Choosing the Right Non-Nuclear Density Meter for Dredging and Mining: Dollars and Cents or Dollars and Sensors?
Slurry density x slurry velocity x interior pipe diameter is the Holy Trinity for the dredging and mining industries. Knowing the answer to this simple formula is fundamental to business success and economic survival that no business can afford to miscalculate, especially in the dredging industry. As such, having the ability to obtain accurate slurry-flow data in real-time is an essential requirement in order make accurate operational decisions in the present, and informed business decisions for the future.
The dredging and mining density meter market was once the exclusive domain of nuclear (gamma) technology. However, the situation has changed to the point where comparing the relative merits of nuclear versus non-nuclear density meters has almost become a non-argument. High operational and disposal costs, alongside associated “red-tape” and other regulatory factors, have served to make nuclear technology less attractive for both the dredging and mining industries.
While there are a number of options available,[1] it seems clear that there are three main non-nuclear density meter technologies that currently dominate the market: ultrasonic, kinetic, and tomography.
The three technologies can be briefly summarized as follows:
- Ultrasonic – think nuclear density meter that uses soundwaves instead of gamma rays. Density is measured according to the relative difference between soundwaves that are transmitted and received.
- Kinetic – density is measured according to movement of a, specially installed, flexible portion of a slurry pipe (this includes what the Damen trial calls “weighing” or “bending”). “Weighing” or “bending” movement is then translated and transmitted via an electric signal that is processed to be able to render density measurements in real-time.
- Tomography – in this case electrical resistance tomography (ERT), works by measuring the relative electrical conductivity of the water and entrained solids inside a slurry pipe. Sensor-derived measurements are interpreted by software to yield a tomogram – a real-time dynamic cross sectional image of the slurry pipe alongside empirical and Cartesian representations of data.
The three technologies outlined above are all interesting in their own right. However as anyone in the dredging or mining industry knows, technology is one thing; real-world application is another.
Like any product designed for industrial use, a density meter must fulfil a basic set of criteria to constitute a good investment for a dredging or mining company. The Damen study[2] makes the following observations regarding what makes a good density meter:
“From an operator’s perspective, a sensor and its processing instrument needs to have a wide application, must be robust, reliable and accurate, and have a low OpEx” [operating expenses or expenditure].
With this in mind, how can we arrive at a basic set of criteria to compare the relative merits of the three main non-nuclear density meter technologies and also find the right balance between business and technology?
Business Money is a well-established business publication who, as their title suggests, cover the nexus between business and finance. In their article entitled “6 Things That All Industrial Products Need To Have In Order”[3] they outlined and defined six essential criteria that a successful industrial product must possess. Business Money’s six criteria are listed and briefly summarised below:[4]
- Durability – an industrial product’s overall lifespan and its ability to “withstand the wear and tear of their [sic] environment and frequent use.” This is self-evident since dredging and mining operate in the toughest environments.
- Efficiency – “Industrial products should be efficient in their design and operation for optimal performance.” This also relates to potential “energy loss” alongside “product design and how it impacts its energy efficiency.”
- Safety – ensuring the product conforms to relevant safety regulations while not compromising efficiency.
- Quality – while this also relates to durability, a prime concern is for this category is a product’s accuracy and reliability.
- Cost effective – products must “be cost-effective in order to maximise their value for money.” In many ways, this is the aggregate of all six categories and boils down to a question of whether the operational advantages of a product justifies its cost.
- Versatility – adaptability is key. A product “must be adaptable to different conditions” which also applies to factors like installation as well as operation. “Versatility also increases the longevity of a product by allowing it to be updated and upgraded easily.”
It is hard to argue with these criteria from a purely business perspective and boil down to little more than just plain old common sense. As we shall see, choosing the right non-nuclear density meter comes down to so much more than just finding the cheapest price – especially given the dredging and mining industry’s notoriously tough operational conditions where a cheaper option may not be as durable and constitute false economy.
Let us examine the relative merits of ultrasonic, kinetic, and tomography technologies when applied to the dredging and mining industries, based on Business Money’s six criteria aligned to the technical observations from the Damen trial since this is probably the most recent 3rd-party comparison of density meter technology carried out in the dredging industry.
The comparison chart below provides a brief summary of the relative merits of each technology based on Business Money’s criteria. Any statement in double quotation marks is taken directly from the Damen’s own comparison table.
Tomography clearly has the most advantages, based on the six listed criteria and from the results of the Damen trial. Out of the eight technologies tested, the Damen study awarded electrical resistance tomography (ERT) the highest overall score with 5. While ultrasonic and kinetic scored 4 and 3 respectively.[5]
Four years is a long time in technology and electrical resistance tomography (ERT) is no exception; an emergent dredging technology in 2021 has become even better in 2025. Tomography software is able to process sensor data much faster, while the data acquisition unit has a footprint that is now 95% smaller.
Smaller, faster, and now more versatile; tomography’s 3-in-1 integration is one of its most compelling attributes with its ability to measure slurry density, slurry bed height, and slurry velocity all in one system and can be more correctly described as a production meter.
Having such a high degree of technological integration avoids the need for hybrid or ‘Frankenstein’ density/velocity meter concoctions where one brand of density meter is accompanied with a flow meter from a different manufacturer using different technology.
Tomography’s powers of integration offer seamless data acquisition in a fully automated “plug and play” platform with a clear user-friendly interface that can be easily used and understood by a layman.
Unlike other velocity meters, tomography is able to measure slurry velocity as a discrete value. Many flow meters are unable to distinguish between water and entrained solids in a slurry flow: tomography can. This allows for a highly accurate calculation of production output.
Measuring bed height is another advantage that tomography can offer as real-time visualisation reduces the chance of a slurry pipe blockage occurring. Bed height measurement is even more important when combined with a rotational sensor spool-piece, which comes as standard. Both the slurry bed height measurement and spool-piece rotation mean that operational wear and tear can be mitigated and operational life extended by sharing the wear evenly around the 3600 internal diameter of the sensor spool piece.
If it hasn’t become apparent by now, it is surely clear that tomography offers the best value for money through its fully rounded integrated operational capabilities and superior technology. As if it didn’t make good business sense in the present, tomography will make even more sense in the future as product updates and new functionalities will only need to be installed via a software update: not a ‘hardware update’ which obviously means more dredge-time without the down-time.
While all three non-nuclear density meter technologies have their merits, any dredging or mining company looking for a (to quote Business Money’s six criteria) durable, efficient, safe, quality, cost-effective, and versatile non-nuclear density and production meter must surely choose tomography. When it comes down to the optics of OpEx, or a question of dollars and cents, the answer surely lies with dollars and sensors!
[1] Bosman F. et al, “Assessing Non-Nuclear Production Instrumentation; ERT Technology as the New Standard for Dredging”, CEDA Dredging Days, 28/09/2021. Damen Shipyards Group conducted a study of eight different technologies under the same trial conditions on board a hopper dredge.
[2] Bosman F. et al, “Assessing Non-Nuclear Production Instrumentation; ERT Technology as the New Standard for Dredging”.
[3] 05 December 2022.
[4] https://www.business-money.com/announcements/6-things-that-all-industrial-products-need-to-have-in-order/#:~:text=While%20safety%20should%20always%20be,use%20of%20any%20industrial%20product
[5] Bosman F. et al, “Assessing Non-Nuclear Production Instrumentation; ERT Technology as the New Standard for Dredging”.
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