Why does a Light Weight Deflectometer need to be calibrated?

The Light Weight Deflectometer (LWD) for the dynamic load plate test according ASTM E2835-11 is a globally recognized measuring device for the dynamic plate load test. This compact and mobile testing system allows the bearing capacity of soils to be determined quickly and reliably in earthworks, road construction, civil engineering, pipeline construction, and landscaping.

In order to be used for official compaction and bearing capacity verification, the device must be calibrated annually at a calibration laboratory approved by the German Federal Highway Research Institute (BASt). Calibration must be carried out in accordance with the valid calibration regulation TP BF-StB Part B 8.4.

Only devices with a valid calibration certificate may be used as an official test method on construction sites. Measurement results from devices with expired or invalid calibration must not be used to assess soil bearing capacity.

“Most of our customers have their devices calibrated during the winter months from December to March,” says Frank G. Schulz, CEO of TERRATEST GmbH.
“We are very well prepared for this seasonal peak in order to keep downtime on construction sites as short as possible. During the winter months, TERRATEST operates with a vacation freeze, and the first VIP calibrations already start between Christmas and New Year, so that many customers can use their devices again from the second calendar week of the new year. We even receive devices from Australia or Peru for calibration — of course, we also handle the complete air-freight logistics for our customers. Every device is thoroughly checked and automatically updated with the latest firmware and newest functions.”

TERRATEST is the only company worldwide operating five BASt-approved in-house calibration rigs for Light Weight and Medium Weight Deflectometers. These calibration rigs were developed and built by TERRATEST itself.

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How does the calibration process work?

1. Mechanical and electronic functional check

After arrival at TERRATEST, each device is first tested for proper mechanical function. Then the electronics department checks all electronic components, including:

• sensor
• cable connections
• printer
• high-performance rechargeable battery

In addition, the latest firmware is installed automatically. The rechargeable power battery has a typical service life of at least four years. During calibration, its remaining capacity is checked to ensure reliable operation on construction sites.

If any components are defective or worn, repairs are carried out only after customer approval, based on a detailed cost estimate.

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2. Force calibration of the loading device

After the technical inspection, the actual calibration is performed in the calibration department.

First, the impact force of the loading device (rod with falling weight) is adjusted to 7,070 N. This is done by adjusting the drop height via the release mechanism.
The setting is then verified by 30 consecutive drops. The permissible deviation of the impact force within this series must be no more than ±1%.

For Medium Weight Deflectometers with double impact force, the force is set to 14,140 N. According to test regulation TP-Gestein 8.2.1, these devices can also be used to test heavy crushed-stone base layers.

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3. Calibration of the settlement measurement

Next, the settlement measurement of the sensor is calibrated. This is carried out using three rubber pads of different thicknesses, simulating hard, medium, and soft soil conditions.

During loading, three high-precision displacement transducers measure the actual settlement of the load plate. These reference values are compared with the readings from the TERRATEST sensor.

The calibration of the Light weight Deflectometer is only considered successful if the deviation between reference measurement and sensor reading is less than 20 µm (micrometers).
For each rubber pad, ten consecutive drops are evaluated. For comparison: a human hair has a diameter of about 30 µm.

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Precision for reliable construction site results

The entire calibration process is a technically demanding and precisely defined procedure. It ensures that every Light Weight Deflectometer for the dynamic load plate test delivers highly accurate and reproducible measurement results on site — an essential requirement for safe construction decisions and standards-compliant documentation.

Light Weight Deflectometer – MILANO Transport Box Now Even More Compact

A Light Weight Deflectometer (LWD) is one of the most important testing devices in modern construction. Whether in road construction, civil engineering, pipeline construction or landscaping – wherever soil compaction quality needs to be reliably verified, the Light Weight Deflectometer is the tool of choice. It provides fast, precise and standard-compliant measurements in accordance with TP BF StB Part B8.3 and has become an international benchmark.

To ensure that a Light Weight Deflectometer can be used reliably for many years, safe transport and proper storage are essential. For this purpose, TERRATEST® developed the MILANO transport box, which has been successfully used by customers worldwide for many years.

Why a Light Weight Deflectometer Is Indispensable

A Light Weight Deflectometer provides exact information on soil bearing capacity and compaction. Site managers, engineers and testing companies use it daily to ensure that construction projects are built on a solid foundation. Thanks to its mobility, ease of use and high accuracy, the device has become an indispensable companion on construction sites.

Safe Storage with the MILANO Transport Box

The Light Weight Deflectometer is a high-precision measuring device and must be protected accordingly. The MILANO transport box fulfills this role perfectly:

• Exterior made of robust flight case material
• Interior lined with handcrafted plywood panels
• Custom designed for the Light Weight Deflectometer

This prevents the device from moving loosely in the vehicle and helps ensure a service life of at least 15 years.

