What products are involved?

Rheonics SME-DRM sensor electronics, Zener barriers, and SRV/SRD sensors with Rheonics Ex sensor cables.


What is the purpose of this article?

This article explains how to install the SME-DRM and Zener barriers in a cabinet, which cabinets exist for explosive atmospheres, and what is needed in the cabinet: cable glands, power cable and communication ports.


Table of Contents

1. How to Install the SME-DRM in a Cabinet?

  1. The first step is to have an open slot in a DIN rail installed inside the cabinet with enough room for the SME-DRM to be installed.

    SME-DRM dimensions

    Figure 1. SME-DRM dimensions


  2. Verify that we have installed a 35mm DIN rail in the cabinet [1].

    35 mm DIN rail

    Figure 2. 35mm DIN rail


  3. Find the snap clip at the back of the SME, this part will be used to snap the electronics into the DIN Rail.

    Back side of the SME with the DIN rail snap clip

    Figure 3. SME back side.


  4. Follow the installation procedure in Figure 4.

    Procedure for installing the SME-DRM on a DIN rail

    Figure 4. Installation in DIN Rail procedure.


  5. Result when installed in the cabinet.

    SME-DRM installed on a DIN rail

    Figure 5. SME-DRM installed in a DIN RAIL.


  6. An SME-TRD installed inside an explosion-proof (Ex d) enclosure might look like this.

    SME-TRD sensor electronics installed inside an explosion-proof enclosure with a sight glass

    Figure 6. SME-TRD installed inside an explosion-proof (Ex d) enclosure with sight glass


2. How to Install SME-DRM with Zener Barriers?

Zener barriers are necessary for an intrinsically safe system for the protection of other people and instruments. Zener Barriers and SME-DRM should be installed always in a Safe Zone [2] and follow the recommendations from this support article. Topology wiring for Ex sensors

The way to install the SME-DRM is the same as described in the previous section, the same process must be followed with the Zener Barriers as those also compatible with DIN Rails.

Zener Barriers with DIN rail support must be installed as recommended in their user manuals, for example, P+F suggests the following step to correctly snap the Barrier to the rail [3].


Zener barrier snapped onto a DIN rail

Figure 7. The Zener barrier snapped into a DIN Rail


3. What Kind of Cabinets Exist Based on Protection Ratings When Used in Explosive Atmospheres?

The SME-DRM and the Zener barriers are always installed in the safe zone [2]. This section describes the enclosure types used in explosive atmospheres for reference only.


3.1 Europe (ATEX)

ATEX-certified enclosures can be manufactured in stainless steel and GRP with various explosion protection concepts, including Increased Safety (Ex e), Flameproof (Ex d), and Intrinsic Safety (Ex i). [4]


3.1.1 Increased Safety (Ex e)

Increased Safety Ex e refers to the concept of explosion protection that is applied to electrical systems in hazardous areas to prevent excessive temperatures and sparks. This method of explosion protection excludes equipment that normally causes sparks. [5]


Stahl Ex e enclosure

Figure 8. Stahl Ex e enclosure[6]


3.1.2 Explosion Proof (Ex d)

During an internal explosion, an Ex d enclosure prevents flames, sparks, and hot gases from escaping into the atmosphere. Also, Ex d enclosures protect the fitted equipment against dirt, dust, and moisture. [7]


Ex d IIB+H2 enclosure, series EJB

Figure 9. Ex d IIB+H2 Enclosure Series EJB[8]


3.2 US (NEMA)

The NEMA provides a rating system for electrical enclosures that explains how the enclosure will perform in certain conditions. NEMA standards benefit both the user and the manufacturer while improving safety and communication. [9]

The NEMA enclosure type that is truly explosion-proof is NEMA 7 [10]. NEMA 7 is “designed to contain an internal explosion without causing an external hazard.”[11]

The National Fire Protection Association (NFPA) releases the National Electric Code (NEC) 70, which establishes criteria for identifying hazardous locations using a framework of classes, divisions, and groups. These classifications are used to designate enclosures and equipment suitable for deployment in these areas. The categorization of hazardous areas takes into account the nature of substances or materials found in the area, their probability of presence, and more specific factors like ignition temperatures and explosive characteristics. [11], [12]


Class and Hazardous MaterialDivisionGroup
Class I
Gases or vapors(acetylene, hydrogen, ethylene, propane)

Division 1

  • Under normal operating conditions.
  • As a result of frequent maintenance operations, repair operations, or leakage.
  • As a result of equipment breakdown, faulty operation, or failure.

