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 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:

1. Make sure that the balance is kept clean & placed on flat platform free from vibrations. 
2. Ensure that the calibration status is valid. 
3. Ensure that the spirit level is in the center of the circle. 
4. Connect the power cable to the mains and switch ‘ON’. 
5. Automatically self-checking starts & ends with OFF. 
6. Press ON/OFF key, all the display will glow. 
7. Press “TARE KEY”, 0.0000 marks appears on the display. 
8. The stability of the reading is obtained and is indicated by an arrow mark on the left side of the display. 
9. Once the stability is attained, the balance is ready for weighing. 
10. 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. 
11. 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: Air bubble must be in center of 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 and press the Tare key and wait till 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 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 sign 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 operation procedure described above & proceed for external calibration. 

PEOPLE 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 following equation: 

• Repeat above steps for 100g weight, and record the results as per Attachment - II 
• Acceptance Criteria: 

1. Each weighing shall not differ more than 0.1% of the actual weight. 
2. 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

PEOPLE ALSO READ: SOP for Calibration of Weight Box