What are high temperature accelerometers and how do they work?

Today, we rely on mobile mapping systems in our smartphones and cars to get us to our destination as quickly and accurately as possible. While global positioning signals (GPS) pinpoint your exact location, the app you’re using is constantly searching for data from navigation aids to tell you how far you are from your destination, how quickly you’ll get there and where your car is pointed. This is where the small accelerometer in your mobile phone or car comes into play.

The accelerometer enables Maps to predict the time needed to reach your destination. It does that by measuring the phone’s or car’s rate of acceleration, which is the speed your device or vehicle is moving in a certain direction. From that point on, Maps can predict your trajectory, provide the fastest route and a time estimate for your arrival. 

This is one example of what a simple accelerometer can do. If you scale the requirements of your smartphone against the requirements of a complex machine, like an airplane, spaceship or an oil rig, that operates in challenging environments, you will get an idea of what high temperature accelerometers are about and what they are needed for.

What are accelerometers?

Accelerometers are tools used to measure proper acceleration, which is the rate of velocity change of a body in its own instantaneous rest frame (the frame of reference in which the body is at rest). Proper acceleration is different from coordinate acceleration - where acceleration occurs in a fixed coordinate system - and is essentially the acceleration felt by objects and people, also known as g-force.   

Accelerometers typically consist of a proof mass or test mass situated on a spring. When acceleration is experienced, the proof mass reacts by moving to the point where the spring can then accelerate the mass at the same speed as the casing. The spring’s level of compression is what provides the measurement for the acceleration.

How many types of accelerometers are there?

Accelerometers are defined by vibration sensors that divide them in three types: piezoelectric, piezoresistance and capacitive.

Piezoelectric accelerometers are highly sensitive tools that use the piezoelectric effect to monitor changes in acceleration. The piezoelectric effect refers to materials releasing electricity under physical stress. Because of their increased sensitivity, piezoelectric accelerometers are mostly used in shock and vibration measurement.

Piezoresistance accelerometers are more robust and utilize increased resistance based on the amount of pressure that is applied to them. This type of accelerometers is commonly used in crash testing operations.

Capacitive accelerometers measure an object’s acceleration based on changes in electrical capacitance and are the most widely used type of accelerometers, including high temperature accelerometers. They are extremely reliable and precise.

What are accelerometers used for?

Accelerometers are employed in many industries and have multiple uses. For instance, in aviation, accelerometers provide information about the vertical load of the airplane. They are also integrated in inertial navigation systems that are used on spacecraft, aircraft, missiles and ships.

Small-sized accelerometers can be found in digital cameras, tablets, smartphones and even drones, where they ensure that images are always displayed in the right direction and, in the case of drones, help stabilize flight.

Another purpose of accelerometers is free fall detection. This is an interesting characteristic of how accelerometers are designed to work. Accelerometers provide data for tridimensional objects, so they measure acceleration in all three dimensions. An accelerometer resting on a flat surface will not provide 0 results but will measure acceleration based on Earth’s gravity – that’s one direction and what the accelerometer actually measures is the force of gravity. However, if the object is in free fall, the accelerometer will measure 0 in all three dimensions. This is the only instance an accelerometer will provide such a result, which will suggest an object is falling out of control.

When more accelerometers are coordinated together in a system, like an inertial navigation unit, they are able to provide data on proper acceleration, such as direction and magnitude, which is useful for orientation and position.

High temperature accelerometers have all these properties but are specifically designed for demanding environments and industries, like energy exploration, and come with special technology that protects the sensors from heat damage.

What are high temperature accelerometers?

High temperature accelerometers are designed to be hard-wearing in order to provide accurate information in challenging industries, like aerospace and oil & gas. In short, the purpose of a high temperature accelerometer is to be able to do its job while in unfriendly environments, like underground, at very high or very low temperatures and so on.

Companies that manufacture high temperature accelerometers use specific technologies to secure the integrity of the sensors contained by an accelerometer in extreme conditions.

For example, Honeywell’s Q-Flex accelerometers employ the Q-Flex design, an industry standard when it comes to high temperature accelerometers. This model of high temperature accelerometers uses an amorphous quartz proof-mass structure that reacts when acceleration occurs in what is called a flexure motion. This system delivers excellent bias, scale factor and axis alignment stability.

There are also high temp accelerometers that use external amplifiers to protect the amplifier containing the sensor from heat damage.

How are high temperature accelerometers used?

High temp accelerometers are essential for high temperature instrumentation because they are ruggedized and can face extreme conditions, like continuously high temperatures, shock and powerful vibrations. This is why they are frequently demanded in the oil & gas industry, where they are used in a process called measurement while drilling (MWD). This is a well logging method that uses measurement tools within the drillstring to provide real-time data while the drill is steered. High temperature accelerometers can be used with other sensors, like gyroscopes for angular velocity and magnetometers, to provide precise measurements on hole drilling, which is particularly useful in energy exploration sites. 

Furthermore, they are a crucial addition to this type of robust environments because the data provided can help reduce downtime and prevent operational failures, that can cost lives.

Honeywell has a long-standing heritage in high temperature accelerometers manufacturing. The Q-Flex product lines offers a complete range of solutions for energy exploration and other demanding industrial environments, where reliability and accuracy are key.

Specifically, the QAT range and the Mini Q accelerometers are designed to meet the demands of oil & gas applications and are able to operate without fault at extremely high temperatures. Honeywell’s high temperature accelerometers are featured with analog output, square or round mounting flange options, field-adjustable range, internal temperature sensors for thermal compensation and more.