Division 2

  • Normally confined within closed containers when handled or used.
  • Normally prevented by positive mechanical ventilation
  • Be adjacent to a Class 1, Division 1 location

A: Acetylene

B: Butadiene. Ethylene oxide. Hydrogen. Propylene oxide.

C: Acetaldehyde. Cyclopropane. Diethyl Ether. Dimethyl Hydrazine.

D : Acetone. Ammonia. Benzene. Butane. Gasoline. Methane. Propane. Alcohols. Etc

Class II
Combustible Dust

Division 1

  • Under normal operating conditions.
  • As a result of frequent maintenance or repair work.
  • As a result of frequent mechanical failure or abnormal operation of equipment

Division 2

  • Under abnormal conditions, such as abnormal operation/failure of equipment
  • As a result of infrequent malfunctioning of handling or processing equipment

E: Combustible metal dusts(aluminium. magnesium, and their commercial alloys

F: Combustible carbonaceous dusts(carbon black, charcoal,coal & coke)

G: Combustible dusts not in groups E or F(flour, grain, wood, plastic & chemicals)

Class III
Ignitable Fibers

Division 1

  • Handled, manufactured or used in this environment & may be present.

Division 2

  • Stored or handled in this environment & may be present
No Equivalent

Table 1. Hazardous area classification


In gas atmospheres, Division 1 covers both Zone 0 and Zone 1, and Division 2 corresponds to Zone 2. Equipment listed and marked for Zone 0, 1 or 2 is permitted in a Division 2 location, and equipment listed for Zone 0 is also permitted in Division 1, for the same gas and with a suitable temperature class. These rules are set out in the National Electrical Code (NFPA 70) [13].


3.2.1 NEMA Type 7

It is designed to contain an internal explosion without causing an external hazard.

These enclosures are intended for indoor use in hazardous locations classified as Class I, Division I, Groups A, B, C, or D.


NEMA 7 enclosure, Appleton EDS3036

Figure 10. Appleton EDS3036 explosionproof disconnect switch in a NEMA 7 enclosure [14]


3.2.2 NEMA Type 9

It is designed to prevent the ignition of combustible dust. Type 9 enclosures are intended for use indoors in the atmospheres defined as Class II, Division I, and Group E, F, or G in the National Electrical Code.


Hoffman NEMA Type 9 enclosure

Figure 11. Hoffman enclosure NEMA Type 9[15]


3.2.3 NEMA Type 8 and Type 10

There are two additional types of enclosures engineered to avert ignition and safely confine explosions, and these cater to more specialized applications, namely NEMA Type 8 and Type 10.

NEMA Type 8 enclosures are designed to prevent combustion through the use of oil-immersed equipment. Type 8 enclosures are intended for use indoors, in the atmospheres and locations defined as Class 1, Division I and Group A, B, C or D in the National Electrical Code.

NEMA Type 10 enclosures are designed to contain an internal explosion without causing an external hazard. Enclosures constructed to meet the requirements of the Mine Safety and Health Administration, 30 CFR, Part 18


3.3 IECEx

The IECEx System is based on the use of International Standards, such as IEC Standards and ISO Standards. These Standards are dedicated to the highly specialized fields associated with the use of equipment, termed Ex equipment, and installations in areas where a potential may exist of fire or explosion.[16]


3.4 Others

In Russia, the EAC Certification(Eurasian Conformity Certification) of Explosion-proof equipment is available. The EAC EX certificate for explosion-proof equipment may only be issued by a notified body accredited by the Federal Office for Technical Regulation and Metrology (Rosstandart).[17]

In China, China's central authority CNCA (Certification and Accreditation Administration) organizes and supervises CCC certification in conjunction with SAMR (State Administration for Market Regulation). A major authority for CCC-Ex certification is SITIIAS (Shanghai Inspection and Testing Institute of Instruments and Automation Systems) – sometimes referred to as NEPSI (National Supervision and Inspection Center for Explosion Protection and Safety of Instrumentation).[18]

In Brazil, the local ordinance, Portaria INMETRO 115:2022, establishes the requirements for selling hazardous locations products in Brazil. In hazardous locations, electrical and electronic equipment must comply with this regulation.[19]

In India, PESO certification is India’s equivalent of ATEX or IECEx certification. Strictly speaking, one of the two certificates for explosion-proof products is required for successful PESO certification. [20]

In Japan, Electrical equipment made available on the Japanese market or installed in hazardous locations is subject to JPEx certification.[21]

In Korea, the Korea Occupational Safety and Health Agency (KOSHA) provides the KCs Ex certification of explosion-proof electrical components.[22]

4. What Is Needed in Cabinets?

Rheonics SME-DRM is ready to be installed inside enclosures alongside Zener barriers if necessary and the procedure for the installation is easy and intuitive.


