EKS-HUM-027 / Condensation, measurement and control
Hygrometer
湿度计
A hygrometer is an instrument that measures a defined humidity quantity in a gas, such as RH, dew or frost point, water amount fraction or water mass ratio.
- Aliases
- humidity meter, humidity-measuring instrument
QUANTITY, SYMBOL AND UNIT
Quantity / objectHumidity-measuring instrument
UnitNot applicable
Definition
A hygrometer is an instrument that measures a defined humidity quantity in a gas, such as RH, dew or frost point, water amount fraction or water mass ratio.
The name describes an instrument category, not one universal sensing principle. Capacitive RH sensors, chilled-mirror instruments and other methods have different measurands, response times, contamination sensitivity, calibration needs and operating ranges.
Relations and distinctions
Hygrometer and humidistat
A hygrometer provides a humidity measurement. A humidistat uses a humidity input to perform a control action and may not provide metrology-grade measurement.
RH meter and dew-point hygrometer
They measure different humidity quantities; conversion requires temperature, pressure and the relevant psychrometric model.
Engineering meaning
- Select the instrument by measurand, range, uncertainty, response, contamination exposure and installation location.
- Keep calibration records and verify the complete sampling path where low dew point or process gas is measured.
Common misconceptions
MisconceptionAll hygrometers measure RH directly and can be compared by one accuracy number.
Accurate explanationHygrometers can measure different quantities with different principles, units, ranges and uncertainty statements.
Application boundaries
- A calibration certificate does not remove installation, response-time, drift or contamination effects in service.
- One sensor location may not represent spatial gradients or hidden enclosure conditions.
Supporting sources
-
National Institute of Standards and Technology / SRC-NIST-HYGROMETERS
Hygrometers ↗
Updated 2022-11-28 / Calibration scope, instrument types and humidity measurands
Supports: Hygrometers are instruments used to measure humidity quantities; Possible measurands include dew/frost point, RH, water amount fraction and water mass ratio; Different instrument types require measurand-specific calibration -
National Institute of Standards and Technology / SRC-NIST-HUMIDITY-CAL
Humidity Calibration Services at NIST ↗
Updated 2025-08-14 / Description and calibration-uncertainty sections
Supports: Humidity instruments are calibrated against humidified air of known moisture content; Calibration uncertainty depends on the humidity quantity and conditions -
ASHRAE / SRC-ASHRAE-41-6-2021-A
ANSI/ASHRAE Addendum a to ANSI/ASHRAE Standard 41.6-2021 - Standard Methods for Humidity Measurement ↗
Addendum a, 2022 / Public addendum and scope
Supports: Humidity measurement requires a specified method and operating conditions
Maintenance record
Hygrometer
- Maintained by
- Yakeclimate Engineering Team
- Authoritative sources verified
- August 3, 2026
- Terminology checked
- August 3, 2026
- Last updated
- August 3, 2026