What products are involved?


For SME-DRM (DIN rail mount) transmitter. Visit our product page to learn more about the full features.

Visit Rheonics product page:Products » inline fluid viscometer and density meter 

What is the purpose of this article?

To give guidance and good practices when preparing Rheonics EX intrinsically safe sensor cable with a crimp of length 8mm and terminal diameter 1mm. The terminals of the SME are rated for wires of 0.2 - 1.5 mm2 i.e. AWG 24 - 16.

Normally, Rheonics provides the Ex cables completely assembled and ready for installation, so the user can omit the next sections and only focus on the proper wiring. For cases where the Ex cables are not delivered assembled with the M12 connector and pin ferrules (i.e. when Rheonics delivers a roll of cable for many custom lengths), follow the next sections.

Figure 1. Intrinsically Safe Viscometer.

1. Tools and BoM list


  •  Crimping Tool

Crimping tools are used to deform materials and create connections. To connect wires together or to other connectors, crimping is commonly used in electrical work.

Figure 2. Crimping Tool - 24-10 AWG.[1]
  •  Precision Micro Wire Cutter

A wire cutter or cable cutter is a tool that cut wires and cables in a safe manner without damaging the insulation or conductors.

Figure 3. Precision Micro Wire Cutter. [2]
  •  Measuring Tape

A Measure Tape is a tool used to measure length.

Figure 4. Measuring Tape.[3]
  •  Stripping tool

Wire strippers are portable handheld tools used by workers, especially electricians, to remove the protective coating of electric wires for replacement or repair.

Figure 5. Stripping tool.[4]
  •  Knife

A tool used to cut wires or cables.

Figure 6. Knife. [5]
  •  Soldering Equipment

A durable, permanent connection can be created by joining conductive metal elements with solder. Soldering machines are essential tools for building, modifying, and repairing electronics.

Figure 7. Soldering Equipment.[6]
  •  Hot air gun

Heat guns are devices that emit a jet of compressed air toward a particular point or surface.

Figure 8. Hot air gun.[7]

BoM list

Item name

Manufacturer name 

Manufacturer Part number

Vendor Part number




RND 465-00566



Solder wire




Industrial Solutions | RS formerly known as RS Components 

Heat Shrink tube




Industrial Solutions | RS formerly known as RS Components 

Ex Sensor cable

Helu Kabel type



Productdetails | HELUKABEL 

M12 Connector

Phoenix Contact



SACC-M12FS-8QO-0,5 SH - Connector - 1414611 | Phoenix Contact 

Metal tape





  • Ferrule

Correct ferrule size must be selected based on the gauge of the wire, as a standard Rheonics uses ferrule with a pin length of 8mm and diameter of 1mm (cross-section 0.5mm2).

Figure 9. 22 AWG (8mm Pin) Insulated Ferrules [8]
  •  Solder wire

Solder wires are wires with a low melting point, used to create joints using a soldering iron.

Figure 10. Solder wire[9]
  •  Heat shrink tube

Heat shrink tubing is a common element in most electrical installations that protects wires from moisture, dust, abrasion, and sharp objects that might otherwise damage them.

Figure 11. Hear shrink tube[10]
  • Ex Sensor Cable

The SRV/SRD sensor is connected to its associated Zener diode barriers by means of a cable that has an 8-pole M12 connector on the sensor end.

The cable and connector selected must be rated for at least the highest ambient temperature at which the sensor will be used.

Figure 12. Ex sensor cable[11]
  • M12 connector of the sensor

Connector, Universal, 8-position, halogen-free, shielded, Socket straight M12, A-coded, Insulation displacement connection, knurl material: Zinc die-cast, nickel-plated, external cable diameter 5 mm ... 9.7 mm

Figure 13. M12 connector[12]
  • Metal tape

This tape is commonly used to secure duct seams, connections, and joints. Additionally, it has excellent waterproof properties.

Figure 14. Metal tape.

End result

Once all the steps are completed we are going to obtain our Ex sensor cable with the following three sections. 

Figure 15. Ex Sensor cable built by Rheonics.
2. Probe side - Sensor cable preparation for M12 connector

Required tools:

  1. Knife

  2. Measurement tape

  3. M12 Connector

  4. Metal tape

There is a video available from supplier showing the connection of the M12 connector in the cable, see: Circular connectors for data and signals – SACC QUICKON

  • Take the cable and cut the required length for your application. We recommend stripping out the cable sheath at 80mm from the end as a suitable length to prepare the cables for the M12 connector.

Figure 16.  The sensor cable after the cable sheath is stripped away on the first 80mm.
  • Since the sensor cable has an outer diameter of about 8.5 mm, the cable's shield must be fixed
    with the provided metal tape as shown in the instructions for cable with a diameter over 6 mm. 

Figure 17. Sensor cable fixed with metal tape.
  • After the cable shield has been fixed, the rest of the shield can be cut at the edge of the tape. Then pass all 8 wires of the cable through the sensor body. Take care not to damage the insulation of the wires. Push the cable completely into the sensor connector to ensure proper contact with the cable shield.

  • The connector body has 8 color marked slits in the front. Pull each wire into the slit marked with its
    color as shown in Figure 19.

Figure 18: The connector body is shown from the front. It has 8 slits which are color marked according to wire color.
  • Cut the remnant of each wire, so each wire is fixed in the available space.

