Electronic humidity sensors have experienced rapid development in recent decades, especially within the last 20 years. Before leaving the factory, manufacturers must calibrate their products using a standard humidity generator. The accuracy of modern electronic humidity sensors can typically reach 2% to 3% RH.
However, it's important to evaluate the accuracy of these sensors not just based on short-term performance but also on their long-term stability. In general, electronic humidity sensors do not perform as well as traditional dry-wet bulb hygrometers in terms of long-term reliability and service life. This is because they rely on semiconductor technology, which makes them sensitive to ambient temperature conditions. If the operating temperature exceeds the specified limits, the sensor may be damaged. Therefore, electronic humidity sensors are best suited for clean environments with normal temperature ranges.
Humidity measurement remains a challenging issue in metrology worldwide. What are the common errors that affect the accuracy of current electronic humidity sensors? Let’s take a closer look at the key factors:
First, sensor-related errors
One source of error comes from the sensitivity components. Variations in resistance and capacitance responses to humidity can lead to inconsistencies. Additionally, during signal conversion—when resistance or capacitance values are converted into voltage or current signals—errors can occur.
Temperature drift and time drift are also significant issues. Since humidity sensors are exposed to the gas being measured, they cannot be fully sealed like other electronic devices. This exposure makes them vulnerable to corrosion and contamination from acidic, alkaline, or organic compounds in the air. As a result, they tend to degrade over time and require periodic calibration. However, high-quality, long-life sensors can remain accurate for over ten years after proper calibration.
Second, errors introduced by secondary instruments
Signal processing in the secondary instrument can introduce distortion. For example, even after compensation at room temperature, a humidity sensor may still show inaccuracies at high temperatures due to its variable temperature coefficient.
Other factors include zero drift and temperature drift in the entire circuit, which can significantly impact measurement results.
Third, errors from the calibration process
Calibration equipment may not always be perfect. Issues such as an imperfect drying or saturation system, inaccurate pressure and temperature control in dual-pressure or dual-temperature methods, or improper mass flow meter operation in shunt methods can all introduce errors.
In the dew point method, leaks in the sampling line or excessively long tubing can cause temperature fluctuations, leading to large measurement errors. Insufficient balance time or heating elements near the sensitive parts can also interfere with the readings.
Finally, the position of the sensor in the testing environment can influence the results, as different locations may have varying humidity levels and environmental conditions.
Understanding these potential sources of error helps in improving the accuracy and reliability of electronic humidity sensors in real-world applications.
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