ATEX & IECEx EX Certified Density & Viscosity Sensors for Combustible Dust Applications

Enhancing Safety and Process Control in Combustible Dust Environments with EX Certified Rheonics Density Meters and Viscometers

Combustible dust poses a significant explosion risk across industries such as food processing, chemicals, mining, and metal powders. This application note explores how Rheonics EX ia IIIC Da certified SRD density meters and SRV viscometers enhance both safety and process control in Zone 20, 21, and 22 environments under ATEX and IECEx standards. Learn how intrinsically safe inline monitoring of density and viscosity helps prevent ignition risks while improving operational efficiency and product quality.

Table of Content

1. The Pervasive Challenge of Combustible Dust: Ensuring Safety with Certified Process Monitoring
2. Navigating Hazardous Area Classifications for Combustible Dust: ATEX and IECEx Frameworks
2.1. Defining Dust Zones (ATEX & IECEx)
2.2. Understanding Dust Groups (ATEX/IECEx)
2.3. Equipment Protection Levels (EPLs) for Dust (IECEx) and Categories (ATEX)
2.4. Temperature (T) Class Ratings and Maximum Surface Temperature for Dust
3. Intrinsic Safety (Ex i): A Premier Protection Strategy for Dust-Laden Environments
3.1. Levels of Intrinsic Safety (ia, ib, ic)
3.2. Advantages of Using IS-Certified Equipment in Dusty Hazardous Areas
4. Rheonics SRD & SRV: Intrinsically Safe Density and Viscosity Sensors with Robust Dust Certification
5. Transforming Process Control in Dust Hazard Industries: Applications of Rheonics EX Certified Sensors
6. Reference Table: Rheonics Sensor Suitability in Combustible Dust Applications
7. Installation and Operational Considerations for EX-Certified Sensors
Intrinsic Safety System Requirements
8. Conclusion: Advancing Safety and Operational Excellence in Dusty Environments with Rheonics Certified Sensors
9. Reference
10. Disclaimer

1. The Pervasive Challenge of Combustible Dust: Ensuring Safety with Certified Process Monitoring

The risk of dust explosions is a significant concern in many industries. Fine particulate matter, or dust, from materials like grains, sugar, wood, chemicals, and metals can become a potent fuel source when suspended in the air at the right concentration and exposed to an ignition source. For a dust explosion to occur, five conditions must be present: fuel (combustible dust), oxygen, confinement (in a vessel or building), dispersion (a dust cloud), and an ignition source. A dust explosion can lead to rapid pressure increases, catastrophic facility damage, and severe risks to personnel. As a result, using certified equipment that eliminates or controls potential ignition sources is a key part of industrial safety.

In this context, the accurate, real-time monitoring of process parameters such as density and viscosity plays a crucial role. These parameters are fundamental indicators of a material’s consistency, concentration, and flowability. Continuous, inline monitoring provides immediate data, helping operators optimize processes, ensure product quality, and reduce waste. Manual sampling, in contrast, can be slow to detect deviations and may introduce its risks or inaccuracies.

Beyond process optimization and quality control, density and viscosity data can provide a secondary layer of safety insight. For example, in grain handling, changes in material density can correlate with changes in moisture content. Moisture levels are known to influence dust generation and the explosibility of the dust. Similarly, in slurry-based processes, deviations in density or viscosity can signal issues like particle settling or blockages. If left unaddressed, these conditions could lead to abnormal dust accumulation or operational upsets, indirectly increasing the plant’s overall risk. By using certified-safe sensors to monitor these variables, operators not only ensure the sensor itself is not an ignition hazard but also get an early warning about conditions that could contribute to a broader dust explosion risk, allowing for proactive intervention.

Rheonics offers inline process density meters (SRD) and viscometers (SRV) that are designed for these challenging industrial environments. A key feature of these sensors is their EX certification, which includes approvals for use in areas where combustible dusts are present. This ensures they can be safely integrated into processes without becoming an ignition source.

2. Navigating Hazardous Area Classifications for Combustible Dust: ATEX and IECEx Frameworks

To ensure the safe use of equipment in potentially explosive atmospheres, comprehensive regulatory and certification frameworks have been established. Two of the most widely recognized are the ATEX Directive in Europe and the IECEx System at the international level. Both frameworks are designed to harmonize safety standards and ensure that equipment intended for hazardous areas complies with strict safety requirements.

The ATEX Directive encompasses two main parts: Directive 1999/92/EC (also known as ATEX 137), which outlines the duties of employers to protect workers from explosive atmosphere risks, including the classification of hazardous areas into zones; and Directive 2014/34/EU (also known as ATEX 114), which specifies the essential health and safety requirements and conformity assessment procedures for equipment and protective systems intended for use in these areas. The IECEx System provides an international scheme for the certification of equipment, facilitating global trade by ensuring compliance with IEC standards.

