Benefits of piezoelectric technology in Weigh In Motion (WIM) systems

Quartz piezoelectric technology: the solution of choice for Weigh In Motion (WIM) systems

Two technologies have become established as the preferred solutions for most all force measurements: quartz piezoelectric sensors, and strain gauges. In some industrial situations, both methods deliver results of comparable quality (the determination of forces acting on a Ø 10 mm milling tool is one example). But there are other applications where practical experience proves that one of the alternatives is clearly superior – and this is definitely true in the case of Weigh In Motion (WIM) technology, where quartz piezoelectric (PE) sensors offer far greater benefits than strain gauges. So, what are the precise reasons for preferring quartz PE technology over strain gauges in a WIM system?

Installation depth

Quartz PE sensors for Weigh In Motion applications are less complex in design than strain gauges, so they are smaller and more compact. This reduces the effort needed to install them under the highway's surface: they can be installed in the road pavement at depths of as little as 55 mm, so the work can usually be completed in one or two days with minimal disruption to traffic. The dimensions of strain gauges, on the other hand, have to be increased in order to lower tensions – and, as the U.S. Department of Transportation notes in its "Weigh-In-Motion Pocket Guide": "The strain gauge strip sensor installation currently recommends 3-inch-deep channels (= 7.6 cm) cut in pavement for installation. This installation requirement limits (the) applicability of (the) strain gauge strip sensor for thin pavements." Kistler also offers a new service – Structural Road Analysis (SRA) – to help customers identify and qualify the most suitable locations for installing their WIM systems: learn more here.

Shallow installation depth of quartz PE sensors in Kistler Weigh In Motion (WIM) system.

Durability and robustness

Quartz piezoelectric sensors have a proven standard life span of over five years. In the USA, where Kistler WIM technology is operated in 43 states, the first quartz PE sensors were installed in 2003 – and the system is still operating with the same sensors today! Lifetimes of ten or more years are not unusual, so there is ample experience to show that quartz PE sensors offer our customers excellent value for money. Quartz PE sensors also feature overload protection: they can withstand overloads of 20% and in some cases, they can even cope with 50% overloading for short periods. By contrast, the yield point/elastic limit of the metals (such as constantan) used in strain gauges cannot be extended to infinity, and this one of several reasons why their fatigue life is limited.

Quartz PE sensors in Kistler Weigh In Motion (WIM) system are durable and robust.

Width of measuring range

Probably the best-known advantage of quartz PE sensor technology is its wide measuring range. In other words, the consistent sensitivity of quartz PE technology means that trucks, cars and even bikes passing the WIM site will have their weight measured and recorded with equal accuracy. Many piezoelectric materials feature a high modulus of elasticity ; quartz PE sensing elements show almost zero deflection, and the sensors benefit from extremely high natural frequency and excellent linearity over a wide amplitude range. Quartz piezoelectric technology is also insensitive to electromagnetic fields and radiation. Strain gauges can only achieve comparable measuring ranges and performance if a much more complicated design is implemented – so load cells of this type are heavy and difficult to handle. And although strain gauges perform well at the maximum end of the weight scale, their efficiency decreases sharply for lighter vehicles. See: Lineas sensor data sheet

Quartz PE technology in Kistler Weigh In Motion (WIM) offers a wide measuring range.

Fully controlled production process

As a leading provider of quartz piezoelectric (PE) measurement technology, we are in full control of the entire manufacturing process at our Swiss headquarters. Disk-shaped crystals, the same size as a contact lens, are installed over the whole length of the sensor – and Kistler even operates its own facility for growing crystals according to a proprietary formula. Cutting-edge production equipment operated by highly qualified specialists ensures that potential fault sources are excluded at the earliest possible stage; in-depth final inspections include a tightness check and various function tests; uniform sensitivity throughout the sensor’s entire length is verified on the calibration system. Over 50,000 Lineas sensors for Weigh In Motion (WIM) have already been manufactured in-house and shipped from our plant in Winterthur, Switzerland. Systems based on Lineas sensors have regularly set global benchmarks for accuracy, reliability, lifetime, and ease of use. Learn more about our sensor production.

Kistler Weigh In Motion (WIM) systems based on quartz PE technology are made in Switzerland.

Global support and service

Kistler offers a portfolio of added-value services to enhance the usage and lifetime of quartz PE-based WIM systems. Our aim: a carefree user experience throughout the lifetime of every WIM installation. We provide assistance to determine the best location for the system installation, as well as training and certification so customers' own staff can execute high-quality installations. Our services also include calibration and optimization to ensure maximum accuracy, and warranty extensions of up to five years for added security. Quartz PE installations in over 50 countries on all continents prove that we can provide local support for system integrators authorized by governments or road operators. With a presence in over 60 countries, Kistler is excellently positioned to provide on-site installation support and additional services for Weigh In Motion across the globe. Discover our WIM services.

Kistler provides value-added service for its Weigh In Motion (WIM) systems worldwide.
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