SOP for Operation and Calibration Procedure for Analytical Balance

OBJECTIVE 

To lay down the procedure for the operation and calibration of the Analytical Balance for better and error-free use.

SCOPE 

This procedure is applicable for Analytical Balances installed in the QC Department, IPQC Department & Dispensing Department.

RESPONSIBILITY 

It is the responsibility of QC Executives to follow the procedure without deviation. 

ACCOUNTABILITY 

Manager – Quality Control 

PROCEDURE 

Operation Procedure:

• Make sure that the balance is kept clean & placed on a flat platform free from vibrations.
• Ensure that the calibration status is valid.
• Ensure that the spirit level is in the center of the circle.
• Connect the power cable to the mains and switch ‘ON’.
• Automatically self-checking starts & ends with OFF.
• Press the ON/OFF key and all the displays will glow.
• Press “TARE KEY”, and 0.0000 marks appear on the display.
• The stability of the reading is obtained and is indicated by an arrow mark on the left side of the display.
• Once the stability is attained, the balance is ready for weighing.
• Place the material to be weighed on the pan & note down the reading after the arrow mark appears on the left side of the display.
• Clean the balance immediately after weighing.

Preliminary Checks For Balance Calibration:

Spirit Level Check (Balance Leveling):

• Adjust the air bubble to the center of the inner circle of the indicator by rotating the two leveling screws at the rear base of the balance.
• Acceptance Criteria: The air bubble must be in the center of the inner circle.

Pan Cleaning and Adjustment:

• Before placing the std. weight/butter paper/glassware, clean the pan properly. Also, ensure that the pan is adjusted properly (if not adjusted before).
• Acceptance Criteria: Pan must be cleaned and centrally placed.

Zero Error Check:

• Close the sliding doors of the balance press the Tare key and wait till the LCD shows zero.
• Acceptance Criteria: LCD should display zero on the LCD screen.

Handling of Weight Box:

• Ensure that the weights used are calibrated and certified on a regular basis.
• Always use forceps/tweezers to place the weights on the balance pan.
• Do not drop the weights with force on the pan of the balance, to avoid any variation in the results.
• Weights used for calibration should always be cleaned with tissue paper before & after each use.
• Acceptance Criteria: Weights should not have any denting or damage signs and should be cleaned before and after each use.

Calibration Procedure:

Frequency: 

• Each working day: Spirit Level Check, Pan cleaning and adjustment, Zero Error Check, Accuracy.
• Weekly & after maintenance: Spirit Level Check, Pan cleaning and adjustment, Zero Error Check, Accuracy, Precision/Measurement Uncertainty, and Corner accuracy/eccentricity test.
• After preliminary checks are completed operate the instrument as per the operation procedure described above & proceed for external calibration.

ALSO READ: SOP for Calculation of Weighing Range of Analytical Balance

Accuracy:

• For daily calibration use 50 mg & 100mg. Place each weight on the weighing pan. Note down the observed weight.
• For Weekly calibration use 50mg, 100mg, 200mg, 500mg, 1g, 5g, 10g, 50g, and 100g weights.
• Record the readings as per Attachment - I for daily calibration and as per Attachment - II for Weekly calibration.
• Acceptance Criteria: Each weighing should not differ by more than 0.1% of the actual weight.

Precision/ Measurement Uncertainty:

• Place the 50mg weight on the weighing pan & note down the observed weight.
• Repeat the above steps nine times.
• Record the results as per Attachment - II
• Calculate the Standard Deviation (SD).
• Calculate the measurement uncertainty using the following equation:

• Repeat the above steps for 100g weight, and record the results as per Attachment - II
• Acceptance Criteria: Each weighing shall not differ more than 0.1% of the actual weight.
• Measurement uncertainty should not be more than 0.001.

Corner Accuracy/Eccentricity Test:

• Place 50g weight on the center, front-left, front-right, back-right and back-left side of the weighing pan (As shown below) and note down the weight for each position.

1. Center
2. Front - Left
3. Front - Right
4. Back - Right
5. Back - Left 

• Calculate the difference between the observed weight and the certified weight.
• Record the results as per Attachment - II for Weekly calibration.
• Acceptance Criteria: Each weighing shall not differ more than 0.1% of the actual weight.

ATTACHMENTS

Attachments I: Preliminary Checks & Daily Calibration Record of Analytical Balance 

Attachments II: Calibration Record of Analytical Balance

ABBREVIATIONS

QC – Quality Control
LCD – Liquid Crystal Display

REVISION HISTORY

Nil

ALSO READ: SOP for Operation of Malvern Particle Size Analyzer