Video 1. Enclosure for Rheonics Sensor electronics and Zener barriers (NEMA box)


4.1 Cable Glands in a Cabinet for Sensor Cable

The cable gland is a connector used to secure cables to plugs, terminals, enclosures, or electrical equipment. It can be used to protect sensitive electrical wiring against moisture, contamination, corrosion, and even flames. Figures 12 and 13 showcase cable glands that are used to pass the sensor, communication, and power cables from outside to the inside of the cabinet which contains the sensor electronics and EX barriers.


Schematic of an SME-DRM in an ATEX cabinet, with the sensor cable passing through a cable gland to an SRV sensor

Figure 12. Schematic showing SME-DRM installed in an ATEX cabinet with sensor cable coming through a cable gland and connected to an SRV sensor.


Schematic of an SME-DRM in an ATEX cabinet, with the sensor cable passing through a cable gland to an SRD sensor

Figure 13. Schematic showing SME-DRM installed in an ATEX cabinet with sensor cable coming through a cable gland and connected to an SRD sensor.


It is recommended that cable glands must be tested using samples of the proposed cable type(s) before they can be approved for use in the intended hazardous location. The parts of the cable glands can be found below:


Cable gland parts

Figure 14. Cable gland parts [23]


We need to select the cable gland based on the following criteria:


4.1.1 Size of the Ex-Sensor Cable

To select the right cable gland, you must determine the cable's size and type. A cable gland's diameter will be determined by its cable size.


Cable gland

Figure 15. Cable gland


The SRV/SRD sensor is connected to its associated Zener diode barriers via a cable with an 8-pole M12 connector.


Ex sensor cable built by Rheonics

Figure 16. Ex Sensor cable built by Rheonics.


The end that connects to the Zener diode barrier must be provided with crimped conductor-end sleeves, which are held by screw clamps on the Zener diode barriers. The cable and connector selected must be rated for at least the highest ambient temperature at which the sensor will be used.

Rheonics Ex sensor cables can be provided up to a maximum length of 500m (1,640 ft) [2].


Ex sensor cable for intrinsically safe applications

Figure 17. EX sensor cable used for Intrinsically safe application with the Rheonics sensor.


4.1.2 Consider the Environment

For cable glands to be approved for use in hazardous locations, they must be tested using samples of the proposed cable type(s).

Each hazardous location (Division 1 or Division 2) has its cable gland requirements, including the type of features and whether the cable gland must be sealed. Under NEC & CEC wiring practices, explosion-proof cable glands must be capable of incorporating an integral barrier seal[24].


4.1.3 Cable Gland Used in a Cabinet for Power and Communication (Depends on Customer Requirement)

When selecting cable glands for a cabinet that will house both power and communication cables, you need to ensure that the chosen cable glands provide proper protection, organization, and separation for both types of cables. A few cable glands that can be used in the Hazardous zone are the following:


Explosive atmosphere barrier cable gland PXSS2K

Figure 18. Explosive Atmosphere Barrier Cable Gland PXSS2K [25]


M20 ATEX cable gland, nickel-plated brass

Figure 19. M20, Atex Gland, Nickel Plated Brass[26]


Here are some recommendations specifically for using cable glands in a cabinet for power and communication cables:

  1. Consider using separate cable glands within the cabinet for power and communication cables. This helps prevent interference between the two types of signals and reduces the risk of electromagnetic interference (EMI).
  2. Choose cable glands with an appropriate IP rating to prevent dust, dirt, and moisture from entering the cabinet. The IP rating should match the environmental conditions where the cabinet will be installed.
  3. Select cable glands made from suitable materials, such as stainless steel or nickel-plated brass, to ensure durability and protection against environmental factors.
  4. Ensure that you have proper grounding for both power and communication cables. Grounding cables should be properly managed and may require separate grounding points.
  5. Plan the entry points for the cables in a way that minimizes the risk of tangling or stress on the cables. Cable glands with proper strain relief mechanisms can help achieve this.
  6. Use cable glands that allow for easy separation and organization of power and communication cables. Cable management accessories like grommets, cable ties, and cable organizers can be helpful.
  7. Ensure that the cable glands can accommodate the different sizes of power and communication cables you plan to use in the cabinet.
  8. For communication cables, consider cable glands that offer electromagnetic interference (EMI) and radio-frequency interference (RFI) shielding to minimize signal interference.
  9. Plan for potential future cable additions. Choose cable glands that can accommodate additional cables if needed.
  10. Cable glands with sealing features (compression seals, O-rings, etc.) protect against dust, moisture, and other environmental factors that could compromise cable integrity.