The Third Generation of the MILANO Box

More Compact Design for Greater Convenience

The third-generation MILANO transport box is even more space-saving:

• 60 mm narrower
• 30 mm lower
• 3 kg lighter

This was achieved by storing the load plate at an angle inside the box. This clever design not only saves space but also improves ergonomic handling. Removing the load plate is now more convenient, and the entire unit fits more easily into the trunk.

Backward Compatibility and Safety

Another important advantage: the box is backward compatible. Even older LWD models (as far back as 2012) can be transported safely. Additional fixings further enhance stability. Even a drop from one meter can be withstood without damaging either the box or the device – a strong argument for maximum safety.

Since 2008, TERRATEST® has delivered more than 10,000 MILANO boxes worldwide. Around 80% of all Light Weight Deflectometers are sold together with this transport box.

Practical Features for Everyday Construction Use

Standard Wheels for Daily Transport

The MILANO comes standard with integrated wheels, making it easy to pull the Light Weight Deflectometer across parking lots or slide it into the trunk.

Off-Road Wheels for Construction Sites

For tough construction site conditions, TERRATEST® also offers the box with off-road wheels. This allows the approx. 50 kg device including box to be moved across sand, gravel or uneven ground – a major benefit for users who need maximum mobility on-site.

Conclusion – The Perfect Companion for Every Light Weight Deflectometer

With the third generation of the MILANO, TERRATEST® once again demonstrates its customer focus. The Light Weight Deflectometer is not only safely protected in the new box but also transported more compactly, more lightly and more ergonomically.

Anyone using a Light Weight Deflectometer benefits from the MILANO transport box:

• Greater convenience through a more compact design
• Enhanced safety thanks to robust construction
• Increased flexibility with optional off-road wheels

The new MILANO is therefore the ideal companion for anyone who wants to transport their Light Weight Deflectometer reliably and comfortably.

Light Weight Deflectometer at BAUMA 2025

In just a few weeks, BAUMA 2025 will open its doors once again, setting global standards for construction machinery, building material machines, construction vehicles, and construction equipment. From April 7 to 13, more than 3,500 exhibitors from 57 countries will showcase their latest machines, technologies, and innovations across an impressive exhibition area of 614,000 square meters. The trade fair welcomes international visitors from over 200 countries, representing industries such as earthworks, road construction, civil engineering, and landscaping. BAUMA is not only one of the largest trade fairs in the world but also one of the most innovative platforms for knowledge exchange and networking within the construction industry.

TERRATEST® is dedicating its exhibition presence entirely to intelligent and user-friendly Light Weight Deflectometers for dynamic plate load testing. Our goal: to help customers conduct compaction tests even more efficiently and economically. In times of increasing quality assurance requirements in the construction industry, precise and easy-to-use testing devices are more important than ever. Therefore, trade visitors can look forward to numerous innovative features that further simplify the handling of the devices and facilitate daily work.

One of the highlights of this year's presentation is the latest developments in the field of Light Weight Deflectometers. These models now feature integrated Wi-Fi, voice navigation, a modern USB-C charging system, and an even more precise GPS system. These technical innovations enable even simpler and faster measurement data acquisition and transmission. The integrated Wi-Fi, for example, allows wired devices to be seamlessly connected to the TERRATEST app for online data transfer. In addition, the performance of the microprocessor-controlled measurement electronics has been improved, ensuring even more reliable measurements.

Another significant product that TERRATEST® will introduce at BAUMA 2025 is the "TRENCH" Light Weight Deflectometer. This device has been specifically developed for use in narrow trenches, such as those commonly found in fiber optic network expansion. With a load plate width of only 10 cm, it enables precise compaction tests even in hard-to-reach areas. This presents a major advantage for companies operating in the telecommunications sector that require efficient quality control of earthworks.

A special highlight this year is TERRATEST®'s double presence at the trade fair. For the first time, the company will be represented with two exhibition booths: in Hall B5, Booth 116 for construction equipment, and in Hall A2, Booth 138 for testing devices. "We are especially looking forward to BAUMA 2025. For the first time, we will be present with two exhibition booths – both in our established Hall B5 for construction equipment and in Hall A2 for testing devices," says Frank Georg Schulz, CEO and Founder of TERRATEST®. "We are hoping for many visitors and are excited about engaging discussions on load-bearing capacity measurement with the Light Weight Deflectometer."

In addition to showcasing innovative technologies, TERRATEST®'s exhibition booths will feature numerous live demonstrations and opportunities for direct exchange with our experts. Visitors will have the chance to gain first-hand insights into the latest developments and practical applications of the devices. Take this opportunity to meet our competent team in person and experience the advantages of the new device generation. We look forward to welcoming you at BAUMA 2025!

At the BAUMA trade fair, the company will also present the TERRATEST 9000 LWD. This Light Weight Deflectometer is equipped with a geophone and a load cell, and thus complies with ASTM E 2583-07.

