Hygrometer Calibration: Turnaround Times, On-Site Services & How It Works
Tra-Cal Lab has provided ISO/IEC 17025 accredited, NIST-traceable hygrometer calibration for over 35 years — trusted by NASA, the U.S. military, and NIST. We service every major brand, from Omega and Extech to Dickson, Vaisala and Fluke, with faster turnaround and lower cost than the OEM. We offer expedited services, on-site calibrationand Mid-Atlantic pickup and delivery to keep your operation running. Every certificate includes as-found/as-left data, so your measurements stand up to any audit.
Key Summary
Hygrometer calibration compares indicated relative humidity against a NIST-traceable reference hygrometer or chilled-mirror standard inside a stable humidity generator at multiple set points, and verifies the temperature channel at the same time, since RH readings are only meaningful alongside a correct temperature, with results documented on a calibration certificate. Standard turnaround is 3-5 business days with overnight rush available, and most hygrometers should be calibrated every 12 months by an ISO/IEC 17025 accredited lab.
Why Choose Tra-Cal?
ISO/IEC 17025 Accredited
Our lab is independently audited every year by ANAB to the industry's most rigorous quality standard, so every calibration is audit-proof.
Overnight Rush Available
When downtime isn't an option, expedited service gets your instrument calibrated and back in your hands overnight or within three days.
NIST-Traceable
Every measurement we make traces directly back to national standards, giving your results documented accuracy you can defend.
Trusted by NASA, the U.S. Military, and NIST
The organizations with the most demanding measurement requirements in the country choose Tra-Cal — yours can too.
Hygrometer Calibration Turnaround
| Service | Turnaround |
|---|---|
| On-site Calibration Service | Same-Day |
| Standard calibration with certificate | 3-5 business days |
| ISO/IEC 17025 accredited calibration | 4-6 business days |
| Expedited / rush | Overnight to 3 days |
Hygrometer Brands & Models We Calibrate
| Manufacturer | Popular Models We Calibrate |
|---|---|
| Extech | 445580, 445815, RH520, SD500 |
| Dickson | FH325, TH803, TH8-7C, TM320 |
| Omega | ITHX-W3, OM-73, RH411 |
| Vaisala | HM34F |
| Fluke | 971 |
Don’t see your model?
We support over 100 test equipment manufacturers — contact us and we’ll confirm coverage for your exact instrument.
Equipment & Standards Required
We maintain the following equipment and conditions required to calibrate a hygrometer accurately:
NIST-traceable chilled-mirror hygrometer or reference humidity standard with at least a 4:1 test accuracy ratio
Two-pressure or divided-flow humidity generator with documented chamber stability and uniformity
Calibrated reference thermometer for the co-located temperature measurement
Manufacturer’s calibration procedure and published RH and temperature accuracy specifications
Stable environment: controlled ambient temperature and a documented chamber soak time, with NIST-traceable reference standards and a documentation system
How to Calibrate a Hygrometer: Step-by-Step
Step 1: Inspect the sensor and allow a full chamber soak. Check the sensor filter or cap for contamination, confirm the probe and cable are undamaged, and allow the instrument to soak in the chamber until both RH and temperature readings are fully stable — humidity sensors are slow and rushing this step is the most common error.
Step 2: Perform “as found” verification. Record indicated RH and temperature at each set point before any adjustment. As-found data proves whether the environmental conditions logged for stored product or a controlled area were actually in range.
Step 3: Compare against the reference at each set point. Generate stable humidity levels across the required span, allow full stabilization at each point, and record the instrument reading against the reference hygrometer along with the chamber temperature.
Step 4: Adjust, repair, or reject as required. Apply the manufacturer’s RH offset or span correction where the design allows, replace contaminated filters or drifted sensor elements, and service the unit as needed. Instruments outside specification after service are documented and returned as limited-use or rejected.
Step 5: Perform “as left” verification and issue documentation. Re-run the full set-point series after any adjustment and issue an ISO/IEC 17025 accredited certificate with as-found and as-left RH and temperature data, measurement uncertainties, and NIST traceability.
Pro tip from our lab: Always request as-found/as-left data on your certificate. Without it, you can’t assess whether measurements taken before calibration were reliable — a common audit finding.
How Often Should You Calibrate a Hygrometer?
| Usage Profile | Recommended Interval | Notes |
|---|---|---|
| Daily industrial / field use | 6–12 months | Shorten after drift or overload events |
| General lab / bench use | 12 months | Industry-standard default |
| Regulated environments (ISO 9001, FDA, A2LA audits) | Per quality system, typically 12 months | Interval must be documented and justified |
ISO/IEC 17025 does not specify fixed calibration intervals. It requires that intervals be reviewed and adjusted as necessary to maintain confidence in the equipment. Recommended intervals are typically 6–12 months, adjusted based on documented risk assessment and historical stability data per the lab’s calibration program. A2LA and ANAB are accreditation bodies — distinct from quality-system frameworks such as ISO 9001 or FDA requirements.
Frequently Asked Hygrometer Questions
Q: How much does hygrometer calibration cost?
A: Hygrometer calibration cost depends on the number of humidity set points and the span covered, whether the temperature channel is calibrated with it, whether the sensor is integral or a remote probe, and whether accredited (17025) certification is needed, and whether accredited (17025) certification is required. Contact Tra-Cal for a quote.
Q: Can I calibrate a hygrometer myself?
A: You can perform verification checks against a known reference, but formal calibration requires traceable standards with a 4:1 accuracy ratio and documented uncertainty.
Q: What is the difference between calibration and adjustment?
A: Calibration is the documented comparison against a standard; adjustment is the correction made when readings fall outside tolerance.
Q: How long does calibration take?
A: Standard turnaround is typically 3-5 business days; Tra-Cal offers expedited service options.