2.1. Defining Dust Zones (ATEX & IECEx)

For environments with combustible dust hazards, both ATEX and IECEx define zones based on the frequency and duration of the presence of an explosive dust-air mixture:

Zone 20: An area where an explosive atmosphere in the form of a cloud of combustible dust in air is present continuously, for long periods, or frequently. This zone demands the highest level of equipment protection (ATEX Category 1D / IECEx EPL Da).
Zone 21: An area where an explosive atmosphere in the form of a cloud of combustible dust in air is likely to occur in normal operation occasionally. This requires ATEX Category 2D / IECEx EPL Db equipment.
Zone 22: An area where an explosive atmosphere in the form of a cloud of combustible dust in air is not likely to occur in normal operation, but, if it does occur, will persist for a short period only. ATEX Category 3D / IECEx EPL Dc equipment is suitable for this zone.

2.2 Understanding Dust Groups (ATEX/IECEx)

Group IIIA: Flammable flying particles (larger particles, typically not requiring the same level of protection as finer dusts).
Group IIIB: Non-conductive dusts. This group includes a vast range of common industrial dusts such as flour, grain, sugar, wood, most plastics, and many non-metallic chemical powders.
Group IIIC: Conductive dusts. This group includes materials like metallic dusts (e.g., aluminum, magnesium), coal dust, and carbon black. Conductive dusts present an additional hazard because they can cause short circuits or create conductive paths, potentially leading to ignition. For context, the North American system classifies explosive dusts under Class II, with Group E for metal dusts, Group F for carbonaceous dusts (like coal or charcoal), and Group G for other dusts such as flour, grain, and plastics.

2.3. Equipment Protection Levels (EPLs) for Dust (IECEx) and Categories (ATEX)

The level of protection afforded by equipment is designated by EPLs under IECEx and Categories under ATEX:

EPL Da (IECEx) / Category 1D (ATEX)

Provides a “very high” level of protection, suitable for Zone 20. Equipment with this rating must ensure safety even in the event of rare (two independent) malfunctions.

EPL Db (IECEx) / Category 2D (ATEX)

Provides a “high” level of protection, suitable for Zone 21. Safety is maintained during normal operation and expected (single) malfunctions.

EPL Dc (IECEx) / Category 3D (ATEX)

Provides a “normal” level of protection, suitable for Zone 22. Safety is ensured during normal operation.

2.4. Temperature (T) Class Ratings and Maximum Surface Temperature for Dust

A critical aspect of hazardous area certification is ensuring that the maximum surface temperature of any equipment remains safely below the auto-ignition temperature of the surrounding explosive atmosphere. For combustible dusts, this is particularly nuanced. The ignition temperature of a dust layer can be significantly lower than that of a dust cloud. Dust can accumulate on equipment, forming insulating layers that may smolder or ignite at lower temperatures than a dispersed cloud. Therefore, equipment intended for dusty areas must be rated based on a maximum surface temperature that is safe for both cloud and layer ignition, with the layer ignition temperature often being the more restrictive value.

Instead of the T1-T6 classes commonly used for gases, dust certifications often specify the maximum surface temperature directly, such as Tmax 85°C or Tmax 135°C. This explicit temperature marking is crucial for users to correctly match the equipment to the specific ignition characteristics of the dust present in their facility. The certification for Rheonics sensors, for example, includes a range of specific maximum surface temperatures (e.g., T85°C, T100°C, etc., as part of the “Ex ia IIIC T… Da” marking), indicating that the selection must be carefully made based on the properties of the actual dust encountered and the ambient operating conditions. This ensures that the sensor surface will not become an ignition source for accumulated dust layers.

Disclaimer

The fact that Rheonics sensors achieve EPL Da and are certified for Group IIIC dusts is particularly noteworthy. Certification for Group IIIC means the sensors are suitable for the most challenging conductive dusts, significantly broadening their applicability beyond just non-conductive Group IIIB dusts. Simultaneously, an EPL Da rating signifies their suitability for Zone 20, the most hazardous dust environment where explosive atmospheres are continuously or frequently present. This dual certification for the highest dust group and protection level underscores their robust safety design for a wide spectrum of demanding applications.

3. Intrinsic Safety (Ex i): A Premier Protection Strategy for Dust-Laden Environments

Intrinsic Safety (IS), or ‘Ex i’, is a protection technique applied to electrical equipment and wiring for hazardous locations. The core principle of IS is to limit the available electrical and thermal energy within the equipment and its wiring to a level below that which can cause ignition of a specific hazardous atmospheric mixture, whether it be flammable gas, vapor, or combustible dust.

