Calibration Management
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Intermediate Check Guide: How to Maintain Confidence in Your Reference Standards Over Time
by EDSPONCE with 86 COMMENTS
I received a comment regarding what to do about the “high readings of environmental conditions”
(temperature and humidity) that they are experiencing during their onsite or field calibration
compared to their defined specs when inside the lab. He is worried that an auditor may find an issue
once it is displayed in their calibration certificate.
I believe this is also a concern to some or most Calibration Techs that perform calibration outside
their lab so it is worth a topic to discuss. This can become an audit issue if not properly addressed
since it is required to be displayed in the calibration certificate.
Also, one of the questions I received during an audit is, how do you ensure that the reference
standards you use outside the laboratory are still in confidence or in good condition once it left
and/or returned from the fieldwork?
In this post, I will share with you a quality control procedure that we can easily execute to ensure
confidence in your reference standard before or after it is used outside the calibration laboratory.
This is what we call an Intermediate Check.
I will also share in this article the related clauses under ISO 17025:2017 and ISO 9001:2015 where
intermediate checks are a requirement. Once we performed Intermediate checks, we will be
confident that we have fulfilled these clauses..
This is a must to detect any possible issue that can be faced during or after an onsite calibration
work. This also applies to those instruments or reference standards that are sent out for 3rd party
calibration.
I will show to you the step-by-step procedure on how to implement this.
..
What is an Intermediate Check?
An Intermediate Check is a periodic quality check performed for every reference standard while it is
still within calibration date to ensure that is still in good condition.
pressure gauge adjustment and verification technique-actual demonstration
Good condition means that the error or drift that it encounters is within acceptable limits within a
given period or given situation for example, after being used outside the laboratory.
Me during my on-site job exposed to a 46.9 deg C environment
During my on-site job exposed to a 46.9 deg C environment
Intermediate Check is one type of calibration quality control that is implemented internally where
the resulting data should be recorded and analyzed. This is a planned activity where the frequency
of implementation should be laid out.
Intermediate check may include ‘functionality check’, because this is literally what you do, to check
and verify the functionality of the reference standard in combination with the measurement results.
There are many ways to perform an Intermediate check, but the simplest is performed by comparing
two instruments with the same parameters, one is a standard and the other is a UUC (Unit Under
Calibration) to check for any differences or unacceptable errors.
With this method, Intermediate Check can be called Verification.
There are many applications for intermediate checks inside a lab or in many technical operations
involving equipment. One specific application is for the reference standards that are used during a
field or on-site calibration, which is the focus of this post.
Another application for an intermediate check is during preventive maintenance.
Since we will be focusing on reference standards that are used outside the lab, the frequency is
every time it is being used outside the lab. This can fall under a work instruction for all reference
standards that will be brought outside the facility.
This is applicable whether the standard is for 3rd party calibration or simply performing an onsite or
field calibration.
This is just a simple cross-check so there is no need to perform a full range check or calculation of
measurement uncertainty. The important thing is to have a program or procedure that is
implemented and documented.
It is just a simple way to detect any out-of-specs reading that may have resulted during exposure to
a different environment or strong vibrations or even mishandling outside the lab.
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Why Do We Need to Implement Intermediate Check?
In addition to the reasons above on why we need to perform intermediate checks, another reason is
Intermediate checks are required by Standards, specifically the ISO 17025 and ISO 9001 Standards.
This means that an Intermediate Check procedure should be implemented.
Below are the Intermediate Check-related clauses for ISO 17025:2017:
Clause 6.4.2: When the laboratory uses equipment outside its permanent control, it shall ensure that
the requirements for equipment of this document are met.
under clause 6.4.10, which states that: When intermediate checks are necessary to maintain
confidence in the performance of the equipment, these checks shall be carried out according to a
procedure.
under Ensuring the Validity of Results, clause 7.7.1 The laboratory shall have a procedure for
monitoring the validity of results. This monitoring shall be planned and reviewed and shall include,
where appropriate, but not be limited to: (e). intermediate checks on measuring equipment;
Below are the Intermediate Check-related clauses for ISO 9001:2015: Under Clause 7.1.5:
Monitoring and measuring resources.
7.1.5.1 General
The organization shall ensure that the resources provided:
b) are maintained to ensure their continuing fitness for their purpose.
The organization shall retain appropriate documented information as evidence of fitness for purpose
of the monitoring and measurement resources.
.
The following are the main points why we should perform Intermediate Check based on these
Standards:
We need to perform an Intermediate Check for our reference standards if these standards are used
outside of our permanent control.>> Exposure to a different environment when brought outside the
lab.
Necessary to maintain the confidence of our reference standards >> performed in a scheduled
interval (every 3 months) for example during Preventive maintenance to verify measurement output.
To monitor the validity of results. This means that, after many usages, to ensure that it is still in
confidence while we are waiting for its next calibration due date, we will verify if the measurement
results are still within the acceptable range, this will show us immediately if a drift already occurs.
