Standard leak orifices and reference tanks for instrument calibration

1. Why They Are Needed

Over time, sensors, valves and tubing in any leak tester drift.
Periodic calibration with a certified standard leak (known leak rate Q) and a certified reference volume (known volume V) ensures traceability to national/international standards, detects out-of-tolerance conditions, and supplies correction factors for subsequent measurements.

2. Standard Leak (Leak Artifact)

• Definition
  A micro-flow element whose leak rate Q (at specified pressure & temperature) has been certified by a metrology institute.
  Common units: Pa·m³/s, sccm, mbar·L/min.
• Typical Designs
  – Capillary type: glass or metal capillary, stable for 10⁻³ ~ 10⁻⁷ Pa·m³/s.
  – Permeation type: helium diffuses through quartz; lower leak rates but temperature-sensitive (10⁻⁷ ~ 10⁻¹¹ Pa·m³/s).
  – Integral on/off valve: opened only during calibration to prevent contamination.
• Usage Notes
  – Recertify every 6–12 months.
  – Allow ≥30 min thermal stabilization before use.
  – Connect only clean, dry gas (N₂ or He).

3. Reference Volume (Master Volume)

• Definition
  A rigid, corrosion-resistant vessel whose internal volume V has been measured to within ±0.2 %. It is used to simulate the test part or to provide a “known volume” for instrument calibration.
• Key Features
  – Material: electropolished 304/316 L stainless steel.
  – Quick-connect or threaded port with an inlet filter.
  – Optional built-in temperature probe for real-time monitoring.
• Typical Uses
  – Zero calibration in differential-pressure instruments (acts as “zero-leak” reference).
  – Volume calibration method: combine known V and known Q to check instrument sensitivity.
  – Linearity test: switch among several certified leaks on the same V to verify full-scale linearity.

4. Example Calibration Sequence (Differential-Pressure Tester)

1. Warm-up tester 30 min.
2. Connect reference volume.
3. Set test pressure P.
4. Close standard-leak valve → perform zero calibration.
5. Open standard-leak valve.
6. Tester should display Q_certified (tolerance ±5 %).
7. If out of tolerance, enter correction factor K = Q_certified / Q_measured.
8. Repeat steps 4–7 until error ≤ ±2 %.
9. Print or save calibration record.

5. Maintenance & Storage

• Standard leak: store in a clean, dry box; avoid drops and oil.
• Reference volume: recheck volume every two years for corrosion or dents.
• Calibration interval: production line—weekly; laboratory—monthly.
• Records: retain ≥3 years to comply with ISO 9001, IATF 16949 traceability.

In one sentence
“The standard leak gives you a ‘known leak,’ and the reference volume gives you a ‘known volume’; together they lock the tester’s readings to a traceable accuracy.”