Calibration procedure for measuring instruments

Purpose :

The purpose of the calibration procedure is to ensure that all measuring, test equipment and gauges are maintained in a suitable state and remain capable of measuring to the required accuracy.

Scope :

The applicability of this procedure is for calibration of all monitoring and measuring equipment and gauges used for monitoring/measuring product and process characteristics within the organization.

Responsibility :

Head QA is responsible for establishing and maintaining this procedure.

Procedure :

Master list of Instruments :

Identify all the Instruments and gauges for measurement as required for all the stages of production. Prepare a list covering all the instruments & gauges available in the organization and maintain a Master list of instruments & gauges. Provide unique identification numbers to all monitoring and measuring equipment and gauges.

Calibration Plan :

A “Calibration Plan” is prepared for the instruments and gauges as per the appropriate frequency. The Calibration frequency is based on uses, make & recommendations of manufacturers etc. Calibration plan containing the date of calibration, Due date and method of calibration. Calibration is performed by either Internal or by External agencies.

Internal Calibration :

For performing Internal calibration, a proper lab is required and a qualified & experienced person is required for doing the calibration. Also calibrate the master instrument from the NABL-approved lab and maintain the record.

External Calibration :

For performing External calibration, the External Agencies used for calibration shall be accredited/approved by a National Laboratory (NABL) or ISO / IEC 17025 certified.  Where a qualified laboratory does not exist for a particular piece of equipment, calibration services may be performed by the original equipment manufacturer (OEM) and their names shall be included in the approved Supplier list.

The scope of the external agency also checks before doing calibration from any agency to check whether the calibration of that equipment is within the scope of that agency or not.

The calibration activities are carried out as per the plan and the calibration certificate is verified for the acceptance of the instrument with the defined standard for acceptance criteria. Receipt of Calibration Certificate from external sources and examine the same for adequacy or result under the acceptance criteria.

In case the equipment shows NG values or results found out of acceptance criteria, send back it for repair, if possible. Otherwise, put a reject sticker or red paint mark over it and update the relevant records accordingly.

New Instrument :

In case of a new / repaired instrument ensure that it is calibrated before bringing it into use. Also update the Master List, Calibration plan and individual instrument calibration record (Instrument History card)

Master Instruments :

Keep the Master Instrument in safe and secure condition and ensure that the Master Instrument is not used for regular purposes. Cleaning of Master Instrument is ensured and application of preservatives as applicable while storing for a longer period.

Instruments handling :

Handle and store the calibrated instrument in such a way that their accuracy and fitness for use are maintained. In case the instrument falls down during use or gets damaged, send the same to the Standard Room for checking/repairing or re-calibration, if required.

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Out of Calibration :

In case the date of calibration is over the grace period of the same will be given of 15 days. Also the material inspected with that gauge shall be identified separately. If possible the calibration of instruments should not be later than the due date.

During Calibration following calibration records are to be checked:

  • Follow the engineering changes that impact the measurement system.
  • Check that any specifications readings are received from the agency.
  • Check the risk of that out-of-specification reading on the product.
  • During Calibration, if any instrument is found to be out of calibration (the error exceeding the acceptance criteria), an out-of-calibration report is to be raised. One of the following actions will be taken on the equipment: a) Recondition and re-calibrate b) Replace the equipment and document the validity of the previous inspection and the test results.
  • Wherever evidence is available for shipment of the suspect product, the customer is to be notified.
  • Check & verify the specification after re-calibration.
  • Verify the latest software which are used for product and process and maintained record.
  • Maintain the calibration record of all instrument

Measurement System Analysis (MSA) :

Variable MSA :

  • Identify the instrument & prepare a plan that is needed for the MSA study.
  • MSA plan is prepared with the appropriate frequency or defined by the customer.
  • The appraiser is selected based on the responsibility of product inspection and the use of  instruments
  • MSA study is conducted as per plan & Gauge R&R is calculated.
  • Interpretation of Gauge R&R  is conducted and analyzed the results are as :
  1. Measurement System is acceptable if gauge R&R is <10%
  2. Measurement System is may be acceptable if gauge R&R is >10% and <30%
  3. Measurement System is not acceptable if gauge R&R is >30%

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Attribute MSA :

  • Prepare Attribute MSA Plan
  • Check Effectiveness
  • Check Miss Rate
  • Check False Alarm
  • The effectiveness of each appraiser should be more than 90%
  • The Miss Rate of each appraiser should be less than 2%
  • The false Rate of each appraiser should be less than 5%

For more details about Attribute MSA

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