Guide

Gas turbine speed sensors (both Variable Reluctance and Hall Effect) operate in some of the most punishing thermal and vibrational environments in modern engineering. While NdFeB magnets fail rapidly above 150°C, Samarium Cobalt (SmCo) provides the necessary thermal headroom.

However, simply specifying "SmCo" on a drawing is not enough. Without precise grade mapping, irreversible flux loss and mechanical chipping will lead to sensor drift or catastrophic failure.

The Failure Matrix: Why Turbine Sensors Drift

Before grade selection, engineering teams must understand the root causes of signal degradation in high-speed turbine environments.

Sensor Design Decision Tree (Visual)

Use this logic flow to lock your baseline assumptions before issuing an RFQ.

Grade Selection: SmCo5 vs Sm2Co17 in Turbines

For gas turbine speed sensors (often mounted directly on the gearbox or compressor casing), the ambient temperature frequently exceeds 200°C, with thermal soak back pushing temperatures even higher after shutdown.

1. Sm2Co17 (2:17) is the industry standard for aerospace and industrial heavy-duty turbines. It offers an operating ceiling of 300°C to 350°C and a significantly higher Br (Remanence), allowing for a stronger signal output in Variable Reluctance (VR) sensors which rely on magnetic flux crossing the air gap to the gear teeth.
2. SmCo5 (1:5) is typically reserved for auxiliary speed sensors positioned further from the hot section (e.g., < 200°C), where its superior corrosion resistance without coating may provide a cost advantage, or where extreme miniaturization requires slightly better machinability without chipping.

RFQ Checklist for Turbine Speed Sensor Magnets

To eliminate back-and-forth guessing and secure accurate DFM (Design for Manufacturability) feedback from SmCoSupply, include this specific data in your initial inquiry:

• Continuous and Peak Temperature: Crucial for identifying the correct intrinsic coercivity (Hcj) margin.
• Air Gap Flux Requirement: State the required Gauss/Tesla at the sensor tip, not just the raw magnet grade.
• Geometry and Edge Prep: Specify mandatory chamfers (e.g., 0.2mm x 45°) on all edges. Sharp edges on SmCo will micro-fracture under turbine vibration, creating loose magnetic debris in the housing.
• Pre-Aging Requirements: If your sensor demands zero irreversible loss post-assembly, specify thermal stabilization requirements (e.g., exposing the magnet to 250°C for 24 hours prior to calibration).

Mechanical Integration & Encapsulation

Because Samarium Cobalt is highly brittle, it should never be press-fit directly into a metal sensor housing without compliance.

• Laser Welding / Sealing: Most turbine speed sensors use a stainless steel or Inconel sleeve that is laser-welded shut. The SmCo magnet is housed inside, protected from both mechanical shock and corrosive turbine fluids (Skydrol, jet fuel, synthetic oils).
• Potting: High-temperature epoxies or potting compounds are used to secure the magnet within the sleeve, damping high-frequency casing vibrations.

Next Steps

Validating a new gas turbine speed sensor takes months of thermal cycle testing and qualification. Do not risk your project timeline by testing inadequate grades.

Bring your operational envelope to the engineers at SmCoSupply. We will map your temperature and signal requirements directly to a proven Sm2Co17 or SmCo5 grade, complete with tolerance risk-control.

Contact Engineering for Grade Mapping