In industrial production and scientific research, we often hear the term ‘dew point.’ But what exactly is dew point? Why do we need to measure it? And how should we choose the right dew point measurement instrument? Today, we will discuss this topic and conduct an in-depth comparison of two mainstream dew point measurement technologies: capacitance dew point meters and chilled mirror dew point meters.
What is dew point?
Dew point, simply put, is the temperature at which air cools to saturation under conditions where water vapour content and air pressure remain unchanged. When the air temperature drops below the dew point, water vapour condenses into liquid water, forming dewdrops or frost. Therefore, dew point directly reflects the amount of water vapour in the air and is an important indicator of air humidity.
Why measure dew point?
Industrial production: In many industrial processes, such as compressed air drying, electronic equipment manufacturing, and food processing, controlling the dew point prevents products from becoming damp, corroded, or damaged, ensuring product quality and production safety. Weather observation: Dew point data is crucial for predicting weather changes, assessing atmospheric stability, and evaluating visibility. Energy sector: In the storage and transportation of energy sources such as natural gas and liquefied petroleum gas, dew point monitoring prevents water vapour condensation from causing pipeline blockages or equipment damage. Scientific research: In fields such as materials science and chemical analysis, precise control of dew point conditions is critical to experimental success.
Capacitance method vs. chilled mirror method
PART-01 Principal Differences
The capacitance-resistance dew point meter is based on the principle of polymer thin-film capacitors. It measures dew point temperature by detecting changes in capacitance caused by the adsorption of water molecules by hygroscopic materials such as aluminium oxide. The core component is a capacitance sensor, which utilises the hygroscopic properties of the material to convert humidity into capacitance. The cold mirror method dew point meter measures dew point temperature using physical optical methods. When gas flows over a cooled mirror surface, condensation forms when the mirror temperature drops to the dew point. An optical sensor detects changes in reflected light to determine the dew point. This method relies on optical detection technology to directly reflect the condensation state of water vapour in the gas.
PART-02 Performance Comparison
Accuracy and Stability Cold Mirror Type: Higher accuracy (±0.1°C) and excellent stability, suitable for high-precision applications. Capacitive: Relatively lower accuracy (±2–3°C), affected by material ageing, requiring regular calibration for long-term stability.
Response Speed Capacitive: Fast response speed (90% response within 1 minute), suitable for rapid measurement. Cold Mirror: Slower response (takes several seconds to several minutes), limited by the efficiency of the cooling system.
Maintenance Costs: Capacitive method: Sensors are prone to ageing and require regular replacement (calibration cycle of 3–6 months), resulting in higher maintenance costs. Cold mirror method: The mirror surface requires regular cleaning, but the core components have a long service life, resulting in lower long-term maintenance costs.
PART-03 Application scenarios
The capacitive dew point meter is suitable for: on-site rapid testing, portable applications, and continuous monitoring of industrial processes (such as compressed air drying and glove box humidity control)—advantages: Fast response, compact size, suitable for dynamic environments. Cold mirror-type dew point meters are suitable for: Laboratory high-precision measurements, standard transfer, monitoring of insulating gases in power equipment (e.g., SF6 gas), meteorological observations—advantages: High accuracy, strong stability, suitable for static or low-flow environments.
Instrument sharing
TP205 Capacitance dew point meter
Application Scenarios: Suitable for moisture detection in dry gases. The gases tested include: H2, SF6, N2, O2, Ar2, CO2, compressed air, and other gases. It is widely used in industries such as power, chemicals, aviation, metallurgy, pharmaceuticals, and food.
Features: ① Advanced probe protection function, resistant to contamination and interference. ② Automatic calibration programme ensures long-term stability of the instrument, overcoming almost all unfavourable factors in field measurements. ③ Real-time storage and printing of measurement data. ④ Large-sized true-colour touchscreen. ⑤ Unique large-capacity storage function, with digital power display. ⑥ Simple operation and convenient portability. interference-resistant, high repeatability, fast response speed, high sensitivity, and excellent stability. ⑦ Optional RS232/485 signal output.
TP208 Chilled Mirror Dew Point Meter
Applicable scenarios: Designed and manufactured in accordance with the requirements specified in GB/T 5832.2-2016 ‘Determination of Trace Moisture in Gases – Part 2: Dew Point Method’, GB/T 11605-2005 ‘Methods for Measuring Humidity’, GB/T 17283-2014 ‘Determination of Water Dew Point in Natural Gas – Cooling Mirror Condensation Hygrometer Method’, DL/T 846.5-2004 ‘General Technical Requirements for High-Voltage Testing Equipment—Part 5: Sulphur Hexafluoride Trace Moisture Analyzer,’ among others. It is widely used in fields such as meteorology, power, metallurgy, petrochemicals, electronics, textiles, pharmaceuticals, food, air conditioning, and aerospace for measuring the dew point of gases such as nitrogen, sulphur hexafluoride, and natural gas.
Functional Features: ① High measurement accuracy with a resolution of 0.01°C and optimal measurement repeatability of 0.1°C. ② Utilises four-stage refrigeration technology with strong cooling capacity, capable of reaching -60°C. ③ Features an LCD display that shows dew point temperature, ul/L values, equilibrium process curves, gas flow rate, and other parameters. Convenient operation: ④ Features intelligent judgment and fault self-diagnosis alert functions, such as gas flow mismatch, low light energy, and unbalanced measurement result alarms. ⑤ Uses Peltier cooling with air-cooled heat dissipation, compact in size. ⑥ Uses corrosion-resistant tubing, capable of measuring corrosive gases. ⑦ Utilises digital fuzzy control technology, with short balancing stabilisation time, requiring only 3–5 minutes for measurement.
Conclusion
Selecting the appropriate dew point measurement instrument is not only critical for the accuracy of measurement results, but also directly impacts production efficiency, product quality, and experimental safety. Whether it is a capacitive dew point meter or a cold mirror dew point meter, each has its unique advantages and applicable scenarios. We hope today’s sharing will help you better understand dew point measurement technology and select the most suitable dew point measurement instrument for your industry!
