The equipment that is needed for performing temperature sensors’ thermal calibration largely depends upon the desirable accuracy as well as easiness of usage. The larger is the precision needed, the more demanding is the procedure as well as the costs. The equipments for Calibration Systems is usually divided into 1 of the 3 groups.
- The general purpose system used to test temperature sensors in industrial plants generally provides an accuracy of 1.0 degree Celsius to 0.1 degree Celsius making use of the comparison techniques.
- A secondary standard system used for high-quality comparisons as well as fixed-point measurement typically provides an accuracy of 0.1 degree Celsius and 0.01 degree Celsius.
- The primary standardization system makes use of the highly advanced & precise equipment for achieving accuracy better than 0.001 degree Celsius.
Typical equipments utilized for comparison calibration include the following:
- A standard PRT or the secondary PRT
- Multiple temperature baths
- System for data acquisition
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Temperature Sensors
For low temperature calibration, Platinum resistance detectors are utilized as SPRT & RTD forms, which are quite stable as well as highly accurate. A noble-metal thermocouple, such as an R, S type, is utilized for high temperature calibration. Such sensors should have accuracy & repeatability.
Standard PRT
SPRT or Standard-Platinum-Resistance-Thermometer happens to be a highly accurate standard that is currently available, but it is also quite an expensive one, & other such standards are the better acceptable alternatives as per the temperature ranges covered, desired accuracies, capability , or calibration lab preferences.
Secondary SPRTs
These are much more usable & deal with less processing interferences. It is cheaper than SPRT.
Master Thermocouples
These are utilized as reference sensors in the comparison calibration processes. These are placed together with the calibrated sensor in quite a stable temperature zone, and their values are compared & errors are calculated.
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Temperature Reading Methods
These devices measure the power of sensors; they should be having higher resolution as well as fine accuracy.
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Secondary Temperature Sources
Dry Block Calibrator
This provides a highly convenient portable device for monitoring industrial sensors & typically achieves relatively fast heating and cooling.
Stirred Liquid Bath
Such a bath provides an excellent thermal environment for probe immersion because there’s no air gap between probe & medium.
Ice Baths
Such a bath consists of a mixture of melting shaved ice & water.
Negative Baths
Negative Bath & Ice Bath are primarily utilized for RTD calibration, providing negative temperature for the application of lower temperature calibration.
Fluidized Calibration Bath
Such a bath is a unique way to obtain precisely controlled temperatures.
Coefficient of Uncertainty
In the past, test device error or inaccuracy was usually a concern when the test device was used as a reference. The concept of uncertainty is now often used in the calibration of precision instruments, where high precision is required in the measurement. This concept is viewed based on several significant parameters. Today, calibration labs must calculate & add total/expanded uncertainty to all measurements while calibrating test instruments. This should be noted that “error” isn’t “uncertainty”.
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