What products are involved?
The SR-Type Rheonics sensor probes, SRV viscometer and SRD density and viscosity meter.
What is the purpose of this article?
Define and compare international organizations dealing with hygienic industrial designs and review Rheonics hygienic certificate.


Industries like Food and Beverage or Pharmaceutical need to follow specific requirements in their production lines so the quality of end products is preserved. As part of the requirements, all equipment included in the production needs to be designed following national or international hygienic standards, so that proper cleaning and sanitizing are achieved.

Multiple organizations develop standards for sanitary and hygienic design in the industry. For example, EHEDG and 3-A are well-known organizations that share the same purpose, to provide and standardize requirements for hygienic design, but differ in content, how certification is granted and the location where they are mainly used. Let’s review them closely.

Rheonics have sensors available with EHEDG certification, and have 3-A certification in progress. 

Figure 1: Rheonics viscometer SRV hygienic variants.



The European Hygienic Engineering & Design Group is a non-profit organization founded in 1989. Its main objective is to promote food safety and quality across the food and beverage industry based on 42 guidelines that deal with specific principles in the design, construction, operation and maintenance of equipment involved in this industry. EHEDG certification requires a theoretical review of the design and a standardized cleaning test. EHEDG’s guidelines are widely used, mainly in Europe, by food companies for food safety regulations, thus improving food safety performance.


This non-profit US-based organization was founded in 1978 and is focused on ensuring and improving hygienic designs in the dairy food, beverage, and pharmaceutical industries using very specific technical principles. Design features such as angles, radii, dimensions, surface smoothness, etc. should match 3-A standards for certification. The objective of this organization is to protect products from contamination and ensure all equipment’s surfaces in contact with the product can be mechanically cleaned and easily dismantled so it favors manual cleaning and inspection.



  • Geographic focus: EHEDG has a more European approach while 3-A is focused in the US and other parts of the world.
  • Design requirements: There are some key differences in the requirements each organization has, so there are no technical equivalences between them. EHEDG details guidelines of design, it doess not specify technical requirements but rather an intended result verified by tests. On the other hand, 3-A provides standards rather than guidelines and is very detailed in the technical features to follow. It can be said that EHEDG covers a broader application range. 
  • Certification requirements: 3-A requires a theoretical review of the design so it follows its standards. EHEDG requires both a theoretical and practical review with a standardized cleaning test of the equipment.

  •  Mission: Despite the differences explained before both EHEDG and 3-A have a similar mission, which is to promote food safety through hygienic design guidelines/standards for the industry.

Rheonics sensors and Hygienic installations

Rheonics SR sensor must be installed according to the requirements given in EHEDG Guidelines 8, 10 and 37 [1-3]. Review Rheonics EHEDG installation guidelines in its web page here

Some of the most noticable requirements are:

  • In tee pieces: the ratio between upstand (L) and the diameters difference (D − d) shall be in the relation of (D − d)/L ≥ 1. See figure below for reference.

Figure 2: Rheonics hygienic installation in standpipes.

  • For the SRD, density and viscosity meter: Place the SRD end probe tip aligned with the fluid flow’s lines to create a parallel flow (see Figure below). This recommendation is relevant when the angle α, formed by the fluid’s flow lines and sensor tip axis, is 90° or less. When α is 0° the installation creates an axial flow, in which case the end tip orientation is not relevant anymore. Perpendicular flow must be avoided because it affects the cleaning process, as shown in next Figure too. 

  • Once the probe is installed, the tip is not visible to know if it is aligned. To solve this issue, there is a black dot next to the M12 cable connector. This dot is aligned with the sensor tip and helps the user orient the probe as required.

Figure 3: Rheonics hygienic installation requirement for SRD.


[1]: http://www.ehedg.org/

[2]: https://www.3-a.org/

[3]: Rheonics EHEDG Installation Guideline