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Our Speed Sensors

VR Sensor Models

Variable Reluctance speed sensors can sense a ferrous metal target and is ideal for use in all types of environments and user specifications. Options include hermetically sealed, cryogenic, high temperature, intrinsically safe and explosion proof. In addition to the more common VR sensors, MSI also offers an inductive type speed sensor for applications where magnets, rather than ferrous metal, will be sensed.

This series offers a low cost, high-value sensor option for applications without the severe environmental conditions and thermocycling of the Premium Series Sensors. Features includes welded connector, stainless steel fronts, and operation up to 450°F.
VR sensors with the ability to withstand high levels of abuse in cryogenics, high temperature and other severe environments and are ideally suited for providing trouble-free service in harsh environments. Standard models operational to 450°F. Includes Humbucking VR Sensors which offer resistance to electrical noise interference with little or no loss in signal strength.

This product family offers Variable Reluctance (VR) speed sensors that integrate dual windings within the sensor housing to provide redundant output capability, and are extremely popular in aerospace and other critical applications.

VR sensor with a broad temperature range of –450°F to +850°F continuously and 1000°F intermittently. Available with MIL series connector or thermocouple pigtail leads.
Amplified, or Active, VR sensors integrate a preamplifier/signal conditioner within the sensor housing and offer excellent noise immunity and greater transmission capability. An Amplified VR Sensor offers near-zero velocity (2 Hz) speed sensing, large air gap capability, and several digital output choices.

The DME series offers EMI (Electromagnetic Interference) susceptability hardening and improved performance in environments with greater external electrical noise and disruptions. The DME series is equivalent to the Honeywell 584xx series while also offering CE compliance and additional pulse output offerings.

MSI intrinsically safe sensors are certified for use in both North America (CSA with NRTL/C), Europe (ATEX compliant with 2014/34/EU), and IECEx to the most stringent requirements.

Principles of Operation

Variable Reluctance (VR) sensors offer a unique solution to many system measurement problems by providing an uncomplicated, accurate, reliable, versatile counting device.

A variable reluctance sensor is composed of a winding wound around a cylindrical magnetic material, typically made of some type of ferrous material that is referred to as a pole piece. A magnet is attached behind the pole piece, creating a magnetic field through the pole piece and winding. This magnetic field projects out from the pole piece front, also known as the sensor tip. When ferrous material passes through and disrupts this magnetic field, electricity (a sine wave) is generated. They are passive devices and do not require any external source of power to generate a signal.

Therefore, when the tip of the sensor is placed near a moving or rotating device made of ferrous metal such as a gear or rotor, a simple technique for measuring rotational speed is created. The frequency of the signal is directly proportional to the speed of rotation. The amplitude of the signal is affected by the speed of rotation, the material being sensed and the distance, known as the "air gap", between the sensor tip and the rotating object.

Most manufacturers of magnetic sensors base their design on having very small air gaps of .005" to .015". Increasing the size of this gap produces a fall-off of signal voltage. In practical application, such small gaps could be hazardous, especially if the object being sensed is not concentric or tends to have a loss of concentricity with increased speed or motion. MSI's Premium line of VR sensors employ a special "focusing tip" which enables the sensor to operate at larger gaps in excess of .060". The closer the sensor is to the object being sensed, the greater the amplitude. MSI sensors however, allow the sensor to be farther from the target without rapid signal deterioration as in other sensors.

Motion Sensors also manufactures a variation of variable reluctance sensors known as inductive magnetic sensors. These differ from standard VR sensors in that the magnet is not in the unit, but in the object being sensed. They are used when the rotating device sensed cannot be made of ferrous materials. For instance, if the target to be sensed is made of nonmagnetic stainless steel, brass, aluminum or plastic, a centerpole magnet may be placed in the center of the rotating device. Alternatively, magnets can be imbedded (equally spaced) into the target's outer rim or diameter. Inductive sensors will sense the magnetic fields and produce a signal. They are also designed to provide this capability at air gap distances substantially greater than standard VR sensors, as would be required for centerpole magnet locations.

In summary, variable reluctance sensors convert mechanical motion to electric energy without direct contact when positioned near a turning rotor, gear, shaft or other regularly moving device. The output signal can be fed into a digital counter, totalizer, analog converter, tachometer, overspeed or underspeed control, oscilloscope, or other monitoring and control device. The sensor provides a simple, reliable, inexpensive transducer for highly sophisticated control systems.

ATEX & IECEx Certified: Custom & Standard Speed Sensors for Intrinsically Safe applications (also approved by CSA w/NRTL/C)