Intrinsically safe installation of Rheonics inline viscometer SRV.

This energy limitation is implemented using Zener barriers, installed in a non-hazardous (safe) area or within a certified enclosure. These barriers include components like Zener diodes to restrict voltage, resistors to limit current, and fuses to safeguard circuit elements. For Rheonics sensors, the transmitter must be placed outside the hazardous zone, while the probe can be installed in zone 0/zone 20.

3.1. Levels of Intrinsic Safety (ia, ib, ic)

Intrinsic safety is categorized into three levels, indicating the integrity of safety maintained under fault conditions:

Ex ia (Rheonics sensor certification)

This is the highest level of protection, ensuring safety with up to two independent faults applied to the circuit. Equipment certified ‘Ex ia’ is suitable for use in Zone 0 (for gases) and Zone 20 (for dusts).

Ex ib

This level ensures safety with one fault and is suitable for Zone 1 (gases) and Zone 21 (dusts).

Ex ic

This level ensures safety in normal operation and is suitable for Zone 2 (gases) and Zone 22 (dusts).

3.2. Advantages of Using IS-Certified Equipment in Dusty Hazardous Areas

The application of Intrinsic Safety offers several significant benefits, particularly in environments laden with combustible dust:

Enhanced Safety.

Maintenance.

Cost-Effectiveness.

Simplicity and Weight.

Insurance.

The effectiveness of an Intrinsic Safety system relies on the correct design and installation of the entire “IS loop,” which includes the intrinsically safe apparatus in the hazardous area (e.g., the Rheonics sensor), the associated apparatus (barrier) in the safe area, and the interconnecting wiring. The parameters of the cable (such as its maximum capacitance and inductance) and the characteristics of the sensor and barrier must all be compatible and within the limits specified in the certification documentation. Manuals – Rheonics

4. Rheonics SRD & SRV: Intrinsically Safe Density and Viscosity Sensors with Robust Dust Certification

Rheonics offers a range of inline process sensors, including the SRD (Simultaneous Density Meter and Viscometer) and the SRV (Inline Viscometer), which are engineered for demanding industrial applications, including those with combustible dust hazards. These sensors utilize a patented balanced torsional resonator technology. The SRD measures fluid density based on the shift in the resonator’s natural frequency, while both SRD and SRV determine viscosity by measuring the damping effect the fluid exerts on the resonating element.

Key features of Rheonics SRD and SRV sensors include an all-metal construction (with options for 316L Stainless Steel or Hastelloy C22 for wetted parts), hermetically sealed designs without elastomers, and an inherent insensitivity to mounting orientation or vibrations. They also incorporate built-in fluid temperature measurement, providing comprehensive data for process control.

Detailed Breakdown of Rheonics' EX Dust Certifications (ATEX & IECEx)

Rheonics sensors have undergone rigorous testing and certification to ensure their safe operation in potentially explosive atmospheres, including those with combustible dusts. Their certifications demonstrate compliance with both ATEX and IECEx standards.

Specific Certification Markings for Dust:

The marking for Rheonics Type-SR sensors (SRV and SRD) for dust environments is:

Figure 2: IECEx Explosion classification description

Protection Method

Ex ia – Intrinsic Safety, level ‘a’, suitable for the most hazardous zones.

Dust Group

IIIC – Suitable for all types of combustible dust, including combustible flyings (IIIA), non-conductive dusts (IIIB), and, critically, conductive dusts (IIIC).

Group	Type of Dust	Examples	Conductivity	Explosion Risk	Notes
IIIA	Combustible flyings	Wood chips, fibers, textile fluff	Usually non-conductive	Moderate	Tend to settle quickly, risk of smoldering or ignition.
IIIB	Non-conductive dust	Grain dust, flour, sugar, and plastic powder	Non-conductive	High	Can form explosive clouds. Dust does not conduct electricity.
IIIC	Conductive dust	Aluminum dust, magnesium, metal powders	Conductive	Very high	Highest risk. Conductive dust can cause short circuits, needs special attention.

Maximum Surface Temperature

The operational temperature range of Rheonics sensors defines the safe limits within which the sensor can function reliably and accurately. Choosing the correct sensor variant based on both ambient and process temperatures is essential to ensure measurement stability, mechanical durability, and certification compliance.

