Calibration Procedures
We follow formal, documented procedures when performing calibration. These calibration procedures are maintained in our quality system, pursuant to document control guidelines.
Test points
If you require specific test points for an instrument, we will use those test points when performing the calibration. If not, we prefer to use a minimum of five test points to establish linearity. Depending on the instrument type and range, we typically chose test points consistent with one of the following schedules:
10%, 30%, 50%, 70% and 90% of full span
0%, 25%, 50%, 75% and 100% of full span
20%, 40%, 60%, 80% and 100% of full span
If an instrument, such as a pressure gauge, has mechanical moving parts, then we check hysteresis by calibrating the instrument both in the upscale and downscale direction, for a total of 10 test points. Usually, if a pressure gauge is going to fail calibration, it will do so on the downscale calibration.
Range
We calibrate instruments throughout their full ranges unless you request that a calibration be performed over a more narrow, application specific range, or at a point of use.
Accuracies
We maintain a database of manuals and manufacturer specifications to support the data we use for manufacturer accuracies.
We record both the manufacturer accuracy and user defined accuracy, as available, on our calibration certifications, so the user can clearly see the instrument’s capabilities relative to what they expect from it. The user defined accuracy, when available, is treated as the default for determining an instrument’s pass/fail criteria.
In the event that neither a manufacturer accuracy nor user defined accuracy is available, we perform an “as-found” calibration and do not state whether the instrument has passed or failed.
Standards
We use calibration standards that are at least four times more accurate than the instrument we are calibrating, resulting in a 4:1 test accuracy ratio (TAR). In the rare event that a 4:1 TAR is not attainable, we calculate and report the actual TAR in the comments section of the calibration certificate.
Adjustments
If an instrument fails the as-found calibration, we automatically attempt to adjust it so that it passes the as-left calibration.
In the event that an instrument passes the as-found calibration, yet is close to failing, then we will also attempt to adjust the instrument. We define “close” as when the deviation between the instrument and our calibration standard for any individual test point is greater than 75% of the instrument’s accuracy.
Certificates
We perform a quality review of all calibration certificates prior to submitting them to our customers. Certificates are submitted to customers as PDF documents. We enable customers to access and print their certificates 24/7 through an easy-to-use interface on our website. View demo here
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