Optimizing weighing technology

Optimising weighing technology

Strain gauge technology is helping to improve the accuracy and stability of both static weighing and WIM applications, while also providing a low cost of ownership and a certifiable performance

Words | Jon Arnold, transportation market manager, Intercomp Company, USA

There are various scales and sensors that can be employed to acquire vehicle weights. Each measurement technology has its benefits. For USA-based manufacturer Intercomp, the design and manufacture of products based on strain gauge technology has been its focus for over 40 years. With a portfolio that includes certified portable static, and certified portable and in-ground weigh-in-motion (WIM) scales and sensors, the benefits of strain gauge technology are available across a large range of weighing applications.

Strain gauges at work

Weighing vehicles on static truck scales relies on strain gauge load sensing. This method is widely used in weighing for legal and direct enforcement applications and is viewed as the most accurate means to weigh a vehicle. Strain gauge sensing possesses inherent performance characteristics, which include accurate performance, linearity throughout the capacity range, and internal temperature compensated output. These characteristics ensure repeatability and stability over time and across changes in temperature. This assists in the certification of scales and systems to metrological and performance standards throughout the world.

The well-known performance of strain gauge load cells has led to its use within force and weight measurement for many decades, as well as widespread incorporation into scale manufacturing and field use. Low acquisition cost and an absence of moving parts allows for fully electronic scales and sensors to be constructed that provide accurate performance while avoiding unnecessary maintenance.

Above: Strain gauge scales and sensors for vehicle weights

WIM sensors

Designed for use at speeds starting at 2mph (3km/h) ranging up to mainline speeds, Intercomp WIM strip sensors provide OIML R134 certified performance for low, medium, and high-speed weighing applications. In addition to achieving certification for high-speed WIM direct enforcement in several countries, uses also include data collection, screening for enforcement, tolling, and border or industrial check weighing applications.

Installed in pairs in the pavement across the traffic lane, the WIM strip sensors measure axle and gross vehicle weight (GVW) in addition to axle spacing and vehicle length. Typical installations include between two to eight sensors in multiple rows, depending on the required accuracy, and are available for integration to a variety of different electronics and software. To secure the sensors in place, small channels are cut into the pavement. There is no need for drains. The minimal sensor depth and form factor enable rapid installation.

Strain gauge technology provides a stable and temperature compensated output for the integrator’s electronics to measure vehicle data. As temperatures fluctuate over the course of seasons or even throughout a single day, end

users can be confident that a strain gauge WIM system will stay within performance tolerances.

Portable weighing

80mph

The speed up to which Intercomp’s WIM sensors can accurately weigh vehicles (130 km/h)

Strain gauge technology has a history of use within static weighing. Intercomp has developed portable scales that operate in static mode, or have both static and WIM capabilities. Several of these scales are certified to National Type Evaluation Program (NTEP) and OIML R76 static performance requirements.

The benefits of low-profile strain gauge technology can be seen in the in the NTEP and OIML R76 certified LP788 wheel load scale. As the first scale in the Intercomp 788 series of portable scales, the design is highly portable at 17kg, with a scale platform height of only 0.85in (22mm). Typically deployed in sets of two or more scales for weighing wherever vehicle weighing is required, the scales use solar charging, and wirelessly communicate with indicators and software. The low profile makes it easier and safer for vehicles to climb onto the scales. Variations of the design are used for in-motion applications as well as vehicle inspections and tyre ratings of individual tyres within a dual-wheel configuration.

Intercomp has strain gaugebased scale and sensor options for in-ground and portable WIM and static scales and sensors, depending on the weighing requirements. Building on existing NTEP and OIML scale certifications, the company offers a wide range of performance tested and approved products to acquire vehicle and weight information. ■

Above: Low profile portable scales certified for enforcement

A BETTER WEIGH

OIML Certified Scales & Sensors

LP788™ Portable Scale LS-WIM® Weigh-In-MotionAxle Scale

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