Always refer to the specific requirements of your project and consult with experts in cable management, electrical engineering, and cabinet design to ensure that the selected cable glands meet your needs and comply with relevant industry standards and regulations. Visit our support article: Cable protection on Rheonics Sensor


4.1.4 Recommendation on the Power Cable

To power the electronics of 5 W, your power cable should be able to provide 24V DC, 200 mA maximum, with a supply able to provide at least 400 mA [27]. It is important to select a cable with the voltage drop in mind and select the cable gauge to ensure the voltage supplied at the electronics' end meets the requirement. Voltage drop becomes significant over longer cable lengths, potentially impacting the voltage received by the electronics but in general, a cable of 16 to 20 AWG could be used with our electronics. The installer is responsible for sizing the power cable according to local regulations.


4.1.5 Recommendation on the 4-20mA Output

When using the 4-20 mA output from the sensor, check our support article: What can go wrong with 4 - 20mA loops ?


4.1.6 Recommendation on the Ethernet Port

When using the Ethernet port from the sensor, check our support article: Introducing Ethernet connections on SME


4.1.7 Recommendation on the RS-485 Port

When using the RS-485 port from the sensor, check our support article: Connecting Modbus RTU (RS-485) outputs

5. USB Port Access

USB Connection to the Transmitter

6. Display Mounting

Transmitter Display Module installation instructions (SME-TRD)

