Instrument Calibration Guide

Safety, quality, and consistency – what do these have in common? The standards for all three reduce if you don’t calibrate your instruments regularly!

What is Instrument Calibration?

Instrument calibration

Instrument calibration is the process of comparing the measurements made by the instrument to be calibrated against a known measurement of either standards or an instrument known to be making measurements that exceed the acceptable limits of accuracy and precision.

Typically, a standard with 10 times the accuracy is preferred, but most regulating organizations and authorities accept a 3:1 accuracy ratio.

What is the Purpose of Instrument Calibration?

There are five main reasons for calibrating instruments:

  1. Ensuring the instrument is making consistent measurements and displaying the correct readings.
  2. Determining the precision, deviation, and reliability of the measurements, which is important for manufacturers as part of design qualification.
  3. Establishing the instrument’s reliability, i.e. whether it can be trusted.
  4. Mapping the ‘drift’ (through documentation), which is the tendency of the measurements to become inaccurate over time and with repeated use.
  5. Maintaining adherence to industry standards, government regulations, and/or quality assurance norms like the current good manufacturing practice (cGMP).
  • Precision – Denoted as either a percentage or fixed measure in (±), precision is the ability of an instrument to consistently reproduce repeated measurements under the same conditions (the maximum significant digits or decimal points of the measurements which can be considered reliable).
  • Accuracy – The degree of closeness or the ability of an instrument to measure a value compared to the actual value of the quantity being measured.

Types of Instruments that Need Calibration

Instruments of all sorts operate by making some sort of measurement. This could include everything from physical attributes like length, width, and height to electricity and pressure. When it comes to calibration, you need to calculate how much of an effect an instrument actually has on your product or service quality.

There are various methods for testing the degree of effect on quality, but here’s a list of instruments that frequently have a major effect and tend to stray from true measurements:

  • Optical Instruments
  • Pressure and Torque Instruments
  • Gauges
  • Probes
  • Electrical Measuring Instruments
  • Radiation-Sensitive Instruments
  • Field Instruments

Instrument Calibration Frequency

The frequency of calibration is also largely dependent on the instrument’s impact on quality and its tendency to drift from true measurement. Based on this information, a general calibration regimen can be created for each instrument. The interval between calibrations can be established on the following basis:

  • Weekly
  • Monthly or bi-monthly
  • Quarterly, semi-annually, or annually
  • As needed (per the scenarios mentioned below)

When do Instruments Need to Be Calibrated?

Here is a guide that outlines when calibration is needed as part of good manufacturing practices (GMP):

  • While testing new instruments (Part of DQ IQ OQ PQ)
  • After repairs and requalification when instruments are sent for calibration
  • Before and after making critical measurements
  • After an event (a bump, fall, or electrical surge, when a safety check should also be performed)
  • When the accuracy is suspect or the measurements are questionable
  • As per requirements (depending on the criticality or as part of a calibration schedule)
  • Depending on the task (some experiments might require prior calibration)
  • As per the manufacturer’s recommendations

Methods and Procedures for Calibration

There are a few different methods that may be used for calibration, depending on the desired results of the calibration and regulatory authorities’ requirements, like FDA guidelines:

  • ISO 17025 Accredited Calibration – This is one of the strictest forms of calibration. It typically requires a measurement report that details the measurements made against a standard as found (before calibration) and as left (after calibration). All the measurements and standards used need to be traceable to an acceptable national or international organization for standards. In case the calibration is undertaken by a calibration service provider, a certification is also issued.
  • Calibration with Data – The procedures for calibrations with data are quite similar to accredited calibration except that they are not accredited to the ISO standard and are not accompanied by data on measurement uncertainties.
  • Standard Calibration – This is the preferred form of calibration for instruments that are either non-critical to quality or are not required for accreditation and license purposes. To ensure they are still effective, traceable standards should be used and performance (as used and as found) should be documented.

Importance of Calibration Services

Undertaking calibration in-house isn’t always the best or most cost-effective way. Even if you have an in-house calibration setup, you will at some point require a calibration service provider. Some of the benefits of enlisting external calibration services include:

  • Quality – Most calibration service providers are ISO certified and accredited to the international standards for calibration laboratories (ISO 17025). They operate under strict guidelines, meet the manufacturer’s requirements, and are authorized to issue calibration certificates.
  • Speed – Calibration services can be a faster alternative to taking the instruments to a shop for calibration. The shorter downtime and lower manpower and logistics requirements can lead to significant savings.
  • Comprehensive Reports – The reference standards used by calibration services often have higher accuracy and precision, resulting in better, more accurate calibrations.

No Comments

    Leave A Comment

    1047 Serpentine Lane, Suite 500, Pleasanton, CA 94566
    Call us today 1-877-799-0922
    Malcare WordPress Security