    Figure 19. The connector body in front view after the wires have been shortened. 
    • Close the sensor connector.

Figure 20. The sensor connector when it is closed.
  • After the sensor connector has been mounted on the blue sensor cable, it can be connected to the M12 male port of the sensor probe. 

3. SME electronics side - Sensor cable preparation for EX zener barriers


  1. Knife

  2. Cutter

  • Strip the blue outer cable sheath on a length of 100 mm (4 in.).

Figure 21: Preparation of the sensor cable to connect it to the Zener barriers. 
  •  After the stripping of the cable sheath, carefully loosen and then twist the cable shield. 

Figure 22. Twisted cable shield.
  • Remove the plastic cover from the colored wires.

Figure 23. Removing the plastic cover from the wires.

3.1. Preparing grounding cable


  1. Soldering machine

  2. Solder wire

  3. Heat Shrink tube

  4. Hot air gun

  • Take the twisted cable shield and cover it fully with a heat shrink.

  • Take the twisted cable shield and cover it fully with a heat shrink.

Figure 24. Metal shield twisted with heat shrink.
  • Crimp a ferrule to the ground cable end.

Figure 25. Ferrule crimped to the ground cable

3.2. Installing crimpers in each sensor wire


  1. Crimping tool

Your crimping tool should have a nest for inserting the terminal. After inserting in the correct slot, squeeze the crimp tool firmly and release it to get a long-lasting, tight fuse. 

Unused wires should be neither stripped nor crimped. We recommend protecting the ends with a shrink tube to avoid the ends making any electrical contacts.

We recommend crimping the ferrules on 4 sides for the connection with the Zener barriers.

  • Twist the wire and Crimp them (Crimpers) using the Crimping Tool.

Figure 26. Crimping the wire end.
  • The green and yellow wires are not used to operate the sensor. They have to be connected to the
    ground together with the shield of the cable. This means that they should be connected to the ground terminals of the Zener barriers.

Figure 27. Strip all eight wires on a length of 10 mm and put bootlace ferrules on the ends. 
  •  Strip all eight wires on a length of 10 mm and put bootlace ferrules on the ends.

Figure 28. Wire ends stripped with crimped ferrules.
4. Ex zener barriers to SME connection

Next is the connection of the Zener barriers with the SME-DRM, the blue end is used to connect to the sensor that is installed in the hazardous area.

Figure 29. The connection between Zener barriers and SME-DRM


  1. Various wires with crimped ends.

  2. Zener barriers Z041x2 and Z757.

  3. SME-DRM

  • Install the SME-DRM and the Zener barriers in a DIN-rail and prepare short wires to be used.

Figure 30. Short wires.
  • Next is to have a proper grounding, which could be either the DIN-rail or the ground available in the Zener barriers.

Figure 31. Zener barrier grounding.
  • The wiring should be done the same as the wiring diagram shown in Figure 28 Part A. The end result should be as follow.

Figure 32. Zener Barrier wired with SME-DRM.
5. Ex sensor to zener barrier


  1. Ex Sensor cable with crimped ends.

  2. Zener barrier Z041 x 2 and Z757

  3. SME-DRM

  • This step starts with the wiring of each ferrule end with the connection of the Zener barrier, we need to connect each wire to the corresponding terminal in the Zener barrier based on this wiring diagram where the Part B represents the ferrule ends prepared.

Figure 33. Wiring diagram with Pt1000 installed, 4-wire Pt1000 connection
  • The final result should look like this.

Figure 34. Full wiring of the SME-DRM+Zener Barriers+Ex Sensor cable.


  • Typically SME-DRM is used for connection with EX barriers so both can be mounted inside a cabinet with DIN rails

Figure 35. SME-DRM

However, it is also possible to put the EX barriers in another enclosure and connect to the SME-TR or SME-TRD using cable glands. 

  • The barrier can also be used in an enclosure and a cable can be connected between barrier and the SME-TR/TRD through cable glands. 

Figure 37. Zener barriers are used in an outdoor enclosure when using the SME-TRD(Temporary image)


[1] Crimping Pliers for Wire Ferrules 

[2] Precision Micro Wire Cutter - Cutting Range: 28-14 AWG 

[3] How To Read Measure Tape | Reading A Tape Measure | Measuring Tape Reading 

[4] FD2810WS - Wire Cutting and Stripping Tool - 28AWG to 10AWG
[5] Uline Steel Knife in Stock - ULINE 

[6] SCHOFIC 936D Plus Rework Soldering Station SMD Desoldering Solder Iron Handle ESD Soldering Kit Soldering Machine Soldering Iron Kit Soldering Stand 

[7] RS PRO EOT0202 500°C max Corded Heat Gun, Type C - EuroPlug 

[8] https://www.distrelec.ch/en/bootlace-ferrule-5mm-white-14mm-pack-of-100-pieces-rnd-connect-rnd-465-00566/p/30110345 

[9] RS PRO Wire, 0.71mm Lead solder, 183°C Melting Point 

[10] HellermannTyton Heat Shrink Tubing, Black, Blue, Green/Yellow, Red, White 3mm Sleeve Dia. x 35mm Length 3:1 Ratio 

[11] Productdetails | HELUKABEL 

[12] SACC-M12FS-8QO-0,5 SH - Connector - 1414611 | Phoenix Contact 

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