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Piezo Accelerometers

If you’re looking to build a piezoelectric accelerometer that suits your specific needs and specifications, precision-manufactured piezoelectric accelerometer components can help. Choose from standard piezoelectric sensor component options, as well as customized solutions based on your specific needs.

No matter if you need to produce large volumes of customized piezo sensors, customized experimental devices in small quantities, or sensors for university and private research, it’s important to start with the right types of quality components.

Principles of Operation

An accelerometer is a type of sensor that measures force due to acceleration of the sensor. For illustrative purposes, imagine a wooden box with wheels and a concrete block inside. Now, imagine that somebody gives that box a generous push. If that person pushes and accelerates the box quickly enough, the concrete block inside the box might slide. This is because both the box and the concrete block have inertia and resist changes in their movement accordingly.

As the box accelerates, the inside surface exerts a shear force against the surface of the concrete block thereby causing the block to move with the box — unless the shear force exceeds the maximum force allowable due to friction. However, if that block was firmly cemented to the inside surface of the box, the block would never slide regardless of the rate of acceleration.

Now, suppose that the cement between the block and the inside surface of the box is replaced with a shear mode piezoelectric plate to sense the shear force. The corresponding wires are attached from the piezo plate to a multimeter. In this case, if you decide to give the box a good shove, you might notice a change in the voltage reading. This change in voltage reading corresponds to the shear force between the block and the box.

Metaphors aside, what you may have been imagining is a crude and simple piezo accelerometer. The basic operating principle of any accelerometer is that a mass of known quantity is suspended and constrained by a calibrated force-sensing transducer. That way, the transducer can measure all force exerted on the mass due to acceleration. In the case of a piezo accelerometer, the force is measured using an integrated piezo sensor.

Types of Configurations

Many times, design requirements dictate that an accelerometer be capable of measuring acceleration components in multiple directions. In this case, multiple masses and transducers are embedded into a single compact unit and form a multi-axis accelerometer. For instance, a two-axis piezoelectric accelerometer would include two sets of masses and piezo sensors placed along the desired axes of measurement. They are integrated into a single package. Likewise, a three-axis accelerometer would include three sets of masses and sensors oriented and calibrated appropriately.

Some applications may even require piezoelectric accelerometers to measure rotational acceleration about one or more axes. Do you require a three-axis accelerometer that measures both linear and rotational acceleration components about each of the three axes (a total of six measurements)? At APC International, we have engineers who can advise you regarding the development of such hardware.

Piezoelectric accelerometers may or may not incorporate integrated signal-conditioning circuitry. Simply put, signal-conditioning circuitry receives the raw voltage output from the accelerometer’s piezo sensors. It then converts it into a more convenient signal that’s more readily processed by instrumentation.

Signal conditioning circuitry may include filters, amplifiers, limiters, clampers, or any other combination of analog and digital circuitry necessary to convert the raw accelerometer output to usable formats. Some individuals prefer to use current loops as the output for noise resistance and fault detection — others may prefer voltage outputs with specified output impedances.

Without integral signal conditioning, piezoelectric sensors operate in charge mode. In charge mode, the raw high-impedance voltage output(s) of the accelerometer are fed directly over a cable to the appropriate electronics or instrumentation.

APC Figure 3.4

Piezo Accelerometer Advantages

Piezo accelerometers offer a variety of benefits, including:

Frequency Response — Piezoelectric sensors have a wide frequency response. After all, piezo sensors are used in applications ranging from sensing the low frequencies of a bass guitar to sensing and transmitting the high frequencies of an ultrasonic device. This means the performance of piezoelectric accelerometers over a broad frequency range is unsurpassed by other accelerometer technology currently on the market.

Temperature Stability — Piezoelectric sensors are intrinsically stable over wide temperature ranges. This characteristic enables piezo accelerometers to be used comfortably in applications where competing technologies would quickly fail. Some of our piezo accelerometers can operate at temperatures as high as 160 C (320 F). This allows them to be mounted directly to many types of industrial machinery without the need for cooling.

Ruggedness — Our piezo accelerometers are intrinsically robust. This is due to their solid-state design and our extraordinary manufacturing expertise acquired since our beginning in 1986.

Adaptability — When you tell us about your intended application, our engineers will make every effort to ensure you receive a satisfactory product — a product that meets or exceeds the requirements of your intended application.

