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Thermal Damping of Temperature Probes: Monitoring yes, Mapping no (maybe)
保罗·丹尼尔（Paul Daniel），瓦萨拉
Senior GxP Regulatory Compliance Expert
发布：
Feb 2, 2018
Industrial Measurements
Life Science
We receive a lot of questions on the use of thermal damping devices for temperature sensors. Mostly it depends on your application, but for mapping studies we usually advise against damping the measurements. This is because almost every controlled environment that needs to be qualified provides a stable environment for the stored item by bathing it in temperature-controlled air. The temperature of the stored item is dependent on the temperature of the air. The air temperature will fluctuate based on normal control cycles and the stored product temperature will fluctuate accordingly. The product temperature will fluctuate less because it will always havea higher specific heat than the air.因此，该产品将经历相对于空气温度减弱的温度波动。
But before we give our comments, there is a paper on research into thermal buffering methods in a paper published by NCSLI. They tested 20% concentrations in several aqueous media in different vial sizes, but found no significant differences.
Instead, their tests determined that the location of the probe inside the chambers had a larger impact. Meaning, whatever buffer you use for whatever probes you use, probe placement within a monitored space is crucial. Placing the buffered probe in the geometrical center of the monitored space will be usually be the most representative of the temperature of the space.
“优化数据记录器设置并用于冷藏疫苗温度监测”
Authors: Michal J. Chojnacky, Luis Chaves Santacruz, W Wyatt Miller, Gregory F. Strouse, NCSLI Measure: The Journal of Measurement Science, Vol. 10 No. 3, September 2015
Accessed: February 2, 2018
Accessed: February 2, 2018
温度Damping in Application
产品generally have a higher thermal mass than air. The actual air temperature represents the worst-case scenario. Product temperature (which we can think of as a damped signal) will always show less fluctuation than air. In mapping/validation applications we always want to address the worst-case scenario, so measuring the undamped air temperature is the right choice; both easy to defend, and easier to do.
但这提出了一个问题，即是否在任何情况下我们会削弱用于映射研究的探测。当我们测量空气温度时，当环境无法正确执行时，这是一个问题。发生这种情况时，通常是1）设备故障的症状，或2）不适合任务的设备。在这些情况下，采用绘制阻尼空气信号的做法只是隐藏了设备故障或设备不合适的基本问题。
However, when a validation expert says a damped air temperature just hides bad equipment, this rarely means that your customer will magically obtain a budget to buy new equipment. It's more likely that the customer will move forward with their plans to map with faulty equipment, and expect you (the validation expert) to find an appropriate solution. This can happen when validation is put at the end of the project, rather than the beginning.
无论出于何种原因，运行验证研究的人们都面临挑战。我们的建议是绘制空气中的裸传感器，未阻尼信号，以查看环境在将气温映射为最坏情况下时是否可以满足验收标准。即使您期望它将失败，也要这样做。一旦失败，您就有一个基本原理可以使用阻尼信号来支持，并且您将根据原始研究数据知道可能需要多少阻尼。
Let's say you have mapped an area and the data did not met acceptance criteria. Now you need to map again. Examine what will be stored in the environment. You don't want your artificial damping of the sensors to exceed the natural damping that the smallest items stored in the environment will experience. For instance, if the smallest item stored in the environment is 50ml vials of liquid product, then we would want to use a significantly smaller volume of placebo product (say 20ml vials of glycol) in which to place our sensors.
You get the idea… the mapping study will be compromised (read "meaningless") if the product stored is more sensitive to temperature than the sensors we are using to map the environment. And, when we are done with our mapping, procedural controls will be needed for that environment to make sure that no products smaller than 50ml are ever stored in the area.
因此，您可以潮湿的空气温度信号。但是，但是根据我们的经验，这通常只是掩盖了故障或不适当的设备。它可能会受到审计的问题。它将需要为映射环境进行持续的程序控制。
Now you may ask: Does this logic apply to constant monitoring after mapping has been completed and units are in use?
