SOP for Calibration of Humidity Indicator/ Thermo-Hygrometer

OBJECTIVE

To define the procedure for calibration of the Humidity Indicator/Thermo-hygrometer/ Humidity Data logger in a laboratory.

SCOPE

This Calibration Procedure is applicable for the calibration of Humidity Indicator/Thermo-hygrometer/ Humidity Data logger in a laboratory by comparison method for

RESPONSIBILITY

• Calibration-engineer will perform the Calibration and note down the details and measurements on the observation sheet.
• The technical/Quality Manager or his designee will check the observation sheet and approve the Calibration Certificate.

STANDARD & EQUIPMENT USED

Range (33 to 75)%RH @25 ˚C, Using Standard Humidity salts.

Support Equipment: The supporting equipment is,

• A Digital Temperature & Humidity Data Logger (to measure temperature & relative humidity of air)

ENVIRONMENTAL CONDITION

At Lab

1. Temperature: (23 ± 2) °C
2. Relative Humidity: 30% to 75% RH

On-site

1. Temperature : (23 ± 5) °C
2. Relative Humidity: 30% to 75% RH

• If stated environmental conditions are jeopardized then calibration work will be stopped & report to the technical manager for further instruction

PRINCIPLE OF CALIBRATION

Humidity is the amount of water vapor in the atmosphere caused by condensation and evaporation. It can be measured as absolute humidity (the amount of water vapor in a unit volume of air), or as relative humidity.

INSPECTION OF THE UUT

All the UUT received in the laboratory shall be inspected for the following criteria:

1. UUT should not be broken.
2. The display should be clear.

PROCEDURE FOR CALIBRATION

• Check the calibration points from the job card.
• Check the temperature and humidity condition of the laboratory/calibration activity area during calibration and record the same Observation sheet.
• Note down the details of UUT in the Observation sheet.
• Clean the UUT with the help of a clean cloth or lint-free duster.

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Calibration of Humidity

• Maintain the temperature of the room to nearly 25˚C by using an Air Conditioner.
• Take the bottle of standard humidity salt & put the instrument inside the port of the bottle
• After stabilization take 5 readings at 1-minute intervals of standard & UUT in & note down readings in the observation Sheet and apply the correction factor.
• Repeat calibration at different points as per the job card.
• Affix calibration sticker on UUT.
• Calculate the uncertainty of measurement at 5 repeated readings at the same Measurement points. Max. Uniformity and Stability should be taken during uncertainty calculation.
• Prepare the calibration certificate.
• The technical/Quality Manager or his designee shall review the observation sheet and certificate and issue the certificate to the customer.

SAFETY PRECAUTION

• The standard sensor and the UUT shall be handled carefully.
• Readings are always taken at stable condition of the humidity cabinet.
• Standard Humidity Solution bottle should be kept closed tightly after use.

ABBREVIATIONS

CP: Calibration Procedure

STD: Standard

UUT: Unit under test

RH: Relative Humidity

TEMP.: Temperature

REFERENCE

ASTM E104-20A

ESTIMATION OF THE UNCERTAINTY

An estimate characterizing the range of values within which the true value of the measurand lies. The technical Manager is responsible for identifying the uncertainty components that are important to particular calibrations undertaken by the laboratory.

The standard uncertainty of measurement U(xi) in calibration is evaluated by two different methods denoted by Type A and Type B.

The Type-A method of evaluation of uncertainty utilizes the rules of basic statistics and quantitatively is equal to the mean of the standard deviation of a set of the measured values.

REVISION HISTORY

Nil

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