Temperature Measurement in the Hyperloop

Telsa’s CEO Elon Musk has a vision – traveling from A to B at record pace in the Hyperloop. He is pushing the development of this pioneering transportation technology. High-speed transportation needs precision sensor technology to take over important monitoring tasks. The surface temperature of drive wheels, battery voltage, current, engine temperature, engine speed, acceleration, ambient pressure and pressure in pneumatic systems can all be checked by compact infrared temperature sensors from Micro Epsilon.

Ultra-compact infrared temperature sensors from Micro-Epsilon for real-time temperature inspection of the drive wheels in the Hyperloop.

The Hyperloop bears a resemblance to the principle of a pneumatic dispatch system. Electrically driven transport capsules are conveyed on air cushions using solar energy via a tube in partial vacuum. This idea isn’t a new one: George Medhurst already thought of this principle in 1812. Stakeholder of the online payment provider PayPal, Elon Musk, who is also known for his success with Tesla e-cars and the private aerospace company SpaceX, has been pursuing his idea of fast locomotion.

Musk claims that the Hyperloop allows travel speeds up to 1500km – substantially quicker and cheaper than by train. In June 2015, the SpaceX Hyperloop Pod Competition was organized with the aim of speeding up the development of Hyperloop.

Students at the Technical University of Munich took part in this first international competition. Teams had to design transport capsules also referred to as ‘pods’. More than 700 teams applied for the competition and only 30 were invited in January 2017 to test their capsules in the 1.2km-long pipe in California.

After they had passed numerous functional tests, the WARR Hyperloop Team of the Technical University of Munich was chosen out of three teams to send its capsule through the tube. Visionary Elon Musk witnessed the capsule’s travel in person.

Only the capsule that got to the finish was that designed by the Munich students. It won the main prize for the fastest Hyperloop pod developed by more than 32 students. In summer 2017, the students then won the second Hyperloop contest in Los Angeles. They achieved top speeds of 324km/h, which is more than 200 miles per hour.

The high speed transportation capsule is, among other things, equipped with thermoMETER CSmicro miniature infrared temperature sensors from Micro-Epsilon. Their job is to monitor the surface temperature of the polyurethane-coated drive

wheel and ten coated running wheels. The drive wheel has a radius of 80mm and achieves maximum rotational speeds of 12,000rpm. The running wheels have a radius of 25mm and keep the vehicle on the rail. The surface temperature has to be checked during the capsule’s travel and also in the internal test bench to ensure durability of the wheels and to control their wear.

The temperature of the polyurethane coating of the wheels should not surpass 120°C. Knowing these values also allows the evaluation of limits and permanent load in order to make improvements if necessary.

The capsules (or pods) are sent through the 1.2km-long SpaceX testing tube installed in California.

In order to exactly determine the surface temperature of the wheels, the thermoMETER CSmicro temperature sensor is installed approx. 75mm above the surface of the drive wheel surface.

A circular, high resolution measurement spot with a diameter of 7mm is positioned at the center of the wheel, which allows the precise determination of the temperature.

The challenge of this measurement task is the high rotational speeds under difficult thermal conditions in a vacuum. This high rotational speed makes contact measurements impossible. Therefore, non-contact sensors need to be used that resist harsh vacuum conditions and that offer precise, reliable measurements.

As a vacuum does not allow thermal conduction by convection, sensors with a low degree of heat loss have to be be used. This means that the components cannot be cooled using ambient air.

The thermoMETER CSmicro temperature sensor fulfils all requirements of the measurement task. This miniature sensor can be easily installed in restricted installation spaces, due to its compact dimensions. It has a diameter of 14mm, a length of 28mm and is equipped with an M12 fine thread.

The controller is integrated in the cable. Additionally, the sensor loses only a little heat due to its low power consumption of 9mA. Consequently, barely any heat emanates into the vacuum. Due to a detachable sensor head, sensor and controller can be in different places so that the controller is not exposed to the hot environment surrounding the target.

The sensor can easily be used in ambient temperatures up to 120°C without cooling, while the measuring range extends from -40°C to +1,030 °C. The silicon-coated lens is extremely robust. The sensor comes with a scalable analog output and a simultaneous alarm output providing analog and digital connections.

Digital programming for other applications is possible. Martin Riedl, a member of the WARR Hyperloop Team at the Technical University of Munich, is very satisfied with the sensor solution from Micro-Epsilon.

CSmicro is a compact unit that enables us to measure the precise surface temperature. Analog and digital connections give us great flexibility.

Martin Riedl, The WARR Hyperloop Team, The Technical University of Munich

The thermoMETER CSmicro temperature sensor withstands ambient temperatures up to 120°C without cooling, while the measuring range extends from -40°C to +1,030°C. The silicon-coated lens is extremely robust.

The Measuring Principle

Every body with a temperature above absolute zero of -273.15 °C (= 0 Kelvin) emits electromagnetic radiation proportional to its own temperature on the surface which is the so-called "intrinsic radiation" regardless of whether the object is ice or hot steel. Part of this radiation is infrared radiation and can be used for temperature measurements.

This radiation penetrates the atmosphere and is focused by a lens (input optics) in the infrared measurement system onto a detector element, which then generates an electrical signal proportional to the radiation. The signal is then amplified, digitally processed and converted into an output size proportional to the object temperature.

The measured value can be shown on a display or output as an analog signal, which allows easy connection to process control systems.

The three most important factors in IR temperature measurement are emissivity, transmissivity and reflection. The emissivity of a body indicates how much radiation it emits compared with an ideal heat radiator which is a black body.

Optimal temperature measurement is possible at wavelengths where the transmissivity is independent of the thickness, close to zero. However, polyester, polyurethane, Teflon, FEP and polyamide are impermeable at 7.9µm.

Micro-Epsilon is a full-service provider that offers suitable measurement technology for numerous industries. The infrared temperature sensor product range includes both pyrometers and infrared cameras.

These point sensors and infrared cameras can be combined, which enables high standards of quality in exceptional applications but also in common production processes, depending on the application.

IR temperature sensors of the thermoMETER CT series have a modular design and can be used for a wide range of applications in non-contact temperature measurement. From low temperatures prevalent in cooling chains or laboratories, to the highest temperatures in hot molten metals and blast furnaces, these IR sensors measure precisely and consistently.

The temperature sensors can be integrated in applications where installation space is restricted, due to their compact design, for example, in machine building, manufacturing of extremely small devices or OEM applications with multiple infrared measuring positions.

Key features of the thermoMETER product group include fast response times, high resolution and high precision. Particularly with temperature-critical applications, IR sensors from Micro-Epsilon are the preferred choice for small or live objects on the move.

Accurate results can also be achieved with chemicals, in a vacuum or other closed environments. For example, they measure gaskets in a vacuum pump, silicon wafers in a vacuum during processing, plasma coating in a vacuum, in low-pressure plasma for the production of glasses and lenses, in automotive headlight and mirror production and in tool manufacturing for hardened surfaces.

There are many benefits of non-contact temperature measurement, which include: difficult-to-access and very hot objects on the move are not a problem; high speed response times, reactionless measurements, no influence on the target and wear-free techniques.

This information has been sourced, reviewed and adapted from materials provided by Micro Epsilon.

For more information on this source, please visit Micro Epsilon.

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