Calibration of a humidity chamber involves verifying and adjusting its performance to ensure it produces accurate and consistent humidity levels. Here's a step-by-step guide:

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1. Preparation

1. Read the Manual: Familiarize yourself with the chamber's operation and calibration instructions provided by the manufacturer.
2. Gather Required Tools:
   • Hygrometer or reference instrument (calibrated and traceable to national standards).
   • Data logger (optional for continuous monitoring).
   • Calibration salts or a humidity generator (if required).
   • Tools for making adjustments, as per the chamber's specifications.
3. Stabilize the Environment: Ensure the chamber is in a stable ambient environment free from significant temperature or humidity fluctuations.

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2. Perform Calibration

Option A: Using Reference Instrument

1. Place the Reference Instrument:

   • Position the calibrated hygrometer inside the chamber at the test point.
   • If the chamber is large, place sensors in multiple locations to ensure uniformity.

2. Set the Humidity:

   • Program the chamber to specific humidity levels (e.g., 30%, 50%, 70%, and 90% relative humidity).
   • Let the chamber stabilize at each set point.

3. Record the Readings:

   • Compare the chamber's displayed humidity with the reference instrument's reading.
   • Note deviations at each set point.

4. Repeat for Temperature Variation:

   • If the chamber has temperature control, perform the same tests at different temperatures to verify combined accuracy.

Option B: Using Saturated Salt Solutions

1. Prepare Salt Solutions:

   • Use salts like sodium chloride (NaCl) or magnesium chloride (MgCl₂) to create known humidity levels in sealed containers.
   • Refer to a salt reference table for expected RH levels at specific temperatures.

2. Place Solutions Inside:

   • Place the solution container in the chamber and allow stabilization.

3. Measure Humidity:

   • Compare the chamber's readings with the expected humidity from the salt solution.

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3. Adjust the Chamber (if needed)

• Use the calibration interface or manual adjustments to correct deviations.
• Follow the manufacturer’s procedure for entering calibration offsets.

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4. Verification

• After adjustment, recheck all set points to confirm the accuracy.
• Perform a stability test by running the chamber for extended periods and observing deviations over time.

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5. Document Calibration

• Record:
  • The reference instrument details (serial number, last calibration date).
  • The observed deviations and corrections made.
  • Environmental conditions during calibration.
  • The date and technician's name.

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6. Schedule Routine Calibration

• Regularly calibrate the chamber (e.g., annually or as specified by quality standards).

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By maintaining proper calibration, your humidity chamber will provide reliable and precise conditions for testing or storage.