In dust hazardous areas (Zone 20, 21, or 22), this becomes particularly important because the sensor’s certified surface temperature rating is directly linked to its defined operational range. If the sensor is operated outside its specified limits, it may exceed its allowable surface temperature and pose an ignition risk to combustible dusts in the surrounding atmosphere.

Thus, while the primary focus is on selecting a sensor that operates within the actual process conditions, doing so also ensures that the sensor maintains its certified surface temperature classification. Always consult Rheonics documentation to confirm compatibility with both temperature conditions and the ignition properties of the dust present in your installation.

Equipment Protection Level (EPL)

Da – “Very High” level of protection, making the sensors suitable for use in Zone 20, where combustible dust clouds are continuously or frequently present.

EPL Code	Applicable Zone	Protection Level	Description
Da	Zone 20	Very High Protection	Equipment remains safe even with two independent faults; suitable for areas where explosive dust atmospheres are continuously present.
Db	Zone 21	High Protection	Safe in the presence of expected disturbances or single faults. Used where dust is likely to occur during normal operation.
Dc	Zone 22	Enhanced Protection	Provides basic protection. Used where explosive dust is unlikely and only occurs briefly or accidentally.

Compliance with Key Standards

The certifications are based on compliance with fundamental international standards, including:

IEC 60079-0 (Explosive atmospheres – Part 0: Equipment – General requirements).
IEC 60079-11 (Explosive atmospheres – Part 11: Equipment protection by intrinsic safety “i”).
The KCs certification for Rheonics sensors explicitly references the IECEx certificate IECEx TUR 19.0005X, issue No. 5.
Compliance with the ATEX Directive 2014/34/EU is also affirmed.

5. Transforming Process Control in Dust Hazard Industries: Applications of Rheonics EX Certified Sensors

Rheonics SRD and SRV sensors, with EX certifications, are well-suited for a multitude of applications across industries where combustible dust poses a significant risk. Their ability to provide real-time, inline density and/or viscosity data allows for enhanced process control, improved product quality, increased efficiency, and, crucially, safer operations.

5.1 Food & Agriculture

Processes

Handling of grains (receiving, conveying, drying, storage), flour milling, sugar refining, processing of cocoa, spices, and powdered milk.

Dust Types

Predominantly Group IIIB dusts like grain dust, flour, sugar dust, starch, spice dusts, and milk powder.

Hazards

High potential for dust explosions in silos, elevators, conveyors, mills, dryers, and packaging areas, often classified as Zones 20, 21, or 22.

Figure 3. Dust hazard applications – Food & Agriculture

SRD/SRV Application:

Density (SRD)

Monitoring bulk density of grains for quality assessment, inferring moisture content, which is critical for safe storage and processing, and optimizing packing efficiency. In processes involving liquid additions (e.g., molasses to animal feed, water to dough) or slurries, the SRD can monitor concentration and solids content.

Viscosity (SRV/SRD)

Controlling the viscosity of batters, doughs, icings, and other liquid or semi-solid ingredients. Monitoring the flowability of powders or granular materials when handled as slurries.

Benefits with Rheonics

The Ex ia IIIC Da certification ensures safe operation in the most hazardous dust zones. For food applications, Rheonics also offers sensors with hygienic designs (EHEDG, 3-A certified ), which is a critical dual compliance. Real-time data aids in optimizing mixing times, ensuring consistent product texture, and reducing waste. For example, in flour milling, monitoring moisture content (inferred from density) during grain conditioning is vital, and controlling slurry/dough viscosity ensures product consistency. ATEX/IECEx classified zones are standard in milling operations.

5.2 Pharmaceutical Manufacturing

Processes

Powder blending, wet/dry granulation, fluid bed drying, tablet pressing, capsule filling, and coating operations.

Dust Types

Active Pharmaceutical Ingredients (APIs) and excipients (e.g., starch, lactose, microcrystalline cellulose). These can be potent, fine, and sometimes sensitive, typically falling under Group IIIB, though some metallic stearates or other compounds could be Group IIIC.

Hazards

Dust clouds can form in mixers, granulators, dryers, tablet presses, and powder transfer systems. Process control is paramount due to high product value and safety concerns.

Figure 4. Dust hazard applications – Pharmaceutical manufacturing

SRD/SRV Application:

Density (SRD)

Monitoring blend homogeneity, granule density (which affects tablet hardness and dissolution), and concentration of solutions or suspensions.

Viscosity (SRV/SRD)

Crucial for controlling the viscosity of coating solutions to ensure uniform tablet coating, managing the consistency of wet granulation slurries, and monitoring suspensions.

Benefits with Rheonics

High accuracy of sensors supports precise formulation and quality control. The Intrinsic Safety protection method allows for easier cleaning protocols and validation processes compared to bulkier Ex d enclosures. The Ex ia IIIC Da certification ensures the highest level of safety when handling fine, potentially potent pharmaceutical powders.

