What the Regulations say about Redundant Sensors in GxP Environments

Piritta Maunu
Piritta Maunu
Life Science Regulatory Compliance and Industry Expert​
Published: Jun 22, 2018
Industrial Measurements
Life Science
We recently received this question by email:

Do I need separate instruments for monitoring and controlling critical parameters in a WFI system.
If YES where can I find that in FDA CFR or Eudralex?
If NO where can I find that in FDA CFR or Eudralex?

Vaisala Life Science Industry Expert Piritta Maunu wrote in reply:

This is an excellent question and you are not alone in having asked.

In practice, Eudralex EU GMP Volume 4 or FDA Code of Federal Regulations Title 21 regulations rarely give exact rules for questions relating to parameters or specific technologies.  So the short answer is – no, you probably won’t find a specific regulation regarding adding separate, autonomous instruments.

However, if we can’t find clear guidance in the regulations, we should evaluate the issue based on the risk management principles that both EU GMP and cGMP strongly advocate. In the case of instrumentation for a WFI (water for injection) system, we can conclude that this is a critical system because it’s key to a process that will be focused on during an inspection.

There are two other criteria that help define us this system as critical:
• Issues with this system might impact patient safety.
• Issues with this system could harm your company’s reputation, or cause extra work if the system is cited as problematic during an inspection.

In both scenarios, the risk is unacceptably high.
So best practice is to evaluate the risks related to system malfunction according to risk management principles.

Probability x Severity of Impact = Level of Risk

And the more risk inherent to a system, the more attention we pay to the system in terms of preventive maintenance, planning, validation and documentation.

This leads us to risk mitigation actions for any systems we evaluate as critical.

One fairly simple solution to mitigate risks like this is to add redundant sensors. Two separate sensors rarely fail or drift exactly the same way at the same time. Specific to WFI systems,one approach to is use a separate controlling and monitoring sensor. This simple redundant sensor approach gives us ability to compare sensor results and to react earlier to possible problems.


However, in my opinion this is why we often get different answers (yes and no) to this type of question. Some companies mitigate risks by using redundant sensors. Some companies mitigate risks with other solutions like following other internal procedures such as daily or weekly equipment/sensor checking activities.

Whatever you do, your decisions should be based on the principles of risk assessment. 

Interestingly, I had the same discussion in R3 Nordic Symposium and Exhibition, in Naatali, Finland in May 2018. In that conference several different cleanroom area manufacturers and validation experts agreed that it's a current good practice in cleanrooms and with critical equipment (like sterilizers, autoclaves, depyrogenation equipment, etc.) to use redundant sensors.  You can also use handhelds for scheduled spot checking sensors that are integrated to equipment, or a secondary fixed sensor that is calibrated regularly; that will serve as your redundant sensor and ensure that any associated problem is immediately identified before quality is at risk.

While there is no regulatory guidance recommending redundant sensors, this is a common practice derived of quality risk management principles for critical processes and equipment. From our industry contacts we’ve seen that the practice is becoming more common in many GxP-regulated applications.

I hope you find this answer useful. Please find some links below to more training materials on Risk Assessment for GxP environmental management. A useful document is the ISPE’s GAMP 5 “A Risk-based Approach to Compliant GxP Computerized Systems.”


Best Regards,
Industry Expert, Life Science
Vaisala Industrial Measurements, Products and Systems (R&D and technology development)

More Information on Performing Risk Assessments:

In this 1-hour webinar, Senior Regulatory Expert Paul Daniel walks you through risk assessment techniques such as the Risk Scoring Rubric.

Webinar & Presentation Slides

Calibration Risk Assessment: Where to Start (includes Vaisala's Calibration Guide)

More reading on GxP Environmental Management Best Practices:


Piritta Maunu
Liftup: Contact Card | Jul 18, 2017

Piritta Maunu

Life Science Regulatory Compliance and Industry Expert​

Piritta Maunu has 15 years of experience in biotechnology, having worked in several quality management positions. Maunu holds a degree of M.Sc. (Cell Biology) and is certified to teach with a specialty in General Biology, both degrees from the University of Jyväskylä, Finland. In her role at Vaisala, she supports the sales department, assists the quality department with audits, creates educational content for life science customers, and provides application support to R&D teams creating solutions for monitoring critical environments.


More Questions and Answers on Redundant Sensors

We received this question by email:


I attended one of your seminars on Continuous Monitoring Systems and we use many Vaisala Temp/RH devices. These devices are currently connected to our Continuous Monitoring System - viewLinc. However, we also have a Building Management System that has less robust sensors.

The question I have is twofold:

  1. Can the Vaisala devices communicate with both our systems - CMS and BMS?
  2. What is the industry practice concerning BMS and CMS sensors? Can both systems use the same sensor or do you need to have redundant sensors for the two different systems? I ask because, although our Quality Management goals are high, redundant sensors double the cost in installation, calibration, and purchase and we need to manage costs... Your input is greatly appreciated!

Thanks for your answers!

Can the Vaisala devices communicate with both our systems - CMS and BMS?

First off, thank you for attending our seminar!

Certain Vaisala devices can communicate with multiple systems simultaneously. However, if you want to communicate with a Vaisala continuous monitoring system and a non-Vaisala system, such as a Building Management System (BMS), then you must use Vaisala DL-series Data Loggers.

These data loggers can communicate with multiple systems via an OPC query. If your sensors are not Vaisala sensors, they can still interface with our system via a Universal Input DL4000 data logger, which will then allow communication with both a Vaisala CMS and your non-Vaisala BMS via OPC.

One of our application engineers can give you details on how this would work in your application. Contact us.


What is the industry practice concerning BMS and CMS sensors? Can both systems use the same sensor or do you need to have redundant sensors for the two different systems?

Regarding industry practice, there is no standard for using two redundant sensors, or for using one sensor to communicate data with two separate systems. However in our experience, we have seen both approaches work, so you can do it safely from a GMP perspective.

We recommend that you apply GMP level controls as your would for your monitoring system, rather than defaulting to BMS level controls (that are not generally GMP-compliant). Note that we are not talking about electronic controls, but rather of quality procedures to "control" the system to GMP standards.


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Sep 17, 2018

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