How to maintain the measuring instruments?

“Our body is like a machine. What will happen if regular health check-up is not done? Regular exercise not done?  We may fall ill. Similarly in the case of  measuring instruments, if we do not do the proper, regular maintenance, it will also fail.” 

Types of Inspection Equipment:

Measuring Instruments:

  • Micrometer,
  • Vernier Caliper,
  • Height Gauge,
  • Bore Gauge,
  • Universal Bevel Protractor,
  • Torque Wrench etc.

Gauges

  • Plug Gauge,
  • Snap Gauge,
  • Length Gauge,
  • Ring Gauge etc

Testing Machine:

  • Hardness Tester,
  • Plating thickness tester,
  • Penetration testing machine
  • UTM

Accuracy Check of  Inspection Equipment:

Daily / weekly periodical accuracy check at defined frequencies shall be carried out to find out if any error in the measuring device has occurred during routine handling. Also method should be adopted to carry out daily maintenance of measuring equipment’s & devices.

  • Daily cleaning of instruments & gauge
  • Visual inspection of instruments & gauge
  • Check any wear & tear of instruments & gauge
  • Proper storage of instruments & gauge

Calibration of measuring instruments :

Calibration is correctness made or set with a standard ( Master ) device to ascertain & correct the accuracy of a measuring device.   In order to properly control the calibration work & to ensure that no inspection equipment remains without calibration,  it is better to make an annual plan for calibration & adhere to it.  

Inspection standards should be prepared to specify the inspection item, judgment criteria, daily maintenance, periodic accuracy method & inspection frequency for each type of measuring instrument, gauge & testing machine.  

Measuring Instruments Control:

All the inspection instruments should be identified by a unique control number. A sticker should be put on all inspection instruments with Control Number ( Instrument ID), calibration date & Next calibration date.

measuring instruments
Calibration sticker

Inspection Equipment’s Registration :

A control register shall be maintained for inspection instruments with the following detail:

  • Name of  Instruments
  • Model
  • Manufacturer
  • Date of Purchase
  • Date of installation
  • Area of installation
  • Control Number
  • Person/shop that uses it
  • Frequency of calibration

If any instruments are scraped then its control number shall not be used for the new instruments and the same needs to be captured in the control register by writing ‘Obsolete’ or ‘Scrap’.

Instruments History Cards:

Measuring equipment history cards shall be maintained recording the event of calibration & maintenance activities respectively. Such a history card should also contain repair or correctness done in the measuring equipment.

Instrument History Card

Action in case of measuring device found out of calibration:

A documented system should be defined for action to be taken in case of measuring device found out of calibration,

  • Inform to customer
  • The retroactive action to be taken on the products on which judgment has been made by usage of such equipment since the last calibration.

Importance of calibration of instruments :

The accuracy & reliability of all measuring instruments would be doubtful if the instruments used were not calibrated. Calibration ensures that a measuring instrument displays an accurate and reliable value of the parameter/ dimension being measured.  

The accuracy of all measuring devices degrades over time due to normal wear & tear. However change in accuracy can be caused by electric or mechanical shock or hazardous manufacturing equipment ( oil & metal chips etc). Depending upon the type of instrument & environment in which it is being used it may degrade very quickly or over a long period of time.  

Frequency of Calibration :

A measuring device should be calibrated :

  • According to the recommendation of the manufacturer
  • After any mechanical or electrical shock
  • After any excess or continuous use
  • Effect of any environmental condition like temperature, humidity, dust etc.
  • Periodically (Yearly, half-yearly)

Instrument Calibration Plan:

Instrument Calibration Plan

Calibration Certificate:

Calibration certificate contain below information,

  1. Name & address of the laboratory
  2. A unique control number of the calibration certificate.
  3. Name & address of the customer 
  4. Identification of the method & the master used with calibration detail
  5. Description, status & identity of the calibration item
  6. Due date of the calibration along with the date of calibration
  7. Calibration result along with judgment criteria
  8. Name, designation & signature of the authorized person who is in charge to grant the calibration certificate with the stamp of the laboratory.
  9. The environmental condition under which calibration was carried out
  10. NABL logo on certificate showing scope of laboratory & accreditation certificate issue number

Retention Period of Calibration Record :

The retention period for the calibration record shall be a minimum of 3 years. Calibration records should be available and preserved for the specified period as per the procedure.

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