Furnaces,Ovens,Melting Furnaces,Laboratory Incubators,Laboratory Chambers,Laboratory Bath,Autoclaves,Orbital Shaker,Hot Plate andMantles,Tinning Pot/Lead Bath,Process Control Instruments,Digital Controllers,Digital Indicators,Transmitters,Digital Energy Meters,Digital Timers & Counters,Data Logger,Electric Heaters,Thermocouples,Rtd Sensors Calibration
The Calibration Guide outlines the basic technical requirements for laboratories undertaking calibration of enclosures controlling temperature and/or humidity in their working volume. It aims to harmonize calibration practices applied in the calibration of the enclosures to obtain reliable and widely recognized calibration results. The guide is also recommended for Accreditation Bodies when accrediting laboratories for the calibration of temperature and/or humidity controlled enclosures.
furnaces, ovens, laboratory incubators, chambers, baths,
autoclaves, orbital shakers, hot plates, mantles, tinning pots/lead baths,
process control instruments, data loggers, electric heaters, thermocouples, RTD
sensors, and various other equipment. It also mentions various industrial
ovens, such as hot air, stainless steel, vacuum, and plastic-pre-heating ovens.
The summary also mentions various types of melting furnaces, such as aluminum,
lead, gold, and silver, and various types of incubators, such as COPP, BOD, dry
bath, and environmental chambers. The summary also mentions various water
baths, such as 6 and 12 hole water baths, constant temperature water baths,
recirculating water chillers, and oil baths.
The calibration of a temperature and/or humidity controlled
enclosure in principle is the determination of the deviation between the
indication on the display values of the enclosure and the corresponding values
measured in the enclosure. The calibration of other parameters like air
temperature/humidity spatial distribution in the specified calibration volume,
air temperature/humidity temporal stability over a representative period of
time, thermal inertia, recovery time, etc. can also be specified in the calibration
scope of a laboratory.
However, the calibration of the indication of an enclosure
is not the best method for documenting the environmental condition during the
operation of an enclosure. The use of at least one sensor for temperature
and/or humidity in close proximity with the load in the enclosure usually
provides much more reliable data than the indication of the enclosure.
Calibration laboratories should inform their customers about this fact,
preferably before signing the contract with the customer.
To reduce costs, a customer may ask for a calibration at a
single measurement point at one location in the enclosure (one point
calibration). However, mostly calibration should be more extensive to meet the
requirements of the customer’s activities with the enclosure. It is highly
important to clearly state the coverage of the calibration in the corresponding
calibration certificate.
Laboratory and customer must agree the scope of the
calibration requested, duration of the test, parameters to be determined,
loading conditions, etc. These calibration conditions have to be recorded by
the laboratory. It is strongly recommended that if an enclosure is
characterized for the first time or modified that it should be
calibrated/characterised with both an empty and a loaded chamber.
The calibration of an enclosure is a crucial aspect of
laboratory calibrations, and it is essential to specify the criteria for
accepting an enclosure to be calibrated. These criteria should include the
volume of measurement in the enclosure, control system of measurement
parameters, and technical documentation of the enclosure. Reference to
technical guidelines is recommended, but the usual calibration of thermally
and/or humidity controlled enclosures is restricted to enclosures operated at
normal pressure.
The calibration of an enclosure requires at least the
determination of several parameters, which will be considered in the
uncertainty budget: air temperature/humidity spatial distribution in the
specified calibration volume, air temperature/humidity temporal stability over
a representative period of time, uncertainties associated with the working
standard used for the calibration, radiation effect associated with the
emissivity of the temperature sensor and sensor dimension, time-dependent
temperature differences between air, measuring probe(s), and load in the
enclosure, sensitivity to temperature changes with probes placed in air or in a
buffer (liquid, block), influence of loading of the enclosure to the spatial
distribution and temporal stability of air temperature and humidity, influence
of ambient conditions, and resolution of indicators.
The scope declared by a laboratory for calibrations of
enclosures should state the parameters of the enclosure, such as air
temperature in an empty working-volume, air temperature in a loaded
working-volume, air humidity in an empty working-volume, air temperature at a
single spot in the enclosure, and specify measurement of probe in air or buffer
(liquid, block).
In addition to ISO/IEC 17025 requirements, reports related
to the calibration of an enclosure must include details of the working
condition parameters of the enclosure used during the calibration, specific
volume calibrated and distribution of the sensors, characteristics of the
loading, and if the results of the sensors are used to determine other
parameters, such as temperature/humidity spatial distribution or
temperature/humidity temporal stability, defining the parameter and its
calculation.
Proficiency testing is crucial for calibration laboratories
to ensure their competence through proficiency tests and intercomparisons.
Acclimatization of enclosures is typically conducted in the customer's
premises, excluding initial calibration at the manufacturer. It is recommended
to use a well-characterized enclosure in an independent institute for
proficiency testing. Internal comparisons can help control the performance of
different calibrators within a laboratory.
The calibration certificate for temperature and humidity
controlled enclosures is valid only for the air temperature and humidity in the
empty useful volume of the enclosure. Under ambient conditions, considerable
deviations from the calibration value can be considered. It is strongly
recommended to install temperature and/or humidity sensors in close contact to
the load in the enclosure, as these sensors provide more realistic data on the
condition in the enclosure than the indication of the calibrated enclosure.
Radiation effects can affect measurements in climatic
chambers, as the temperature of the walls of many models is lower than that of
the air due to radiation losses. The temperature of the thermometer and an
object in the enclosure can differ considerably, especially if the emissivity
or emittance (e) of the object differs from that of the thermometer. The
influence of this effect increases over proportionally at higher temperatures,
while below room temperature, the effect is inverse but often negligible.
Objects in the useful volume will generally not assume the
air temperature prevailing during calibration due to loading conditions,
position, size, and material not conforming with the thermometer used for the
calibration of the enclosure. Relative humidity distribution in the useful
volume may change significantly if there are water vapour sources or sinks,
effective mixing of the useful volume, or leaks leading to air exchange with
the environment.
Measurement uncertainty is valid only if the measurement
conditions documented in the specific case are complied with. The remaining
radiation effect of the standard used, related to the enclosure calibrated
here, was determined and allowed for in the measurement uncertainty.