Placing Sensors Outside the Warehouse - Is it needed? Plus: How to reduce the total number of sensors in Validation/Mapping

Piritta Maunu
Life Science Regulatory Compliance and Industry Expert​
Industrial Measurements
Life Science

In this week's blog, we feature two questions our regulatory expert Piritta Maunu received on environmental qualification. Piritta describes why placing an external sensor outside storage areas is important, and outlines a method for reducing the number of sensors in thermal validation of large spaces. 

Piritta writes:

Dear C,Thank you for joining our webinar and thank you for emailing me your excellent question:
"Do you suggest also locating a mapping sensor external to the warehouse i.e. outside to assess the challenge during the study?"
Yes, we definitely suggest to locate one sensor at ambient conditions outside the warehouse. This is really important, as you already seem to understand, in case you have some fluctuating mapping results or even out of specification (OOS) mapping results inside the warehouse. When you have one sensor outside the warehouse you are able to understand a bit more of the "big picture" of your warehouse.

  • That externally located sensor can answer these questions (among others):
  • How different ambient environmental conditions affect your mapping results?
  • How should you plan your product storage areas inside the warehouse?
  • Do you need some preventive actions related to your processes to overcome some extreme ambient conditions?

I hope my answer is helpful and if you have further questions, please don't hesitate to contact me again.

Best Regards,
Piritta Maunu


Reducing Sensors in Mapping Studies - Two Methods

Dear A, Thank you for joining our webinar and forwarding your question: "Please repeat how you reduce sensor quantity?" Usually, when we talk about warehouses we mean large areas. So in mapping an area ≥ 20 m3, reducing sensor density can save a significant amount of money and effort.



There are a couple approaches to reducing the number of sensors. You could do it by mapping only the locations where the product is stored (shelves, racks). Or… by using in the three-dimensional (3D) area stacks of three sensors - but in practice, you remove every other sensor. From a presentation my colleague Paul Daniel gives on this method, please see the following three images:

  • Note1: The balls represent the sensor locations.
  • Note 2: Faint balls represent the sensor locations that can be removed.
  • Note 3: On the right hand side you see the amount of sensors before and after the reduction.






The maximum distance between the "stacks of three" shouldn't be more than 15-25 meters (RT, room temperature) or 5-8 meters in cold storage areas (+2…+8˚C).

Hope that this answer is helpful








Paul Daniel, Vaisala

Senior GxP Regulatory Compliance Expert

Paul Daniel has worked in the GMP-regulated industries for over 25 years helping manufacturers apply good manufacturing practices in a wide range of qualification projects.  His specialties include mapping, monitoring, and computerized systems.  At Vaisala, Paul oversees and guides the validation program for the Vaisala viewLinc environmental monitoring system.  He serves as a customer advocate to ensure the viewLinc environmental monitoring system matches the demanding requirements of life science and regulated applications.  Paul is a graduate of University of California, Berkeley, with a bachelor’s degree in biology.

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