5.3 Chemical Processing

Processes

Manufacturing and handling of a wide range of powdered chemicals, pigments, resins, plastics, and catalysts.

Dust Types

Diverse, including organic powders, plastic dusts (e.g., polyethylene, PVC), metallic powders (often used as catalysts), and carbon black. These can fall into Group IIIB or Group IIIC (e.g., many metal powders, carbon black).

Hazards

Present in reactors, mixers, dryers, pneumatic conveying systems, bagging stations, and storage silos.

Figure 5. Dust hazard applications – Chemical processing

SRD/SRV Application:

Density (SRD)

Monitoring the concentration of solutions and slurries, tracking reaction progress by observing density changes, ensuring final product consistency, and controlling solids content in dispersions.

Viscosity (SRV/SRD)

Controlling the viscosity of polymers during polymerization, managing resin viscosity for applications, ensuring pumpability and consistent mixing of chemical slurries.

Benefits with Rheonics

Robust sensor construction with materials like Hastelloy C22 available for handling corrosive chemicals. Wide operational temperature and pressure ratings suit diverse chemical processes. The Ex ia IIIC Da certification is essential for safety when dealing with conductive or reactive chemical powders.

5.4 Mining and Minerals

Processes

Crushing, grinding, screening, conveying of ores and minerals, slurry preparation and transport, coal handling and preparation.

Dust Types

Coal dust (Group IIIC), various metallic ore dusts (e.g., sulfide ores, which can be conductive – Group IIIC), and rock dust (typically Group IIIB).

Hazards

Pervasive throughout mining and processing plants, especially in enclosed conveyors, crushers, grinders, transfer points, and storage silos.

SRD/SRV Application:

Density (SRD)

Critical for controlling slurry density in pipelines for efficient pumping and water usage management, monitoring concentration in flotation cells, and managing heavy media separation processes.

Viscosity (SRV/SRD)

Monitoring slurry rheology for optimizing pipeline transport (preventing settling, reducing pump wear), and controlling reagent mixing.

Benefits with Rheonics

Rugged sensor design withstands abrasive slurries. The Ex ia IIIC Da certification is indispensable for applications involving conductive coal dust and metallic dusts. Real-time data from SRD/SRV helps optimize water and energy consumption in mineral processing operations.

5.5 Animal Feed Production

Processes

Grinding of raw ingredients (grains, meals), mixing of components, conditioning (steam and moisture addition), pelletizing, cooling, and drying of pellets.

Dust Types

Primarily Group IIIB dusts from grains, soybean meal, fish meal, and various additives.36

Hazards

Dust explosions are a known risk in mixers, grinders, pellet mills, coolers, and conveying systems. Effective dust control is a major operational focus.

SRD/SRV Application:

Density (SRD)

Monitoring bulk density of incoming raw materials, potentially inferring and controlling moisture content in the mash conditioner through density/viscosity changes.

Viscosity (SRV/SRD)

Optimizing the viscosity of the conditioned mash before it enters the pellet mill. Mash viscosity is a key factor influencing pellet quality (durability, hardness, fines reduction) and is controlled by moisture and temperature. Inline viscosity monitoring can significantly improve pellet consistency.

Benefits with Rheonics

Ex ia IIIC Da certification provides the necessary safety assurance. Inline measurement of mash viscosity helps improve pellet durability, reduce fines, and optimize energy consumption in the pelletizing process.

5.6 Wood Processing & Paper Industry

Processes

Sawing, sanding, chipping of wood; pulp preparation (stock preparation, consistency control), paper coating, and drying in paper mills.

Dust Types

Wood dust, sawdust (Group IIIB), paper dust, and fibers (often Group IIIA or IIIB).

Hazards

Significant dust generation in sawmills, furniture factories, and paper mills, particularly around dust collectors, silos, and dryers.

Figure 8. Dust hazard applications – Wood processing & paper industry

SRD/SRV Application:

Density (SRD)

Monitoring wood chip density, critical for pulp consistency and stock preparation in paper making, controlling coating weight.

Viscosity (SRV/SRD)

Controlling the viscosity of paper coatings to ensure uniform application and desired surface properties. Monitoring black liquor viscosity in recovery boilers (though this application often involves gas/vapor hazards as well).

Benefits with Rheonics

Enhanced safety in dusty wood processing environments. Improved consistency in pulp and paper manufacturing through precise density and viscosity control.

