What Is Calibration?
Calibration is the high level, controlled and documented process of measuring traceable calibration standards over the full operating range of the gauge and verifying that the results are within the stated accuracy of the gauge. If necessary, gauge adjustments are made to correct any out-of-tolerance conditions.
They are typically performed by the gauge manufacturer or by a qualified laboratory in a controlled environment using a documented process. The coating thickness standards used in the calibration must be such that the combined uncertainties of the resultant measurement are less than the stated accuracy of the gauge. Typically a 4:1 ratio between the accuracy of the standard and the accuracy of the Gauge is sufficient. The outcome of the process is to restore/realign the gauge to meet/exceed the manufacturer’s stated accuracy.
Calibration Interval
This is the established period between recalibrations (recertifications) of an instrument. As per the requirements of ISO 17025, DeFelsko does not include calibration intervals as part of Certificates issued with our coating thickness gauges.
For customers seeking assistance in developing their own calibration intervals, we share the following experience. Non-age related factors have shown to be more critical in determining intervals. These factors are primarily the frequency of use, the application in question, as well as the level of care taken during use, handling and storage. For example, a customer that uses the gauge frequently, measures on abrasive surfaces, or uses the gauge roughly (i.e. drops the gauge, fails to replace the cover on the probe tip for storage, or routinely tosses the gauge into a tool box for storage) may require a relatively shorter interval.
From both theoretical analysis and practical experience, the impact of temperature and moisture on the gauge is very minimal. In addition, manufacturing processes are designed to minimise post calibration changes in gauge performance. Even in the event of drift, PosiTector 6000 measurements are typically linear and are thus compensated for prior to use by the “zero” function of the gauge.
DeFelsko recommends that customers establish gauge calibration intervals based upon their own experience and work environment. Customer feedback suggests one year as a typical starting point. Furthermore our experience suggests that customers purchasing a new instrument can safely utilise the instrument purchase date as the beginning of their first calibration interval. The limited effect of age minimizes the importance of the actual certificate date.
Calibration Certificate
This is a document that records actual measurement results and all other relevant information to a successful instrument calibration. Certificates clearly showing the traceability to a national standard are included by DeFelsko with most new recalibrated or repaired instruments. Please CLICK HERE to see an example of a Certificate.
Traceability
Traceability is the ability to follow the result of a measurement through an unbroken chain of comparisons, all the way back to a fixed international or national standard that is commonly accepted as correct. The chain typically consists of several appropriate measurement standards, the value of each having greater accuracy and less uncertainty than its subsequent standards.
Recalibration
Recalibration, also referred to as recertification, is the process of performing a calibration on a used instrument. Recalibrations are periodically required throughout the life cycle of an instrument since probe surfaces are subject to wear that may affect the linearity of measurements.
Prices
A new certificate for all coating thickness gauges costs £99 + VAT . A new certificate for PosiTector DPM Dew Point Meter costs £125 + VAT and the PosiTest Adhesion Tester is £215 + VAT. Every DeFelsko gauge is sent back to the factory in Ogdensburg, USA to produce this traceable calibration certificate. Usual turnaround time is 7 days (SEE BELOW).
Timescale
DFT Instruments send gauges back to DeFelsko for calibration on a Monday. These gauges are back with us the following Monday and will be dispatched for delivery on the Tuesday. On occasions it may be delivered to you on the Wednesday. Adhesion testers and coating thickness gauges are calibrated on site and can expect a turnaround time of a maximum of 48 hours.