All thermometers are standardized, but not all thermometers are calibrated.
In order to manufacture a thermometer, the instrument must be compared to a traceable reference standard. Standardization during manufacturing establishes the guidelines for line and number placement on the glass, thus the thermometer has been standardized.
If a thermometer is calibrated (in the past the term certified may have been used) this means that after the instrument is manufactured, it is compared to a instrument that was certified by an outside body at a specific point or points along the scale. The results of this calibration are recorded on an official report. This report of calibration accompanies the calibrated instrument after the calibration process.
What is the difference between a Traceability Certificate and a Calibration Report?
Enviro-Safe, Easy-Read, Double-Safe and FRIO-Temp thermometers are supplied with a traceability certificate. This statement is your recorded assurance that the instrument you received was manufactured by comparison to a measurement instrument, standardized to a national standard (NIST), with an identified, unbroken chain of measurement uncertainty.
The accuracy stated is the allowable tolerance, or maximum error, acceptable with a particular instrument in relation to the “true” value. This is normally stated as a value, plus or minus. For example, if a thermometer has a ±1º maximum scale error it means that at any given point on the scale, the instrument could read up to one degree above, or one degree below the test point. At 20º centigrade, a thermometer may read up to 21ºC or down to 19ºC and still meet accuracy requirements.
A calibration report records the calibration of an instrument. Calibration of an instrument requires completion of a three step process:
1) Comparison of an instrument to a standard.
2) Documentation of the standard’s traceability to the national standard in SI units accompanied by an unbroken chain of identified uncertainty.
3) Statement of the variance of the instrument from the standard in specific measurements.
Calibration essentially verifies that an instrument meets stated accuracy and further gives specific correction values in order to use the instrument precisely in an application. This is also known as “measurement traceability.”
Most thermometers have a traceability certificate, but only calibrated thermometers have calibration reports.