5.7 Metal Powders & Additive Manufacturing (3D Printing)

Processes

Production, handling, sieving, blending, and processing of fine metal powders (e.g., aluminum, titanium, stainless steel, nickel alloys) used in powder metallurgy and additive manufacturing (3D printing).

Dust Types

Highly conductive and often very fine metal powders, unequivocally Group IIIC.

Hazards

Extremely high risk due to the low Minimum Ignition Energy (MIE) and high conductivity of these powders. Hazards exist in powder production units, enclosed powder handling systems, sieving stations, and within 3D printing build chambers.

Figure 9. Dust hazard applications – Metal powders & additive manufacturing

SRD/SRV Application:

Density (SRD)

Monitoring the bulk density and tapped density of powders, which affects flowability and packing in AM processes. Monitoring slurry density if powders are processed or delivered in suspension.

Viscosity (SRV/SRD)

Controlling the viscosity of metal powder slurries (e.g., for binder jetting or material extrusion processes) or the viscosity of binder fluids.

Benefits with Rheonics

The Ex ia IIIC Da certification is critical and non-negotiable for these applications, providing the highest level of safety for operations involving highly hazardous conductive metal dusts, even in Zone 20 conditions. The compact sensor size is advantageous for integration into AM equipment or powder processing lines.

5.8 Paints & Coatings (Powder Coatings)

Processes

Manufacturing of powder coatings involves mixing pigments and resins, extrusion, grinding, and sieving. The application involves electrostatic spraying of the powder.

Dust Types

Polymer resin dusts, pigment dusts, typically Group IIIB.

Hazards

Grinding mills, mixers, extruders, spray booths, and powder recovery systems are all areas where explosive dust concentrations can occur.

Figure 10. Dust hazard applications – Paints & coatings

SRD/SRV Application:

Density (SRD)

Monitoring the consistency and density of powder blends before the extrusion and grinding stages to ensure homogeneity.

Viscosity (SRV/SRD)

While less direct for the final dry powder, if liquid precursors or pigment dispersions are used in manufacturing, their viscosity is critical for quality. The SRV/SRD can monitor these upstream liquid phases.

Benefits with Rheonics

Enhanced safety in powder production and handling areas. Improved quality control of liquid precursors or intermediates. The KCs certification specifically mentions “Poussière (peinture, etc.)” (Dust (paint, etc.)) as a relevant industry, underscoring applicability.

5.9 Fertilizer Manufacturing

Processes

Production of granular or powdered fertilizers, including mixing of raw materials, granulation or prilling, drying, and coating of granules.

Dust Types

Dusts from ammonium nitrate, urea, phosphates, potash, and other components. These are generally Group IIIB but can be sensitive or have specific handling requirements.

Hazards

Dryers, granulators, crushers, screens, conveying systems, and bagging stations are common areas for dust accumulation and potential explosion hazards.

Figure 11. Dust hazard applications – Fertilizer manufacturing

SRD/SRV Application:

Density (SRD)

Monitoring the density of slurries before granulation or prilling to ensure correct solids content, controlling the bulk density of the finished granular product for bagging and application consistency.

Viscosity (SRV/SRD)

Controlling the viscosity of fertilizer slurries or melts to ensure consistent granule formation and size distribution. Rheonics documentation indicates the SRV’s use in Fertilizer Manufacturing.

Benefits with Rheonics

Improved product consistency (e.g., granule size, density) and enhanced safety in potentially dusty fertilizer production and handling areas.

6. Reference Table: Rheonics Sensor Suitability in Combustible Dust Applications

The following table provides a consolidated overview of the suitability of Rheonics SRD (inline density and viscosity meter) and SRV (inline viscometer) EX-certified sensors for key applications in combustible dust environments. This table is intended to serve as a quick reference guide for engineers and safety professionals.

Reference Table: Suitability of Rheonics SRD & SRV EX Certified Sensors for Applications in Combustible Dust Environments

