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:
- Make sure that the balance is kept clean & placed on 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 ON/OFF key, all the display will glow.
- Press “TARE KEY”, 0.0000 marks appears 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: 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:
- 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.
- Center
- Front - Left
- Front - Right
- Back - Right
- 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
ABBREVIATIONS:
Attachments II: Calibration Record of Analytical Balance
QC – Quality Control
LCD – Liquid Crystal Display
LCD – Liquid Crystal Display
PEOPLE ALSO READ: SOP for Calibration of Weight Box
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