To describe a standard operating procedure for the calibration of weighing machines.
1.0 PURPOSE :
To describe a standard operating procedure for the calibration of weighing machines.
2.0 SCOPE:
The standard operating procedure describes in detail the method for the calibration of both mechanical and electronic weighing machines in the plant. The procedure holds good for the in-house calibration only.
3.0 RESPONSIBILITY:
The responsibility of calibrating the weighing machines lies with the staff of rank not lower than the Supervisor of maintenance department.
The responsibility of preparation, review and approval of the standard operating procedure lies with the Manager (Maintenance), Head of Production and Head of QAD respectively.
4.0 METHOD:
4.1 Select the standard weights duly calibrated by Department of Legal Metrology, Weights and Measures Department or their authorised agency and suitable for calibration range / capacity of the weighing machine.
4.2 Prior to calibration, adjust the balance to ‘Zero’ reading by adjusting screw / tare weight.
4.3 Calibrate the weighing machine at the calibration range with 3-4 standard weights. Calibration / Operating range and suitable standard weights for different weighing machines shall be as follows.
|
S.No. |
Capacity of Weighing Machine |
Calibration / Operating Range |
Suitable standard weights for calibration |
|
1. |
5 Kg. |
100 g. to 4 Kg.
|
0.1 0.5 2.0 4.0 |
|
2. |
60 Kg. |
5 to 50 Kg
|
5 10 30 50 |
|
3. |
100 Kg.
|
10 to 90 Kg. |
10 50 70 90 |
|
4. |
150 Kg. |
10 to 140 Kg. |
10 30 100 140 |
|
5. |
200 Kg. |
10 to 190 Kg. |
10 50 100 190 |
|
6. |
300 Kg. |
50 to 250 Kg. |
50 100 200 250 |
4.4 Place the standard weights on the weighing machine platform and record the corresponding reading of the weighing machine as per format xxxxx shown in Annexure-I.
4.5 If there is any difference between the standard weight and the weight displayed by the weighing machine, the difference shall be recorded.
4.6 If the weighing machine shows “ZERO” difference a white coloured tag shall be tied to the machine.
4.7 Acceptance criteria :
|
S.No. |
Capacity |
Accuracy |
Acceptance criteria |
|
1. |
5 Kg mechanical type weighing machine |
± 1 g |
± 2 g |
|
2. |
5 Kg digital type electronic weighing machine |
± 1 g |
± 2 g |
|
3. |
60 Kg digital type electronic weighing machine |
± 10 g |
± 20 g |
|
4. |
100 Kg digital type electronic weighing machine |
± 10 g |
± 20 g |
|
5. |
150 Kg digital type electronic weighing machine |
± 10 g |
± 20 g |
|
6. |
200 Kg digital type electronic weighing machine |
± 100 g |
± 100 g |
|
7. |
300 Kg mechanical type weighing machine |
± 0.5 Kg |
± 0.5 Kg |
4.8 If the weighing machine shows the difference within the acceptance criteria a pink coloured tag shall be tied to the weighing machine.
4.9 If the weighing machine shows difference beyond the acceptance criteria repair the machine.
4.10 Maintenance department shall rectify the problem incase of mechanical weighing balances by following checkpoints.
? Check the platform bushes and thrust balls for its perfect seating on knife edges, replace the spare parts as required
? Check the tare bar brackets.
? Adjust the tare weights.
4.11 Maintenance department shall rectify the problem incase of Electronic weighing balances by following check points.
? Check power supply.
? Check the load cell which is attached to the platform.
? Check the loose connections.
? Clean power circute board (PCB) to remove any deposits on the circuit.
4.12
After necessary repairs recalibrate the weighing machine as per steps 4.3 and 4.4 and record the recalibration data as per format xxxxx shown in Annexure-II.
4.13 Even after servicing by the maintenance department, if the machine not showing the readings within the acceptance criteria machine shall be repaired by out side service agency. If the machine is not repairable the same shall be replaced with new. Replacement data shall be recorded in history card.
4.14 Whenever the weighing machine is rectified / replaced with another prior to scheduled calibration due date, the same shall be informed to Quality Assurance Department, for taking necessary action regarding variation of the quality and yields of the batches carried out with the machine during the period of previous date of calibration and the date of rectification/replacement. Recalibration data shall be recorded as per format xxxxx as shown in Annexure-II and also enter in the history card of the weighing machine.
4.15 Apart from recalibration, the calibration shall be followed as per calibration schedule.
4.16 Calibration tag for weighing machine shall have the following particulars.
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CALIBRATION TAG FOR WEIGHING MACHINE |
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1. |
Weighing M/C No |
: |
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2. |
Location |
: |
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3. |
Calibration / Operating range |
: |
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4. |
Difference |
: |
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5. |
Acceptance criteria |
: |
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6. |
Date of calibration |
: |
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7. |
Next due date of calibration |
: |
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8. |
Calibrated / Recalibrated by |
: |
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9. |
Signature |
: |
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4.17 Frequency: Calibration shall be carried out on 1st and 16th date of every month
± 2 days as per calibration schedule shown in Annexure-III.
4.18 A master list of weighing machines showing weighing machine No., description location and calibration/operating range shall be prepared as per Annexure-IV.
4.19 Manufacturer’s serial number of the weighing machine is considered as Machine identification number in the calibration tag as well as in calibration chart.
5.0 RECORDING:
The responsibility of recording the calibration readings as per Annexures lies with the staff of rank not lower than supervisor of maintenance department.
Weighing machines, calibration, engineering
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