Light Weight Deflectometer at GaLaBau 2024

GaLaBau in Nuremberg is the leading trade fair for the garden and landscaping industry in the German-speaking region. In 2022, it attracted more than 60,000 visitors and over 1,000 exhibitors from 32 countries, making it the most significant industry event in Europe. The professional visitors are characterized by their high decision-making competence and come not only from gardening and landscaping but also from related fields such as road construction, earthworks, civil engineering, and pipeline construction.

This year, TERRATEST® will participate in the biennial GaLaBau in Nuremberg for the seventh time and proudly present its Light Weight Deflectometer.

TERRATEST® at GaLaBau 2024

TERRATEST® will once again be prominently represented in Hall 7 at GaLaBau, which takes place from September 11 to 14, 2024, in Nuremberg. A special surprise is the return of Falko Weiss, who has been reactivated from retirement specifically for the fair. "After more than a year in retirement, I am very excited to finally reconnect with customers and personally demonstrate our Light Weight Deflectometer. I hope to welcome many old acquaintances at the TERRATEST® booth," says Weiss with great anticipation.

GaLaBau 2024 promises to be a highlight of the year for TERRATEST® and its customers. The opportunity to experience the new and improved devices firsthand and to be convinced of their quality and innovative strength is something no professional visitor should miss. TERRATEST® looks forward to presenting its latest developments to a broad audience and deepening exchanges with experts and interested parties.

Light Weight Deflectometer re-calibration now

Light weight deflectometer are measuring very precise and highly reliable test results, therefore they have to be re-calibrated every twelve months according to the international standard ASTM E2583-07 (American Society for Testing and Materials) independent of how often it was used in the last 12 month. Regular calibration will guarantee, that test results are always reliable and precise and that the equipment is working correctly. To do this annual service, owners have to resend the entire equipment to the manufacturer, because remote or online calibration is not possible. Winter time is perfect to do this required re-calibration because bad weather conditions are making the use of LWD nearly impossible during this period in most countries of the world. The lead time of calibration service depends mostly on the transport time, which is needed for shipment of the equipment to and from manufacturer and back to customer. Inside European Community it needs three weeks including transport time, calibration for overseas customers needs about four weeks depending on customs clearance. Sending back the equipment from overseas best to use a custom procedure to send equipment as temporary import to avoid custom fee. Proforma invoice issued by users has to be less than 1000 USD for temporary import. This makes custom clearance easier. As soon as the equipment has arrived in Germany, manufacturer will start the calibration process immediately .

The manufacturer is doing re-calibration of light weight deflectometer using three in house designed calibration systems, all accredited by BASt Germany (Bundesanstalt für Strassenwesen, a department of ministry of traffic of the German government), which guarantees that customers do not have to wait a long time for calibration service. The third calibration system was just accepted by BASt in the middle of February 2022. Calibration service means the calibration of the central geophone which calculates the deflection of the soil as well as the calibration of the two external geophones (if part of the equipment) and the calibration of the load cell which is measuring the load of the falling weight. The device works with a 10 kg falling weight and even with 15 kg and 20 kg if the user has purchased these options. Calibration service is according to the international standard ASTM E2583-07 and the manufacturer is following the strict rules of the German calibration standard TP BF-StB 8.4 in addition to make sure, that light weight deflectometer made in Germany will be very precise and reliable when doing compaction tests of soil in the field. After a successfully calibration, a label with the period of the valid calibration year will be attached on the equipment.

The service includes the check up of all functions of the device as well to make sure that the light weight deflectometer will work bug free at least till the next re-calibration after twelve more months. If dust or sand is in the device, the parts will be disassembled and cleaned carefully by technical staff. Before a necessary repair, the manufacturer will ask the owner to approve a commercial offer send via email where all repairs are explained and listed.

The manufacturer reminds all customers every year via email with a special calibration reminder service, that the calibration period of their equipment is expired.

Light Weight Deflectometer (Part 1)

Light Weight Deflectometer (LWD) with Geophone

Light Weight Deflectometer is not like Light Weight Deflectometer. Watch out for the differences between two types of eqipment. It is a non destructive test (NDT) equipment for dynamic load testing of load bearing capacity. Light Weight Deflectometers are offering the most economic way to do non destruction test (NDT) of compaction quality of unbound or partially bound material in earthworks, road constructions, canal construction, railway constructions and utility trenches, all as one single solution. The one person test procedure is done in less than two minutes and still provides full results. No counterweight (truck or roller) is required and tests can be done in places hard to enter. The equipment has no radioactive sources and all tests can be done by one single person.

