Passive Speed Sensor

Passive (VR)
Also refer to the 70085 Series

Control and protection circuits have relied on variable reluctance technology for years. With few components and no moving parts, the passive magnetic speed sensors can provide a signal from the inside of an aircraft engine at temperatures approaching 425 degrees C or from the hub of an automobile wheel at high shock and vibration. The advantage of these sensors are:

• High reliability
• Simple installation
• Long life due to no moving parts or contacts
• Self powered operation
• Wide variety of shapes and sizes
• Easy alignment
• Can be designed for almost any environment

Passive Speed Sensors: What They Are and Why They’re Essential

Passive speed sensors, often referred to as variable reluctance (VR) sensors, are compact, self-powering devices that detect rotational speed by measuring variations in magnetic reluctance. They generate an electrical signal automatically—no external power source needed—making them inherently reliable, robust, and ideally suited for harsh environments.

You need these sensors when accurate, low-maintenance speed monitoring is critical. Their simplicity, high-temperature resilience, and long lifecycle allow them to excel in applications from industrial flow measurement to safety systems in defense, where every rotation count matters.

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The Technology in a Nutshell

At the heart of a passive speed sensor lies a permanent magnet and coil assembly positioned close to a rotating ferrous target (like a gear tooth). As the target moves, each passing tooth alters the magnetic field, inducing a voltage pulse in the coil—simple electromagnetic induction. With no moving parts and minimal electronic complexity, VR sensors deliver:

• Self-powered operation, eliminating the need for auxiliary power.

• Exceptional shock and vibration tolerance, performing reliably even under extreme mechanical stress.

• High durability, ideal for high-temperature conditions—some models function inside aircraft engines or at hubs subjected to intense heat.

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Dive Into AI-Tek’s Passive Speed Sensor Portfolio

AI-Tek Instruments offers two standout product lines in passive VR sensors:

70082 Series

A versatile, widely deployed family of VR sensors. Designed for simple installation and broad compatibility, these sensors support a range of applications—from industrial machinery to precision system controls.

70085 Series

Engineered for high shock, vibration, and temperature environments. These models are frequently used in extreme settings—such as inside aircraft engines or on automotive hubs. They offer a wide array of specifications: varying thread lengths, output voltages, resistance, inductance, and operating temperatures (e.g., standard 40 V p-p output, DC resistance up to 130 Ω, operating from –55 °C to +107 °C).

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Key Applications: Water, Gas, and Military Emphasis

Water & Utility Sector

• Flow measurement in pumps and turbines: VR sensors ensure accurate rotational speed data needed for precise flow control and efficiency monitoring in water treatment facilities.

• Resistant to moisture and rugged conditions: Designed to withstand corrosive or damp environments, making them ideal for utility infrastructure.

Gas & Petrochemical Industry

• Pump and compressor monitoring: Critical for ensuring safe, continuous operation in gas distribution networks. Passive sensors can operate in explosive atmospheres (HAZLOC compliant) with no electronic failure points.

• Steam turbine speed control: Enhanced reliability under extreme temperatures ensures accurate feedback for safe and efficient turbine management.

Military & Defense Applications

• Armored vehicle systems, missile ground support equipment, and rotor/turbine control: AI-Tek’s compliance with AS9100 standards and focus on military-grade durability make these VR sensors a go-to solution for defense-critical speed sensing.

• Battlefield reliability: No external power, minimal failure points—perfect for scenarios where lives and mission success are at stake.