Figure 1. A reliable measuring system must be capable of operating in environments of extreme stress. Source: Kaman

Sensors play an integral role in ensuring the safe and efficient operation of virtually every piece of industrial machinery. They are especially critical, however, in highly sensitive systems — like rockets, jet and turbine engines, nuclear reactors, subsea production systems and more — where even small deviations from normal operation can result in catastrophic losses. These industries are continuously bolstering their performance requirements, meaning that the solutions driving these systems need to stay ahead of the curve in terms of safety and reliability.

These applications are especially challenging in that they require sensors to operate reliably under extremely harsh conditions, including high and low temperatures, high pressures and potentially corrosive environments. Since the overall industry trend is aiming toward more robust and substantial product performance testing and monitoring, demand for sensors that can reliably measure position and displacement in extremely harsh environments is only going to increase. Sensors that are rugged and durable in these environments are the sole solution to surpass other existing options in the market that may not be suited for the toughest applications.

Measurement in extreme environments

When it comes to difficult environments, two primary sensor technologies are used to measure position or displacement: capacitive and inductive. Each technology has distinct advantages and disadvantages and distinguishing between the two is what will reveal the best sensor options.

Capacitive sensors operate on the principle of capacitance changes between the sensor and target — that is, the object being measured — to determine distance. Capacitive sensors perform well with many different materials. They also have the advantage of a relatively small spot size and are not sensitive to material thickness. They do require a target grounded to the measuring system, which is generally not a problem and can be constructed of very high temperature materials for operation at temperatures of approximately 2,100° F. The main disadvantage of capacitive sensors is their sensitivity to humidity changes, fluids or environmental contaminants. While they can be used in extreme conditions, the environment must be clean.

Inductive sensors, also referred to as eddy current sensors, operate by generating eddy currents in a target material. These sensors require a conductive target, which is a bit more limiting than capacitance technology, but a ground connection between the target and measuring system is not necessary. Sensor performance is affected by target material conductivity and the sensor must be calibrated to the specific material it will measure in the application. These sensors have a larger spot size in comparison to other technologies, which makes them insensitive to material finish. Performance is also affected by temperature changes. This must be taken into account during the calibration process. One main advantage is that inductive sensors can operate in the presence of, or be totally submerged in, fluids and environmental contaminants. In general, non-conductive material between the sensor and the target is not detected.

Extreme environment series

Kaman Precision Products manufactures a line of high-precision sensors and systems specifically for extreme environment applications. These include three displacement measuring systems, all able to operate at high temperatures.

The high temperature products were initially designed for NASA and the nuclear power industry; applications all requiring high reliability, accuracy and structural integrity. The same engineering skill and technology that went into Kaman’s microphone for measuring the dB level of jet engine exhaust noise, in the exhaust, went into the design and manufacture of this line of high temperature products. For reference, this microphone is designed to withstand temperatures well over 2,000° F.

The extreme environment series is designed for both cryogenic and high temperature applications, as well as moderate pressure environments. These sensors find extensive use in the energy market, specifically in power generation applications ranging from traditional fossil fuel power generation to nuclear operations.

A specific application excellent for these sensors is the measuring of nuclear fuel rod position and vibration,Figure 2. Kaman can customize sensors to fit specifications of virtually any application. Source: Kaman as the inductive sensors are unaffected by radiation and most other environmental contaminants. Additionally, they are used in the development and test of cryogenic turbomachinery for rocket engines, as well as a myriad of industrial applications and research and development purposes.

Extreme environment series sensors provide up to 1,000° F of precise measurements at continuous operation, and over 1,200° F for short-term operation. They can withstand pressures up to 5,000 psi. Resolution and repeatability are comparable to Kaman’s conventional line of high-precision systems. The materials of construction include high-temperature transducers made with hermetically sealed, all laser-welded Inconel housings, along with metal-jacketed, mineral-insulated cables.

AMS-3946 series

The AMS-3946 non-contact, high-precision proximity measuring system is part of Kaman’s AMS-3000 series of sensors. In 2021, the AMS series was named a winner in the data acquisition and analytics category at the Best of Sensors awards. The AMS series is widely recognized across the industry for its reliable performance in high-pressure environments of over 5,000 psi.

With the AMS-3946, Kaman has pushed the envelope further by designing a measuring system capable of operating in environments with pressures up to 40,000 psi. These types of extremely harsh conditions are often seen in subsea oil and gas applications. The AMS-3946 is currently undergoing testing by several major offshore operators, for potential applications in the North Sea and the Gulf of Mexico.

The new capabilities of the AMS-3946 are largely attributable to product enhancements based on tunneling magneto resistance (TMR) technology that Kaman invested time in. TMR technology enables the sensors to detect ferromagnetic materials through non-magnetic, conductive and non-conductive barriers. The sensors do not require special magnets to work, making them more economical and easier to install. The technology also makes it possible to set up installations that are leak-proof, penetration-free and hermetically sealed.

AMS-3946 sensors offer a standard measuring range of up to 7 mm and deliver a resolution of 1 micron. They come in standard IP-67 rated threaded, flanged and bolthead style configurations, and are AS4320 pressure-port compatible. For OEM integration, the sensors can be tailored to meet semi-custom and custom requirements as shown in Figure 2.

Typical applications include crack and defect detection, shaft alignment and runout, gear tooth condition monitoring, non-contact speed sensing, surface finish thickness inspections and more.

Kaman Precision Products

Kaman Precision Products has over 60 years of experience designing, testing and manufacturing measurement systems for extreme environments and is a leading provider of inductive and capacitive sensors to major organizations across the oil and gas, aerospace, aviation and power industries.

Regardless of the system or industry, end-users can benefit by working closely with sensor manufacturers early in the design phase to ensure they select the proper technology for the application. Selecting a measurement system that is not suited for the environment can result in early failure and unplanned downtime. Conversely, installing a system that is overdesigned for the application will lead to unnecessary spend. Kaman’s extensive line of products, including the extreme environment series and AMS-3946 series, is uniquely capable of meeting the requirements of operators in demanding industrial applications.

To find a measurement system that fits your exact needs, contact Kaman’s engineers today.