No need to wait for the next recalibration period.
We perform Intermediate checks to ensure continuing fitness for its purpose, which has the same
meaning as number 3.
.
Records of Intermediate Check is one of the pieces of evidence that shows we continuously monitor
our reference standards for their fitness of purpose throughout its calibration period.
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How to Verify the Environmental Specs of Your Reference Standard?
UUT specs
Verify the environmental specifications of the reference standards in its manual to ensure it is suited
to the environment that you will be exposed to.
Once this intermediate check has been performed, regardless of what temperature or humidity the
reference standard has been exposed to you are confident that the calibration you performed outside
of your lab is not compromised.
But before exposing your reference standard to a different, more harsh environment, make sure to
check first its environmental specifications in its user manual to ensure that the reference standards
are designed for that range of environmental conditions to avoid damage.
Also, in order to support the validity of the procedure even if the environmental conditions are
different compared when inside the lab, the below information should be reflected in your
calibration record/report:
The term “on-site” calibration – it is expected that a procedure with regards to onsite calibration is
in place in your documentation. This is to differentiate it from the calibration performed inside the
lab (bench calibration)
Customer approval of the procedure performed– show evidence of customer or user approval.
As part of our quality control, we should consider or implement how we ensure that our reference
standards are still ok while it is being exposed to a harsh environment that can somehow affect its
performance, like:
very high temperatures,
very high humidity
strong vibrations
contaminants
The procedure is to have another reference standard that we can use to compare and take a reading.
Both should have a valid calibration status. It is the same as calibrating a simple UUT (Unit Under
Test) with a reference standard but it does not necessarily a more accurate standard.
As long as we can detect and verify the desired test point then it is ok. But of course, a higher level
standard is better if we have it.
A simple Functionality Check for the RTD using a metrology well.
An example of an Intermediate Check for the RTD using metrology well.
One example is an RTD and a Metrology Well. The Metrology Well can be used as a reference
standard in performing a functional check with the RTD. It does not necessarily a more accurate
standard. I hope you got my point.
Another example of performing an intermediate check is by using the same reference standard to be
compared to a previously calibrated UUT. The UUT is designed for this purpose. See if they have
the same or acceptable readings or results comparing it with the previous record.
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7 Steps to Perform an Intermediate Check- SOP for Intermediate Check
In performing an intermediate check, below are the steps I recommend and follow as an SOP:
The same as performing a calibration, all reference standards that will undergo an intermediate
check should be left to stabilize in the lab for at least 1 hour.
You should prepare a checklist or a form to document and list the needed details about the
intermediate check. Below are some details to include (and anything that is significant during
checking):
The identification of the Reference standard to be used for cross-checking.
The name of the standard that will undergo intermediate check,
Brand
Model
Serial No.
Temperature and humidity
Date of functionality check when released
Date of functionality check when returned
Who performed the functionality Check?
The physical conditions including accessories
The tolerance to determine pass and fail status.
Choose a test point for the intermediate check as per available functions or nominal value.
For example: In an RTD, you can check only at 0 deg C and 100 deg C test points for a 0 to 200
range
For a Test Gauge, check only on its mid-range (50%
of full scale)
Perform at least 3 trials.
Analyze the result. One way is to compute the error and determine the acceptance criteria. See more
below
Have it approved by an authorized person then it is ready for field work.
Then once the reference standard has returned to the lab, repeat steps 2 to 5. And you’re done..
What is the Acceptance Criteria Used to Verify Intermediate Checks Results?
There is no fixed rule to follow when it comes to what acceptance criteria to be used during the
intermediate checks to determine a pass or failed result.
There are so many instruments with unique properties that need different methods of assessment.
Because of this, it is important to document the chosen method as part of your records for
standardization and audit purposes.
How to check the Intermediate check results? After you have gathered your data, below are some
ways where you can come up with your acceptance criteria to check or verify the intermediate
check results:
Determine the error and compare it with the manufacturer’s specifications for accuracy or tolerance
details. This is the simplest that I used. How to determine the error? See this link>> 3 ways to
verify the measurement results in a calibration certificate
Determine the drift and use the limits of the control charts up to 3 standard deviations. You can use
the data during the analysis of the calibration interval.
Use other guides where a tolerance limit is provided for specific instruments like OIML or ISO
guides.
Conclusion
Intermediate checks are part of a laboratory quality control procedure. This can be used as evidence
of a good performance of a reference standard even if you use it outside the defined specs of the lab
with respect to bench calibration.
This is how we can demonstrate the validity of results if ever you will be audited regarding the
uncontrolled outside environment that the reference standard is exposed to.
I have discussed in this post the meaning of an Intermediate check, which is also a part of the
functionality check process.
I also discussed the importance of an intermediate check as part of a calibration program under
quality control, which is a requirement of ISO 17025 and ISO 9001, including a simple intermediate
check procedure with important details to be reflected in your report.
Do you have other means of quality control that you perform during a field or onsite calibration for
your reference standard? Please comment below.
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