7. References

  1. Ferrules Direct, "TH35-7.5T - Top Hat Style DIN Rail for Terminal Blocks, 35mm x 7.5mm, Galvanized Steel, 1 Piece." [Online]. Available: https://www.ferrulesdirect.com/products/th3575t. [Accessed: Sep. 23, 2026].
  2. Rheonics GmbH, Rheonics EX i SRV SRD Installation and Intrinsic Safety Manual, V4.2. [Online]. Available: https://rheonics.com/wp-content/uploads/2025/07/Rheonics_EX-i_SRV-SRD_Installation-and-Intrinsic-Safety-Manual_V4.2_English.pdf. [Accessed: Sep. 23, 2026].
  3. Pepperl+Fuchs, "Manual Z-System Zener Barriers." [Online]. Available: https://files.pepperl-fuchs.com/webcat/navi/productInfo/doct/tdoct0185j_eng.pdf?v=20230511084829. [Accessed: Sep. 23, 2026].
  4. Heating and Process, "ATEX Enclosures | ATEX Junction Box | Zone 1 Zone 2 Enclosure." [Online]. Available: https://www.heatingandprocess.com/product/junction-boxes-enclosures-atex-hazardous-area-zone1-zone2/atex-enclosures/. [Accessed: Sep. 28, 2026].
  5. Heating and Process, "Ex e Increased Safety | Explosive Atmospheres Explosion Proof Protection." [Online]. Available: https://www.heatingandprocess.com/product/product-category/ex-e-increased-safety/. [Accessed: Sep. 23, 2026].
  6. R. STAHL, "Boîtes de jonction Ex e robustes et flexibles en acier inoxydable." [Online]. Available: https://r-stahl.com/fr/fr/produits/boites-de-derivation-et-boites-de-jonction/boites-de-jonction-ex-e-acier-inoxydable/. [Accessed: Sep. 23, 2026].
  7. Extronics, "What is an Ex d Enclosure?." [Online]. Available: https://www.extronics.com/blog/what-is-an-ex-d-enclosure/#:~:text=An%20Ex%20d%20enclosure%20is,dirt%2C%20dust%2C%20or%20water.. [Accessed: Sep. 23, 2026].
  8. ROSE Systemtechnik GmbH, "Ex d IIB+H2 Enclosure Series EJB." [Online]. Available: https://www.rose-systemtechnik.com/en/products/ex-equipment/ex-enclosure-systems/ex-d-enclosure-series/ex-d-iibh2-enclosure-series-ejb/. [Accessed: Sep. 28, 2026].
  9. Schneider Electric, "What Is “NEMA”?." [Online]. Available: https://www.se.com/us/en/work/featured-articles/what-is-nema/. [Accessed: Sep. 28, 2026].
  10. Intrinsically Safe Store, "Explosion Proof: Nema 4X Ratings Explained For Hazardous Areas." Archived Sep. 9, 2025. [Online]. Available: https://web.archive.org/web/20250909073158/https://intrinsicallysafestore.com/blog/what-nema-rating-is-explosion-proof-what-is-nema/. [Accessed: Sep. 28, 2026].
  11. Nema Enclosures, "Electrical Enclosure Types, Non Hazardous Location: Environmental Rating Standards Comparison." [Online]. Available: https://www.nemaenclosures.com/wp-content/uploads/2026/01/NE-NEMA-vs-UL.pdf. [Accessed: Sep. 28, 2026].
  12. ISC Sales, "The Definitive Guide To Hazardous Location Enclosures." [Online]. Available: https://iscsales.com/blog/hazardous-location-enclosures-the-definitive-guide/. [Accessed: Sep. 28, 2026].
  13. National Fire Protection Association, NFPA 70: National Electrical Code. [Online]. Available: https://www.nfpa.org/70. [Accessed: Sep. 28, 2026].
  14. McNaughton-McKay Electric Company, "Appleton EDS3036." [Online]. Available: https://www.mc-mc.com/Product/appleton-eds3036?option=EGSMEDS3036. [Accessed: Sep. 28, 2026].
  15. nVent HOFFMAN, "NEMA Type 9, 12.00x10.00x6.00, Gray, Steel (ENCA12D106)." [Online]. Available: https://www.nvent.com/en-us/hoffman/products/enca12d106. [Accessed: Sep. 28, 2026].
  16. IECEx, "Standards." [Online]. Available: https://www.iecex.com/resources-and-news/standards/. [Accessed: Sep. 28, 2026].
  17. Schmidt & Schmidt, "EAC Certification of Explosion-proof equipment." Archived Feb. 23, 2024. [Online]. Available: https://web.archive.org/web/20240223025952/https://schmidt-export.com/eac-certification/eac-certification-explosion-proof-equipment. [Accessed: Sep. 28, 2026].
  18. MPR China Certification, "CCC-Ex Certification for Explosion-Proof Products in China." [Online]. Available: https://www.china-certification.com/en/certification-for-ex-products/. [Accessed: Sep. 28, 2026].
  19. UL Solutions, "INMETRO Hazardous Areas Certification for Brazil." [Online]. Available: https://www.ul.com/services/inmetro-hazardous-areas-certification-brazil. [Accessed: Sep. 23, 2026].
  20. ERA Certification, "PESO Certification." Archived Jan. 23, 2025. [Online]. Available: https://web.archive.org/web/20250123182539/https://www.era-certification.com/en/peso-certification/. [Accessed: Sep. 28, 2026].
  21. Intertek, "JPEx Certification for Japan." [Online]. Available: https://www.intertek.com/hazardous-locations/jpex-certification/. [Accessed: Sep. 23, 2026].
  22. MPR Korea Certification, "KCs Ex Certification for explosion proof products." [Online]. Available: https://www.korea-certification.com/en/kcs/kcs-ex-certification-for-explosion-proof-components/. [Accessed: Sep. 28, 2026].
  23. CMP Products Limited, "Key Features of CMP Cable Glands." [Online]. Available: https://www.cmp-products.com/cable-glands/technical/cable-glands/key-features-cmp-cable-glands/. [Accessed: Sep. 28, 2026].
  24. CMP Products Limited, "Cable Glands permitted under NEC & CEC wiring rules." [Online]. Available: https://www.cmp-products.com/cable-glands/technical/americas-specific-nec-and-cec/cable-glands-permitted-under-nec-cec-wiring-rules/. [Accessed: Sep. 23, 2026].
  25. CMP Products Limited, "PXSS2K | Ex eb, Ex db, Ex nR, Ex ta | Explosive Atmosphere Barrier Cable Gland." [Online]. Available: https://www.cmp-products.com/glands/products/explosive-atmosphere/pxss2k-explosive-atmosphere-cable-gland/. [Accessed: Sep. 28, 2026].
  26. Mencom, "M20, Atex Gland, Nickel Plated Brass, 0.234 - 0.468." [Online]. Available: https://www.mencom.com/m20-atex-gland-nickel-plated-brass-0-234-0-468.html. [Accessed: Sep. 28, 2026].
  27. Rheonics GmbH, Rheonics SRV Inline Viscometer Manual, DocID SRV-G1-OP-2606, Jun. 2026.