Can Calibration Intervals Be Extended?
Calibration is a traceable process that ensures your measurement instrumentation is performing reliably within its specifications. It is also one of the unavoidable costs of test equipment ownership – a cost that you continue to carry as long as you operate the instrument in an environment that demands reliably accurate measurements. The pressure to reduce maintenance costs in any business is a reality, and even more so in those organizations that use multiple test instruments. So can the cost of calibration be reduced in the long term? Some companies have done so by extending the calibration interval time or time needed for recalibration.
In the test and measurement industry, most manufacturers specify a 12-month calibration interval for the majority of their instruments. (Other factors affecting calibration intervals are government requirements and contract specifications.) This interval is usually determined by R&D and quality engineers before the product is released into the market. Some of the key influences that lead to such decision include:
· Data from similar products
· Data from subassemblies and individual components used in the instrument
· Influence of environment
· Operating conditions
· Required uncertainty in measurement
Although a 12-month calibration interval is pretty much the norm, there are increasing numbers of instruments that are designed for 36-month calibration intervals, due to innovations that incorporate built-in self-monitoring and self-adjusting hardware and firmware to maintain maximum accuracy over a longer time span.
Even if your instrument has been recommended for a 12-month calibration interval by design by the manufacturer, there may be a possibility of stretching it beyond that. However, it can take several iterations after the initial interval adjustments to arrive at the optimal calibration, since the instruments may be less reliable than expected or the usage may not be as anticipated.
There are several methods for reviewing the calibration interval, and most of these processes usually involve some form of statistical analysis. This requires historical calibration data, which means you would need to complete at least two calibration cycles. (The more the better, as more data will help to predict more accurately how the instrument will perform with an extended calibration interval.) The data would also indicate how much the instrument has drifted over time. Other data needed are those of similar models. Regression analysis and data fitting are then performed to predict future behavior of the instrument. For complex instruments or specification parameters, automatic data processing software is needed for the analysis.
If you have a large number of instruments in your pool, you may decide to prioritize which instruments should go for calibration interval extensions and which ones remain as per the manufacturer’s recommendation. To ensure that your organization continues to operate smoothly, it is advisable to calibrate those critical instruments as often as possible; those that are less critical will be good candidates for the review of calibration extension. This helps to balance costs and risks.
For more advice about calibrating your measurement test equipment, or for ways MAT can help reduce the cost of test equipment ownership, please call us at 877-871-TEST or contact us today.