ILAC-G24 Edition 2007 (E)

1. By Dr. Mohamed Shaltout
+201270000612 P A G E
01
ILAC-G24 Edition 2007 (E)
OIML D 10 Edition 2007 (E)
Guidelines for the determination of calibration
intervals of measuring instruments

2. Introduction

3. 6.4.6 Measuring equipment shall be calibrated when:
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calibration of the equipment is required
to establish the metrological traceability
of the reported results.
The measurement accuracy or
measurement uncertainty affects the
validity of the reported results, and/or
01
02

4. 6.4.7 The laboratory shall establish a
calibration programme, which shall
be reviewed and adjusted as
necessary in order to maintain
confidence in the status of
calibration.

5. ILAC-G24 Edition 2007 (E), OIML D 10Edition 2007 (E)
(2) It is also the responsibility of the laboratory
to evaluate the effectiveness of the method it
chooses to implement.
It is the responsibility of each individual
laboratory to choose any of calibration
methods intervals determination based on its
individual needs and its individual assessment
of risks
(1)

6. Distinguish the equipment that it has been calibrated
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A calibration certificate or calibration label shall
not contain any recommendation on the
calibration interval, except where this has been
agreed with the customer.
6.4.8
7.8.4.3
All equipment requiring calibration or which has a
defined period of validity shall be labelled, coded
or otherwise identified to allow the user of the
equipment to readily identify the status of
calibration or period of validity.

7. “When to do it” and
“How often to do it”
“ “

8. “When to do it” and “How often to do it”
Uncertainty Of
Measurement
Required
Risk Of A Measuring
Instrument
Exceeding The Limits
Cost Of Necessary
Correction Measures
Methods Used
Outside Their
Intended Scope
Type Of Instrument
To be continue,,,,,,,

9. “When to do it” and “How often to do it”
Tendency To Wear
And Drift
Manufacturer’s
Recommendation;
Extent And Severity
Of Use
Environmental
Conditions
To be continue,,,,,,,

10. “When to do it” and “How often to do it”
Recorded History Of
Maintenance And
Servicing
Frequency Of Cross-
checking Against
Other Reference
Standards Or
Measuring Devices
Frequency And
Quality Of
Intermediate Checks
In The Meantime
Transportation
Arrangements And
Risk

11. Methods to determine calibration intervals
(1) The Automatic
adjustment or
“staircase”
(calendar-time)
(5) Other statistical
approaches
(4) In service checking,
or “black-box” testing
non-calendar time)
(2) Control chart (calendar-
time)
(3) “In-use” time (non-calendar
time)

12. Method 1: Automatic adjustment or “staircase” (calendar-time)
Each time an instrument is calibrated on
a routine basis, the subsequent interval
is extended if it is found to be within
e.g., 50 % of the maximum permissible
criteria that is required for
measurement, or reduced if it is found
to be outside this maximum permissible
criteria

13. Method 1: Automatic adjustment or “staircase” (calendar-time)
Advantages
1. This produce used to rapid adjustment of intervals
and is easily carried out without rewrite calibration
program effort
2. All laboratory equipment will not be stopped until
calibration is done simultaneously as before.
disadvantage
1. Double effort on the lab to determine the condition
of each individual device

14. Method 1: Automatic adjustment or “staircase” (calendar-time)
disadvantage
2. Treating instruments individually may be that it is
difficult to keep the calibration workload smooth and
balanced and calibration programme will taken much
efforts.

15. Method 2: Control chart (calendar-time)
1. Calibration points are chosen and the results are
plotted against time.
2. Both dispersion of results and drift are calculated
(precision (SD) and accuracy(mean))
3. The drift (mean) being either the mean of drifts
over one calibration interval, or in the case of very
stable instruments, the mean of drifts over several
intervals
4. Compare the obtained results with manufactures
acceptance criteria

16. Method 2: Control chart (calendar-time)
Advantages
1. Calculation of the dispersion of results will indicate
whether the manufacturer’s specification limits are
met
2. Analysis of drift found may help in indicating the
cause of drift.

17. Method 2: Control chart (calendar-time)
disadvantage
1. Before use this method, knowledge of the law of
variability of the instrument, or similar instruments,
is required
2. Difficult to achieve a balanced workload

18. Method 3: “In-use” time
Calibration interval is expressed in hours of use, rather
than calendar months
Advantages
1. The advantage of this method is that the number of
calibrations performed and therefore the cost of
calibration varies directly with the length of time
that the instrument is used

19. Method 3: “In-use” time
Disadvantages
1. The initial cost of the provision and installation of
suitable timers is high, and since users may
interfere with them
2. Difficult to achieve a smooth flow of work

20. Method 4: In service checking, or “black-box” testing
1. Critical parameters are checked frequently (once a
day or even more often) by portable calibration
gear, or preferably, by a “black box” made up
specifically to check the selected parameters
2. If the instrument is found to be outside the
maximum permissible error by the “black box”, it is
returned for maintenance and full calibration.

21. Method 4: In service checking, or “black-box” testing
Advantages
• Not all laboratory equipment goes out
simultaneously for calibration
• Continue to monitor the calibration status of the
laboratory's instruments
Disadvantages
• Double effort on laboratory staff

22. Method 5: Other statistical approaches
1. Methods based on statistical analysis of an
individual instrument or instrument type can also
be a possible approach
2. When large numbers of identical instruments (i.e.
groups of instruments) are to be calibrated, the
calibration intervals can be reviewed with the help
of statistical methods

23. Method comparison
• No one method is ideally suited for the full range of
instruments encountered
• Method chosen will be affected by whether the
laboratory intends to introduce planned maintenance

24. Method comparison