Humidity and Dew Point Sensors – Is Periodic Recalibration Necessary, and If So, How Often is Recalibration Required?
A common question customers ask is whether a humidity or dew point sensor requires periodic recalibration. The answer depends on the specific accuracy requirements of the process in which the sensor is used. Most sensors will drift over time from their original specified accuracy, so periodic verification and adjustment may be required to restore them to their original accuracy specifications. This process is referred to as calibration or, more accurately, recalibration since most sensors are initially calibrated during manufacturing.
Recalibration is particularly relevant for humidity and dew point sensors because their sensing elements are directly exposed to the environment. Beyond normal electronic drift, environmental contaminants may affect sensor performance. If accuracy is a concern, as it is for most applications, the follow-up question is: How often is recalibration required? A general rule of thumb is that recalibration should be performed every 12 to 24 months. However, a more precise answer depends on several factors, including:
-
Organization/Industry Policies
-
Process Requirements
-
Measurement Environment
-
Type of Sensor
Organization/Industry Policies
Certain industries regulate how often a sensor needs recalibration. For example, the pharmaceutical industry generally has more stringent recalibration schedules. Additionally, individual companies may establish their own recalibration requirements based on internal quality standards.
Process Requirements
Applications that are not highly dependent on measurement accuracy may tolerate longer intervals between recalibrations. Conversely, processes that require high precision may necessitate more frequent recalibration.
Measurement Environment
Environments containing contaminants have a greater impact on sensor performance than clean environments. Contaminants may include particulates or non-compatible gases. Most moisture sensors are designed to operate in air or inert gas environments, so exposure to other gases can negatively affect performance. Contaminants can alter the recalibration cycle or even damage the sensor.
Type of Sensor
The two most common types of gas moisture sensors are chilled mirror and capacitive sensors:
-
Chilled Mirror Sensors: These sensors use a mirror that is cooled until condensation forms on its surface. If exposed to contaminants, the mirror can be cleaned, potentially extending the recalibration interval.
-
Capacitive Sensors: These sensors contain an element that changes capacitance with moisture absorption. The capacitance is then used to determine humidity. If a capacitive sensor becomes contaminated, it may require recalibration or even replacement.
Alternatives to Recalibration
Some organizations have in-house calibration labs, but most companies must send sensors to the manufacturer or an external calibration lab. Recalibrating humidity sensors requires specialized equipment, such as an environmental chamber and/or reference gas. Additionally, the process can be time-consuming and costly, particularly if multiple calibration points are needed. In cases where recalibration costs are prohibitive, alternative solutions include:
-
Replacing the Entire Sensor: For low-cost sensors, replacement may be the most cost-effective option.
-
Replacing the Sensing Element: Some humidity devices feature field-replaceable sensing elements that come pre-calibrated, making replacement a convenient solution.
-
Verifying Sensor Accuracy with a Secondary Device: Organizations with multiple sensors can maintain a regularly recalibrated reference sensor. This reference sensor can be used to verify the accuracy of other sensors, ensuring recalibration is performed only when necessary.
By understanding these factors and alternatives, organizations can make informed decisions about sensor recalibration to ensure optimal performance while managing costs effectively.
Check out IOThrify's lineup of humidity and dew point instruments.