ISO 19685:2017

Overview - ISO 19685:2017 (Pirani gauges, calibration & uncertainties)

ISO 19685:2017 is an international standard for Pirani vacuum gauges used in vacuum technology. It defines the parameters, calibration procedures and the measurement uncertainties to be considered when operating Pirani gauges over the pressure range 0.01 Pa to 150 kPa. The standard complements general vacuum‑gauge guidance (ISO 3567 and ISO 27893) and provides additional procedures to characterize response time and hysteresis of Pirani gauges.

Key topics and technical requirements

• Scope and definitions

  • Applies to thermal‑conductivity type Pirani gauges (including convection‑enhanced variants noted in the standard).
  • Defines physical parameters such as internal volume, thermal accommodation coefficient, long‑term instability, response time (τ) and hysteresis.

• Specifications for gauge design and operation

  • Expected measurement range, full scale and output types (pressure, voltage or current).
  • Requirements for materials exposed to gas, connecting flange, interface/pin‑connections, warm‑up period, compatibility between gauge tube and controller, normal operating conditions, power supply, cable length, maximum bake‑out temperature, mounting orientation and dimensions.

• Optional (additional) specifications

  • Long‑term instability, relative sensitivity factor, hysteresis, response time, inspection record, configuration, weight, storage/transport conditions, photographs, maximum power consumption and set points.

• Calibration and measurement procedures

  • Conditions for calibration, assembly/adjustments of the calibration item, direct‑comparison calibration procedures, uncertainty evaluation during calibration, and content required in a calibration certificate.
  • Specific measurement procedures for determining hysteresis and response time.

• Measurement uncertainty

  • Guidance on evaluating measurement uncertainties both during calibration and at the point of use, following methods consistent with ISO 27893 and ISO 3567.

Practical applications and who uses ISO 19685:2017

• Who benefits

  • Calibration laboratories and metrology institutes performing traceable calibrations.
  • Manufacturers of Pirani gauges and vacuum gauge controllers.
  • Engineers and technicians responsible for vacuum systems in research labs and industrial vacuum processing.
  • Quality managers ensuring instrument performance and traceability.

• Practical uses

  • Establishing traceable calibration procedures for Pirani gauges.
  • Characterizing gauge dynamic behavior (response time, hysteresis) for process control.
  • Defining uncertainty budgets when Pirani gauges are used as reference or process monitors.
  • Ensuring compatibility and safe operating conditions (bake‑out, power, mounting) for reliable vacuum measurement.

Related standards

• ISO 3567 - Vacuum gauges: calibration by direct comparison with a reference gauge
• ISO 27893 - Evaluation of uncertainties for calibrations by direct comparison
• ISO/IEC 17025 - General requirements for competence of testing and calibration laboratories

Keywords: ISO 19685:2017, Pirani gauge, vacuum gauges, calibration, measurement uncertainties, vacuum technology, response time, hysteresis, thermal conductivity gauge, pressure range.