Testing Methods

Unfortunately, not all calibrations are equal, and not all instruments require the same type or level of testing to verify that they are fit-for-purpose and performing within expected accuracy. Due to this, we are strong advocates for transparency in testing methods used by all calibration laboratories, and ensuring that laboratories have a capability that is suitable for confirming the performance of instruments prior to accepting them for calibration.  Recent changes to ISO/IEC 17025 have thankfully placed increase requirements on calibration laboratories so that they must now disclose or negotiate with end user about testing methods used, accuracy requirements, and their ability to assess the instruments compliance to the accuracy specification.

At APL we extensively use the Metrology Society of Australasia Test Methods for Pressure (MSA Test Methods 1 & 2), which clearly outline the testing requirements, the need to determine an accuracy specification, and rules on determining compliance.  For some specialised instruments that are not within the scope of the MSA Test Methods, we use other published methods such as Euramet CG-3 for Dead Weight Testers and ISO3567 for vacuum calibrations using our Vacuum Comparison System (VCS).  For electrical instruments, it is more common for calibration regimes to be prescribed by manufacturers, which we utilise in combination with our own internally developed method which has been guided by Euramet CG-15.

Does it comply?

It is not always easy to understand all technical information presented in calibration reports.  For industrial instruments, often the user is primarily interested to know if the instuments performs within the original specification defined by the manufacturer, and therefore we believe it is important for trained and quaified staff in calibration laboratories to make this determination and present it clearly for the user.  Determining whether an instrument has or has not performed within specification is not always as easy as comparing the size or error/correction with the accuracy specification, as there is naturally some uncertainty in the error/correction.  ISO/IEC 17025 requires come consideration of uncertainty in determining compliance, and more detailed guidance on valid approaches is provided by ILAC

At APL, we adopt the following practices by default (users are welcome to specify their own criteria if they prefer):

Instrument Type Test Method Accuracy Specification Compliance Decision Rule
Mechanical pressure instruments MSA Test Method 2 Manufacturer's specification or based on dial size as defined in MSA Test Method 2 Neither of corrections or uncertainty can be greater than accuracy specification at any point and reference uncertainty must be within limits as defined by MSA Test Method 2.
Digital pressure instruments MSA Test Method 1 Manufacturer's specification The sum of |correction| + uncertainty must not be greater than accuracy specification at any point 
Digital electrical instruments APL internal method in accordance with Euramet CG-15 Manufacturer's specification The sum of |correction| + uncertainty must not be greater than accuracy specification at any point 

Medium/high vacuum gauges 

(Pirani & CDG)

ISO3567 None used (unless requested) No compliance statement provided unless requested. These are specialised devices, often tested over limited ranges to suit specific applications. We can discuss any specific accuracy requirements on a case-by-case basis if a compliance statement is required.
Dead Weight Testers APL internal method in accordance with Euramet CG-3 None used  No compliance statement provided.  These are specialised reference devices and their performance is highly dependant on local environmental factors.  We will provide a statement of uncertainty and generated pressure envelopes at some assumed or user-specified conditions.

 

In all cases, we are very happy to discuss any specific requirements users may have for accuracy, decision rules, uncertainty, tested points or test conditions, so feel free to discuss your requirements with us prior to calibratoin.