Electrical Characteristics — For all practical purposes, our piezoelectric accelerometers output voltages that are linear and proportional to measured rates of acceleration. This greatly simplifies signal conditioning and even allows signal conditioning electronics to be placed a considerable distance away from the accelerometer. We also have the skill and expertise necessary to implement signal conditioning hardware to satisfy unique customer expectations.

Typical Applications

Piezo accelerometers can be used in a variety of settings and environments, and many of our customers have unique applications. APC International’s engineers can help you design a solution that fits your precise requirements. Some common applications include:

Engine Knock Sensors — Engine manufacturers are constantly facing challenges related to the control of engine parameters. Under the wrong circumstances, gasoline engines are susceptible to an undesirable phenomenon known as detonation. When detonation occurs, the air/fuel charge explodes instead of burning smoothly — and this damages the engine.

Historically, most manufacturers designed engines with conservative operational margins at the expense of efficiency to avoid this notorious problem. However, with the development of better control systems, the relevant engine parameters may be adjusted in real time to maximize efficiency and power. If detonation begins to occur, engine knock sensors can sense the detonation before it becomes problematic so control systems can make the required adjustments. Our piezo accelerometers are particularly suited for engine knock sensors given their intrinsic thermal stability and high frequency response.

Vibration Testing and Monitoring — Piezoelectric accelerometers are often employed in vibration analysis of machinery. Under some circumstances, engineers may want to continuously monitor the vibrations of one or more pieces of equipment in an attempt to predict costly failures before they occur. In other cases, a customer may be concerned about minimizing equipment noise. They want to implement monitoring so excessive noise can be detected before becoming problematic.

Shock Pulse Monitoring of Motor Bearings — Shock Pulse Monitoring (SPM) of motor bearings is a relatively recent technique employed for monitoring health and lubrication of bearings. Whenever metal-to-metal contact occurs within a bearing during equipment operation, shock pulses are generated as the metal surfaces collide.

Healthy bearings exhibit relatively few high-amplitude shock pulses amidst a plethora of low amplitude shock pulses. Bearings that are near the ends of their lives or living on “borrowed time” exhibit a large number of high-amplitude shock pulses. This is because metal surfaces are colliding more forcefully and more frequently than they would otherwise be in a healthy bearing.

In a typical SPM installation, a piezo sensor is mounted on or near the bearing housing, and an instrument is connected to monitor the output. Using digital signal processing techniques, the ratio of high-amplitude shock pulses to low-amplitude shock pulses can be monitored and interpreted to indicate bearing health. Under some circumstances, industrial facilities that employ many pieces of rotating equipment may elect to continuously monitor the shock pulses. This allows them to predict failures in advance and avoid costly downtime.

Inertial Navigation — Airplanes, spacecraft, submarines, and various forms of weaponry rely extensively on inertial navigation that enables them to navigate precisely using advanced forms of dead reckoning. The intrinsic ruggedness and thermal stability of our piezoelectric accelerometers will help your machine function satisfactorily in harsh environments with extreme temperatures.

Drones and Unmanned Aerial Vehicles — Autonomous aircraft utilize accelerometers extensively to monitor their stability and position.

Impact Testing — Equipment shock and impact testing necessitates a robust and reliable means of measuring sustained shock. Often, tests of this nature are repeated multiple times and the relevant sensors need to withstand repeated abuse. The wide operational range and durability of our accelerometers make them ideal candidates for these types of applications.

Vehicle Stability Control — Recent changes in automotive safety standards now mandate the addition of vehicle stability control to all passenger vehicles manufactured for sale in the United States. One safety-critical component for any stability control system is an accurate and reliable array of accelerometers.

Seismic Sensors — Seismic sensors require particularly sensitive and rugged accelerometers to be effective, since sensors can be buried beneath the ground in remote locations for years at a time.

Security — Security devices often utilize accelerometers to sense movement, jarring, or impact to objects of interest.

Automation — A wide variety of automation applications require accelerometers for various reasons.

Research and Development — You can use piezoelectric products to gain technical advantages in your field. Contact us to learn how our customers are performing research and development with APC International products.

Getting Started

Our team can work with you to meet your requirements, schedule and budget. If you’d like to discuss your piezo project in greater detail or learn more about our selection of piezo sensors, contact an APC International representative today.