A new family of high-accuracy dry-block temperature calibration systems, designed for use in industrial, scientific and commercial environments, has been launched by Isotech
The Plus family of portable and bench-top dry-block temperature calibration 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 -55C to +1200C, 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, while 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. During 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.