There are two different types of Light Weight Deflectomete in existence: One type is operating via a Geophone and one type is operating via an acceleration meter. TERRATEST® is the only manufacturer in the world producing both types. And there are many more differences of facilities between these two types of test instruments. The acceleration meter Light Weight Deflectometer (german dynamic load plate test) was invented in Germany several decades before. It meets the german specification TP BF-StB Part B8.3, the ASTM E2835-11, the Austrian specification RVS 08.03.04, the Spanish specification UNE 103807-2:2008, the cChinese specification TB 10102-2010, J338-2004 (standard for soil testing in railway construction), the Czech specification CSN 736192-1996 and the RIL 836 for track laying of Deutsche Bahn (German railway). The geophone type meets the ASTM E2883-07, UK standard IAN 73 and Italian standard UNI 11531-1.

Terratest as the leading manufacturer of Light Weight Deflectometer is asked frequently by customers from all over the world, which type is the best for which requirements. An answer is not as easy as it seems.

First of all customers have to follow the required specification of their specific project in their country. According to the required specification they have to choose the corresponding type. If no specification is required, the type should be chosen according the operation area.

The accelaration model is far easier to use. But it gives the user even less features than the geophone one. Following the instruction manual, one single person can handle the gauge immediately, no training is necessary. The test procedure does not require a counterweight like a truck or roller and the test procedure needs less than two minutes. Immediately after the test procedure users can printout a test protocol and will have the result in their own hands. In Germany results can be used according to the specifications ZTVA and ZTVE as an official compaction proof.

Thanks to the short time needed for each single test the compaction quality of all layers can be tested all over the construction site, even on natural ground before starting the earthworks.

It provides an immediate method to the workers in the construction site before, during and after the compaction process to determine the load bearing capacity of unbound soil to make a statement about the compaction quality. Moreover the compaction process can be managed directly at any stage of the procedure The Light Weight Deflectometer is used for self monitoring and even to provide official proofs.

Light Weight Deflectometer for Safe Foundation

The construction boom in Germany is continuously growing. Comfortable prefabricated houses and solid buildings are in progress all around. The bearing capacity of the soil is an imperative condition to be evaluated beforehand - particularly below the foundation plate, as this element represents the interface between house and subsoil. It is the purpose of the foundation plate to distribute the weight of the building in a homogeneous manner and to protect the building from heat/cold and vibrations of the ground. The available ground however is often not strong enough to carry the foundation plate without additional earthwork. Therefore besides deep sounding, analysis of the bearing capacity of the grown soil is required. A light weight deflectometer is an adequate instrument, since it is able to perform a measurement within only two minutes. The simple service as well contributes to a quick establishment of comprehensive measurement sequences. This way, a qualified assessment concerning the entire field is possible in no time. In the case of cohesive soil or inclination of the site, soil replacement has to be carried out. Sometimes several meters can be involved. For these works, it is important that the new soil is inserted by layers and that these layers are individually compacted by vibratory plate. Thickness of each layer should not exceed 30 cm, and evidence of qualified compaction must be provided each time. For this inspection, a light weight deflectometer is an ideal instrument. Minimum requirement for the bearing capacity of soil for private homes usually amounts to 30-40 MN/m² for the layer directly below the foundation plate.

„During each construction project, we carefully examine the quality of the earthwork for cellars and foundation plates. Compaction work and subsequent compaction control is of major importance. Particularly in places with difficult access, there is no alternative to light weight deflectometers. They do not need a counterweight, and the assessment is easy to perform “, declares project manager Kai Wolts. Mr. Wolts and his company recently invested in 14 light weight deflectometers produced by TERRATEST from Berlin. From now on, each construction gang disposes of its own measuring equipment and can immediately provide itself evidence for the compaction of the soil. „This fact ensures our independence from external geotechnical experts, thus saving time and money.”

All around Germany, light weight deflectometers make themselves indispensable, as settlement damages turned out to be a serious topic for several companies, causing major follow-up costs. Particularly for foundation plates, insufficient compaction of the subsoil gives rise to exorbitant expenses, as the whole building may be subjected to cracks. Therefore before pouring the foundation plates, measurement of the bearing capacity of the subsoil is imperative. „Since many years, we trust in light weight deflectometers, and are continuously in action in the vicinity of Berlin with three of them”, emphasizes construction engineer Norbert Wenzel from Frankfurt (Oder). „Besides prescribed core sounding, we are carrying out also measurements by means of light weight deflectometers, to ensure homogeneous bearing capacity and sufficient compaction quality of the soil, before pouring the foundation plate. This is an essential element of responsible construction management”, so his opinion.

The essential benefits of light weight deflectometers are obvious: 

• Measurements can be carried out by each capable member of the team in no time.
• Large measurement sequences are possible even under tight deadlines, as each measurement takes only two minutes.
• Counterweights like road rollers are not necessary.
• Compaction work for each layer can be accompanied by measurements.
• Homogeneity of bearing capacity can be checked already during insertion of the layers.