Industry Segment	Specific Application / Process	Common Combustible Dust Type(s) & Characteristics	Typical Dust Group (ATEX/IECEx)	Typical Hazardous Zone (ATEX/IECEx)	Recommended Rheonics Sensor	Key Process Parameters Monitored	Benefits & Suitability Notes for Rheonics Sensor	Relevant Rheonics Dust Certification Aspect
Food & Agriculture	Flour Milling - Grain Conditioning & Dough Mixing	Wheat Flour, Corn Starch - fine, organic	IIIB	Zone 20, 21, 22	SRD, SRV	Density, Viscosity, Temperature, Moisture Inference	Optimize moisture for milling via density; control dough viscosity for consistency. Hygienic design available. Safe for continuous dust presence.	Ex ia IIIC T135∘C Da (example, verify specific T based on application)
	Sugar Refining - Crystallization & Syrup Concentration	Sugar Dust - fine, organic	IIIB	Zone 20, 21	SRD	Density, Concentration (Brix), Viscosity	Monitor crystal growth, control syrup concentration. Hygienic design. Safe in high dust areas.	Ex ia IIIC T100∘C Da (example, verify specific T)
	Powdered Milk Production - Spray Drying & Powder Handling	Milk Powder - fine, organic	IIIB	Zone 20, 21	SRD	Density, Viscosity (of concentrate)	Control concentrate feed to dryer; monitor powder bulk density. Hygienic. Safe for explosive powder.	Ex ia IIIC T135∘C Da (example, verify specific T)
Pharmaceuticals	Powder Blending & Granulation	APIs, Excipients (Lactose, Starch) - fine, potent	IIIB (potentially IIIC for some excipients)	Zone 20, 21	SRD, SRV	Density, Viscosity, Blend Homogeneity	Ensure blend uniformity via density; control granulation liquid viscosity. IS for easy cleaning. Max safety for potent dusts.	Ex ia IIIC T85∘C Da (example, verify specific T)
Pharmaceuticals	Tablet Coating	Coating Polymers, Pigments - fine	IIIB	Zone 21, 22	SRV	Viscosity, Temperature	Maintain consistent coating solution viscosity for uniform tablet weight gain and appearance.	Ex ia IIIC T85∘C Da (example, verify specific T)
Chemical Processing	Polymer Powder Production & Handling	Polyethylene, Polypropylene Powders - fine	IIIB	Zone 20, 21	SRD	Bulk Density, Flow properties (inferred)	Monitor powder density for consistency and packing. Safe for flammable polymer dusts.	Ex ia IIIC T135∘C Da (example, verify specific T)
Chemical Processing	Carbon Black Handling	Carbon Black - very fine, conductive	IIIC	Zone 20, 21	SRD	Slurry Density, Bulk Density	Monitor density in production and handling. Essential IIIC rating for conductive dust.	Ex ia IIIC T200∘C Da (example, verify specific T)
Mining & Minerals	Coal Slurry Transport & Preparation	Coal Dust - fine, conductive, abrasive	IIIC	Zone 20, 21	SRD	Slurry Density, Solids Content, Viscosity	Optimize slurry density for pumping; monitor for safety. Robust for abrasives. Essential IIIC & Da for coal.	Ex ia IIIC T135∘C Da (example, verify specific T)
Mining & Minerals	Metallic Ore Processing (e.g., Grinding Circuits)	Metal Sulfide Ores - fine, potentially conductive, abrasive	IIIC / IIIB	Zone 21, 22	SRD	Slurry Density, Solids Content	Control grinding circuit density for efficiency. Robust. IIIC if conductive.	Ex ia IIIC T200∘C Da (example, verify specific T)
Animal Feed Production	Mash Conditioning for Pelletizing	Grain Dusts, Protein Meals - organic	IIIB	Zone 21, 22	SRV, SRD	Viscosity, Density, Moisture (inferred)	Optimize mash viscosity/density by controlling steam/moisture for durable pellets.	Ex ia IIIC T100∘C Da (example, verify specific T)
Wood Processing & Paper	Wood Dust Extraction & Silo Storage	Wood Dust, Sawdust - organic	IIIB	Zone 20, 21	SRD (for chip density/moisture)	Bulk Density, Moisture (inferred)	Monitor chip density for digester feed. Safe for highly flammable wood dust.	Ex ia IIIC T135∘C Da (example, verify specific T)
	Paper Pulp Stock Preparation	Cellulose Fibers - organic	IIIA / IIIB	Zone 21, 22	SRD	Pulp Consistency (Density)	Control pulp consistency for paper machine feed.	Ex ia IIIC T100∘C Da (example, verify specific T)
Metal Powders & Additive Manufacturing	Aluminum/Titanium Powder Handling & Sieving	Aluminum, Titanium Powders - very fine, highly conductive	IIIC	Zone 20, 21	SRD, SRV (for slurries)	Bulk Density, Slurry Viscosity/Density	Critical safety for handling highly explosive metal powders. Highest EPL & IIIC essential.	Ex ia IIIC T200∘C Da (example, verify specific T)
Paints & Coatings	Powder Coating Manufacturing (Grinding/Mixing)	Polymer Resins, Pigments - organic	IIIB	Zone 20, 21	SRD (for blend density), SRV (for liquid precursors)	Density, Viscosity	Ensure blend homogeneity; control precursor viscosity. Safe for paint powder production.	Ex ia IIIC T135∘C Da (example, verify specific T)
Fertilizer Manufacturing	Granular Fertilizer Production (Drying/Coating)	Ammonium Nitrate, Urea, Potash Dusts - organic/inorganic	IIIB	Zone 21, 22	SRD, SRV (for melts/slurries)	Density, Viscosity, Moisture (inferred)	Control slurry/melt viscosity for granulation; monitor bulk density of granules.	Ex ia IIIC T135∘C Da (example, verify specific T)

