Dew point

Dew point temperature

The drier the condition, the more challenging it is to measure
Vaisala keeps pushing the boundaries of measuring humidity lower and drier

Dew point: a critical parameter in industrial manufacturing

In many industrial manufacturing processes, precise control of humidity, or trace moisture, is essential to maintain product quality, ensure equipment reliability, and support safe and efficient operations.

Low-humidity environments, defined here as <10 %rh, require measurement technologies that remain accurate and responsive under demanding conditions.

Dew point, the temperature at which water vapor begins to condense, is the benchmark of process dryness as it is a direct indicator of the absolute moisture content in air or gas.

Unlike relative humidity, which depends on temperature, dew point remains consistent and provides a stable metric for dry environments and critical processes.

Vaisala provides compact dew point probes that deliver accurate, stable, and fast-responding measurements.

Their rapid response enables the timely detection of moisture changes, helping operators maintain control of trace moisture-sensitive processes, minimize contamination risk, and avoid unplanned downtime or system failures.

How dew point is measured

Dew point is measured by determining the moisture content of air or gas and converting it to the temperature at which condensation begins.

Vaisala dew point/frost point measurement is based on revolutionary capacitive thin-film humidity technology, sensing relative humidity and ultra-stable platinum-based temperature sensors to determine dew point/frost point calculated from these measurements.

Key factors that affect measurement quality

There are different measurement principles available, such as advanced humidity sensors that infer dew point from relative humidity and temperature, and chilled mirror instruments that observe condensation.

Accurate dew point measurement depends on:

• Temperature
• Pressure
• Contaminants and condensation
• Sensor placement and response time

Technology comparison

Review how Vaisala's dew point probe compares to CRDS' (Cavity Ring-Down Spectrometer)
and Chilled mirror transmitters in the most demanding operating environments, such as
rechargeable battery and semiconductor manufacturing.

Vaisala’s dew point probeCRDSChilled mirror transmitterTd measurement
range*-80 °C…+20 °C-100 °C…-50 °C -70 °C…+20 °C In-situ measurementYesNo, requires sampling and a large pressure differenceNo, requires samplingTd accuracy in
laboratory conditions* +/-2 °C+/-0.2 °C+/-0.2 °CPressure range* 1…50 bar 1…5 bar~ 1 bar onlyDependency of
atmospheric
conditionsNot dependentDependent. Stable atmospheric conditions required. Sampling might generate errors in non-laboratory
environment. Dependent. Minimum dew point will raise if the ambient temperature increases. Sampling might generate errors in non-laboratory environment.Response time* MinutesTens of minutesHoursSensitivityHighLow (cannot detect quick changes, averaging measurement)Low (cannot detect quick changes, averaging
measurement)Size Small and light. Fits easily to multiple locations Mid size, about 10 kgFrom big and heavy to mid sizeOperator to provide
regular serviceNot requiredNot requiredRequiredComponents requiring
serviceNot requiredNot required, if in clean environmentRequired (e.g., Peltier)Local calibration/
support availableYesUnlikelyUnlikelyDependency of
background gasesMinorPotentially strongPotentially crucial

* Typical values in battery and semiconductor manufacturing

Common measurement challenges and how to avoid them

Probe installation position

It's particularly important to:

• Ensure the sensor sees representative gas conditions
• Use proper materials and tightness to avoid leaks
• Consider accessibility for validation needs

Understanding dew point dynamics

It's particularly important to:

• Remember that increased pressure increases the dew point
• Account for the pressure influence on dew point readings

Choosing the right measurement solution

It's particularly important to:

• Select technology appropriate for your environmental conditions
• Differentiate between the output range and the validated measurement ranges

FAQ

Can you measure -20…100 °C Td/f range

In theory yes, but it is impractical and expensive. Vaisala's instruments are optimized for certain dew point levels, and the selection covers a variety of instruments.

Is a sensor that can measure lower dew points a better sensor?

Not always. If you need accurate measurements at extremely low dew points, then yes, a lower-range sensor is beneficial. But for moderately dry conditions like -40…-60 °C Td/f, choosing an instrument that goes down to -80 °C Td/f will not improve performance.

The best sensor is the one that matches your process, not the one that measures the driest possible conditions.

Does my sensor lose accuracy if exposed to ambient humidity levels or even condensation?

It depends on the sensor technology. Vaisala DRYCAP sensors do not lose accuracy when stored in typical indoor humidity, and they can even be exposed to liquid water and still recover fully.

When do I need a sampling system?

A sampling system is relevant when one or more of the following apply:

• The gas temperature exceeds the sensor's tolerance
• The process pressure is higher than the sensor's tolerance
• Chemicals or particles cannot be pre-filtered and would cause harm to the sensor
• The installation location does not permit a direct sensor mounting
• The instrument must be removed regularly while the process is running

Applications where dew point measurements are critical

Measuring dew point allows for predictive maintenance, process optimization, and regulatory compliance across many sectors

Beneficial for all applications requiring low dew point levels

• Unique research projects
• Aerospace and defense
• Specialized sensors
• Critical compressed air lines
• Critical, high-purity gases: air, nitrogen, argon, helium, and other inert gas lines
• Glove boxes and isolators
• Pharmaceutical manufacturing, including certain Active Pharmaceutical Ingredients and lithium-based medical devices
• Sensitive chemicals, catalysts, or metal powders or other components that might oxidize or hydrate when moisture is present
• Display manufacturing
• Optical coating and laser laboratories