Test & measurement
WHY SHOULD DEW POINT SENSORS HAVE A FAST RESPONSE?
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umidity control is obviously critical to ensuring battery quality and preventing defects. Battery manufac- turers use dehumidifier units (DHU) to ensure that the air circulating in the process meets strict specifica-
tions. In battery production, humidity levels need to be kept extremely low, which means that a lot of dry air is needed, and drying requires heat and, therefore, energy. One of the most important ways to optimise energy usage is to measure dew point and tempera- ture and use these parameters to control the DHU. The amount of heating required changes as the outside humidity changes. On wet days more heat is needed and on dry days less, but the air fed into the manufacturing spaces must be consistently dry. So how can the dryness of the air blown in by the DHUs be kept at exactly the right level without wasting energy?
ACCURACY AND SPEED ARE ESSENTIAL
In battery manufacturing the sensors used to measure humidity must be extremely accurate: At a dew point of around -70 °C, there will only be 2.6 molecules of water in a million particles of air.
Speed is also of the essence. The rotating drums inside DHUs consist of two main parts:
the drying section made of desiccant material that draws the moisture out of the air
the regeneration section that drives heated air in the opposite direction to take moisture away from the desiccant material
The segments typically rotate once every ten minutes or so. If the moisture level of the incoming air is above
By Antti Viitane, product manager at Vaisala
the set limit, more heat is needed to remove the water molecules; if the moisture level is below the set limit, less heat is needed. The sensor technology must be able measure the changes in humidity within the ten-minute window or the opportunity to adjust the heating for that rotation will have been missed. To get around this challenge, sensors that are too slow to detect such changes in time typically average out results across multiple readings. The problem with this approach is that drying cannot be controlled in real time. Lack of control over drying leads to unstable humidity condi- tions, increased safety risks, and potential negative impacts on product quality.
FAST RESPONSE TIME ENABLES REAL-TIME CONTROL
The ability to measure humidity variations within one drum rotation, and not just between rotations, is a vitally important feature of dew point sensors in battery manufacture. With this capability it is possible to control the process in real-time to maintain optimal dryness levels in each stage of production and to prevent product defects. Sensor response times are slower when air is dryer, and faster at higher humidity levels. The extreme dryness required in the DHUs of battery plants makes
January 2025 Instrumentation Monthly
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