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[January 2002]
New Family of Temperature Calibrators from Isotech
Offer High Accuracy and Ease of Use
A new family of high-accuracy dry-block temperature calibration systems,
designed for use in industrial, scientific and commercial environments, has
been announced by Isothermal Technology Limited (Isotech). The PLUS family
of portable and bench-top systems all use a sophisticated arrangement of
high accuracy plug-in temperature controllers and indicators to ensure
maximum accuracy, reliability and ease of use.There are nine PLUS models, covering different temperature ranges from -55°C
to +1200°C, temperature bath volumes and mechanical configurations. Each
model is available in two variants, a Basic (B) version and a Site (S)
version. B versions incorporate one sophisticated temperature controller
with a dual display for Set Temperature and Dry Block Temperature, whilst S
types additionally include a built-in digital indicator to which an external
temperature sensor can be connected. The control and indication system for
the PLUS family was developed with the support of Eurotherm Limited, a world
leader in industrial and process control systemsDuring normal calibration routines, the unit under test may simply be
compared to the displayed controller value, but for higher accuracy Isotech
recommends the use of an external probe connected to the additional
indicator of the S model. This approach, which compensates for temperature
gradient and loading errors, gives greater accuracy and traceability,
meeting the requirements of ISO 9000 and other recognised quality standards.All S types feature a universal sensor input, allowing Platinum Resistance
Thermometers, Thermocouples (Types K, N, R, S, L, B, PL2, T, J and E) along
with Linear Process Inputs (including 4-20mA current transmitters) to be
displayed on the inbuilt indicator. The indicator can be programmed with up
to five calibration points to provide high accuracy digital probe matching.
Both indicator and controller - based on a standard Eurotherm Model 2216
controller -are addressable over a serial communications link.All PLUS models include a PC Interface and a software tool, Cal NotePad,
designed for use with MS Windows. Increased resolution of ±0.01 is available
throughout the range via the PC interface and from -19.99 to +99.99 locally
on the auto-ranging front display. The controllers features multi-point
block to display correction giving good absolute accuracy.Achieving Traceable Results with Dry Block Calibrators
It is accepted best practice that a previously calibrated probe is placed
into the Dry Block calibrator insert along with the thermometer under test.
In this way, measurements can be related to appropriate standards, generally
international or national standards, through an unbroken chain of
comparisons. This approach meets the requirements of many international
quality systems, including those of ISO 9000.Merely using the Dry Block alone as a standard raises issues regarding
traceability and uncertainty. Unfortunately, there are a number of poor
designs currently being marketed where it is difficult to calculate the Dry
Block uncertainty in a satisfactory manner.Recently, International Guidelines have been published by the EA (European
Cooperation for Accreditation) that give guidance, and requirements, for the
calibration of Dry Blocks (EA10-13). For the most demanding applications
Isotech continue to recommend that a reference probe is used, the same
method as used in secondary temperature laboratories. However, for less
demanding calibration, and quick testing of sensors, the Dry Block can be
used without a reference probe. This is the underlying application
difference between PLUS B and PLUS S models.
ENDS