Sterilization tunnels are critical in pharmaceutical manufacturing to ensure ampoules are sterilized effectively and consistently. Accurate temperature calibration ensures compliance, product safety, and process reliability.
1. How to Calibrate Temperature Sensors
Remove sensor (if possible) or isolate for in-situ calibration .
Use a calibrated reference thermometer (traceable to NABL/NIST).
Insert both the reference probe and sensor under test into a dry block calibrator or liquid bath .
Test at 3–5 temperature points (100°C–300°C).
Allow thermal stabilization (~5–10 min per point).
Record readings & calculate Deviation = Sensor Reading − Reference .
Pass if deviation ≤ limits, else adjust or replace .
Document calibration: date, person, instrument ID, certificate no.
2. Calibration Limits / Acceptance Criteria
Parameter Typical Limit in Tunnel Temperature Accuracy ±0.5°C to ±1.0°C Resolution 0.1°C or better Repeatability ±0.2°C Stability ≤0.2°C drift / 24 hrs Calibration Sensitivity ±0.1°C (ideal) Uniformity (validation) ≤ ±15°C across sensors Calibration Frequency Every 6–12 months / SOP
3. Which Temperature Sensor to Use
Application Sensor Type Why Used Accuracy / Resolution Tunnel air monitoring Pt100 RTD (Class A) High accuracy, low drift ±0.15°C / 0.1°C Load temp mapping Fine-wire Type K TC Fast response, flexible ±0.5°C / 0.2°C Ampoule surface Type T / K TC Glass contact ±0.5°C High-temp zones Type K / N TC Oxidation resistance ±1.1°C Reference standard High-accuracy PRT Calibration reference ±0.03°C Controller input Pt100 RTD (A/B) Process loop ±0.15°C (A) / ±0.3°C (B) Safety sensor TC (K/N) or RTD Cut-off protection ±1°C
4. Sensor Characteristics
Sensor Range Accuracy Resolution Sensitivity Pt100 RTD (Class A) -200 to +650°C ±(0.15+0.002×T) 0.01–0.1°C High Pt100 RTD (Class B) -200 to +650°C ±(0.30+0.005×T) 0.1°C Medium Type K TC -200 to +1250°C ±2.2°C 0.2–0.5°C Fast, lower accuracy Type T TC -200 to +350°C ±1°C 0.1°C Medium Type N TC -200 to +1300°C ±1.5°C 0.2°C Good for high-temp High-Accuracy PRT 0 to +500°C ±0.03°C 0.01°C Excellent
5. Recommended Calibration Equipment
Equipment Purpose Accuracy Dry Block Calibrator Stable heat source ±0.1–0.3°C Liquid Calibration Bath High-accuracy calibration ±0.01°C Reference PRT Comparison standard ±0.03°C Calibrated Thermometer Field checks ±0.1–0.2°C Data Logger Temperature mapping 0.1–0.5°C Multimeter (TC input) Reads TC output ±0.05% of reading
6. Summary Matrix
Application Sensor Interval Accuracy Production control Pt100 RTD (A/B) 6–12 months ±0.5°C Validation mapping Type K/T/N TC Before each study ±1°C Reference calibration High-accuracy PRT 1 year ±0.05°C Glass surface Type T / Fine K Case-by-case ±1°C Safety sensor TC / RTD Annually ±1.5°C
✅ Best Practices
Use Class A RTDs / Special Limit TCs for critical control points.
Trace all calibrations to NABL / NIST standards .
Maintain certificates & logbooks .
Replace thermocouples showing drift or damage.
Use shielded fine-wire TCs for vial mapping (avoid metal contact).
📚 Guidelines & References
WHO TRS 961 Annex 6 – Good Manufacturing Practices for sterile products.USP <1223> – Validation of Alternative Microbiological Methods.USP <1058> – Analytical Instrument Qualification.FDA Guidance – Sterile Drug Products produced by aseptic processing.ISPE Baseline Guide Vol 3 – Sterile Manufacturing Facilities.EMA Annex 1 (2022) – Manufacture of Sterile Medicinal Products.NABL / NIST – Calibration traceability standards.
With structured calibration and adherence to regulatory guidelines, pharma companies ensure compliance, safety, and product consistency.