Yes, and no. Monitoring applications are a different story. Mapping studies show that a process performs reliably using challenge scenarios such as the worst-case examples. Monitoring is quality control to ensure the process is running correctly. But wait! There are some variables to consider…
通过监视，您理想地选择了从研究中得出的信息，选择传感器位置，通常是警报限制。为了使此过程具有一定的连续性，我们希望监视过程将遵循我们的映射过程。换句话说 - 如果我们开始抑制信号以监视，我们是否有合理的期望我们的数据可以比较？我们将以未在映射研究中使用的方式监视该过程，然后期望能够与数据进行比较。
但这通常是人们做的。
They just place a monitoring probe in the chamber, damp the signal with glycol or some solution, and don’t give it another thought. What will your auditor say? You have validated your chamber by mapping (well done!), so you are monitoring with a validated monitoring system, and even if the damped monitoring data isn’t comparable to your mapping, or proven to be equivalent to your typical load, at least it will capture catastrophic failures in your chamber – power loss, compressor failure, door left open, etc.
显然，我们支持监测空气温度的实践。监测空气温度的缺点是，温度变化速度更快，并且更容易对环境扰动（例如让室内门打开或添加不同温度的产物）响应。
However, these perturbations are things that represent a chamber that is not be properly managed.
有了训练有素的人员，门没有被遗忘或打开。通过适当的处理程序，在将其放置在我们的房间中之前，在适当的温度下进行了新的库存。但是，使用阻尼的监视信号 - 这些问题（通常是过程不良，训练无效和设备失败的指标）消失了。
问题不应该被隐藏，房间中未受阻尼的空气温度信号可以告诉您更多的信息，而不是冰箱的性能，它可以告诉您部门的性能。此外，有了适合其目的的高级监视系统，您可以使用警报延迟来实现与阻尼信号相同的效果，而不会失去数据敏感性。这是更好地利用技术来获取诚实数据并设置智能监控。
那么，阻尼信号的主要缺点和优势是什么？在正面：阻尼信号在操作中提供了简单性。您可以安装传感器并忘记。负面的一面：您可能会因高流量区域溢出的阻尼流体而陷入困境。而且您可能会在监视过程的逻辑上陷入混乱，因为数据并不能真正代表产品所经历的内容。您将失去评估偏差的能力，除非您知道您的阻尼信号仍然比产品更敏感。一种可能的解决方案是进行研究，以确保您的阻尼监视信号近似于您的产品。
We have seen some industries successfully damp monitoring signals, such as eye/cornea banks, where guidance specifies that the sensor be placed in 20ml of Optisol, as this is the recommended way to store a cornea. However, eye banks deal only in corneas, and all corneas are conservatively very similar.
在现场，我们看到大多数公司都会抑制监视信号，而实践并没有消失。只要我们继续进行映射研究，将连续监控放置在适当的位置，以确保数据中没有差距，并且会使您作为监视系统的组成部分感到震惊。总是，了解您的环境（映射）并了解产品和流程所需的温度很重要。
We are always happy to have your feedback and comments!
Thanks for your reply! I will hope you will allow me to disagree a little.
在我曾经绘制过的任何环境（也许是LN2 Dewar之外），我从未观察到稳定状态。试图执行校准时，很难实现稳定的环境。随着控制电路的加热或冷却空间，每个环境都会显示出一些可变性。
您的基本前提肯定是正确的，也就是说：如果环境（空气温度）在规范范围内，则该产品将在规范之内。但是相反的不正确 - 如果环境（空气温度）不具体规格，则不意味着该产品不超出规格
As an extreme example, I once mapped a refrigerator storing 1L bags of human blood with specifications of 1C to 10C. The air in the refrigerator varied widely, from -1C up to 13C. The product varied a little ranging from 4C to 5C. This was a clear example of the environment failing, without the product failing.
If I understand you, I think you are recommending to map both air temperature (for equipment qualification) and product temperature (for qualification of the monitoring process). And I agree with you that this is the most circumspect and risk-averse approach. From my own experience and from the questions I receive on how to map from our customers, most companies do not have the resources (time, equipment, expertise) to do both. They want to do the best they can with the resources at their disposal. Therefore, that has led us to recommend that if you can only map one of the conditions, you should map the air temperature, not the product temperature.
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最好的祝福，
保罗·丹尼尔（Paul Daniel）