Note: The specific Tmax value (e.g., T85C, T100C, T135C, T200C, T285C, T485C) from the sensor’s certification must be chosen based on the actual ignition temperature of the specific dust and the maximum ambient/process temperatures. Consult Rheonics documentation for precise selection.

7. Installation and Operational Considerations for EX-Certified Sensors

The safe and effective use of any EX-certified equipment, including Rheonics SRD and SRV sensors, hinges on correct installation, operation, and maintenance in strict accordance with the manufacturer’s instructions and relevant hazardous area standards. Rheonics Manuals

It is imperative that all personnel involved in the installation, commissioning, operation, and maintenance of Rheonics sensors in hazardous areas thoroughly read and adhere to the specific EX installation manual provided by Rheonics. These manuals contain critical information regarding wiring procedures, selection of compatible associated apparatus (barriers), and any “special conditions for safe use” that must be observed. Often, EX certificates will bear an ‘X’ suffix (e.g., TÜV 19 ATEX 8332 X, or IECEx TUR 19.0005X ). This ‘X’ indicates that there are specific conditions, detailed in the certificate schedule or the instruction manual, that are essential for maintaining the safety integrity of the installation. These conditions might include limitations on cable parameters, requirements for mechanical protection, or specific ambient temperature ranges. Failure to comply with these conditions can invalidate the certification and compromise safety.

Intrinsic Safety System Requirements

Rheonics SRD and SRV sensors are certified as intrinsically safe ‘Ex ia’ devices. This means they form part of an intrinsically safe system. Key considerations include:

Associated Apparatus (Barrier)

The sensor must be connected via an approved intrinsically safe barrier (Zener diode barrier or galvanic isolator) that limits the energy transferred from the safe area to the hazardous area. The Rheonics sensor electronics unit, which interfaces with the barrier functionality, must be installed in a designated non-hazardous (safe) area or within an enclosure that is appropriately certified for the zone in which it is located.

Cable Parameters

The capacitance and inductance of the interconnecting cable between the barrier and the sensor must not exceed the maximum values specified in the sensor’s certification documents or the barrier’s documentation. This ensures that the cable itself cannot store enough energy to cause an ignition.

8. Conclusion: Advancing Safety and Operational Excellence in Dusty Environments with Rheonics Certified Sensors

The risk posed by combustible dust in industrial settings demands a rigorous approach to safety, with the selection of appropriately certified equipment being a critical component. It is essential to recognize that not all EX certifications are equivalent; dust-specific considerations such as hazardous area Zones (20, 21, 22), Dust Groups (IIIA, IIIB, IIIC), Equipment Protection Levels (Da, Db, Dc), and crucially, the maximum surface temperature limitations considering dust layer ignition, are paramount for ensuring safety.

Rheonics SRD inline density and viscosity meters and SRV inline viscometers offer advanced measurement technology combined with robust construction. Most importantly for applications in dusty environments, these sensors carry comprehensive and high-level EX certifications, specifically Ex ia IIIC T(range)° C Da. This marking signifies their suitability for use with all types of combustible dusts, including conductive ones (Group IIIC), and in the most hazardous Zone 20 locations (EPL Da), with intrinsic safety ‘ia’ providing the highest level of fault tolerance. The specified range of maximum surface temperatures allows for precise matching to the ignition characteristics of the specific dust hazard.

The adoption of these certified sensors brings multiple benefits. Foremost is the enhanced safety, as the intrinsic safety design prevents the sensor from becoming an ignition source. Beyond this primary safety function, the real-time density and viscosity data provided by Rheonics sensors enable significant improvements in process efficiency, product quality consistency, and can lead to reduced waste and optimized resource utilization. The operational advantages, such as the potential for easier maintenance due to the nature of intrinsic safety, further contribute to their value.

Reference

Disclaimer

Rheonics does not perform hazardous area classification. Rheonics’ scope is limited to the Ex certification of its own sensors and the applicable gas group, temperature classification, and dust classification stated in the product documentation. The assessment and endorsement of hazardous area zoning—whether for gas/vapor or dust hazards—must be carried out by a qualified and authorized entity in accordance with applicable standards and regulations.