Scope: This Guideline provides a method to check the calibration of Portable Electronic Thermometers (PET).
Frequency : 3 months.
PORTABLE ELECTRONIC THERMOMETER CALIBRATION PROCEDURE
PREPARATIONS:
Before initial use, and at least once a year thereafter, each portable electronic thermometer (PET) shall e re-standardized in a laboratory or other qualified calibration facility.
The PET shall be compared at three or more temperature points, near the midpoint and ends of the range; with either a National Institute of Technology (NIST) certified reference thermometer or an equivalent thermometer with accuracy traceable to the NIST.
The PET shall be calibrated in accordance with the manufacturer’s instructions.
Field Verification
Before each use or once per day (whichever is less frequent), PETS should be spot checked by comparing the ambient reading against an ASTM glass stem thermometer in liquid. If the reading differs by more than 0.25ºC (0.5ºF), the portable electronic thermometer should be re-standardized before it is used for custody transfer.
Verify that the certificates for the test equipment are valid. Check that the test equipment serial numbers and certification dates are accurately recorded on the test sheet and correspond with the test equipment used. Ensure the instrument tag and serial numbers are recorded on the test sheet.
CALIBRATION EQUIPMENT:
A) NIST certified reference thermometer
PROCEDURE:
On a monthly schedule, the portable electronic thermometer should be checked at two or more temperatures near the ends of its range against a NIST-certified reference thermometer or an equivalent thermometer with accuracy traceable to the NIST. Make this check by either:
a. Placing the two thermometers side-by-side in a circulating bath and leaving them undisturbed for at least 10 minutes before making the comparative readings, or
b. Placing the thermometer in a metal block temperature generator that has been verified against a NIST-certified reference thermometer. Alternatively, the ice point and boiling point of fresh water may be used for the accuracy check. The boiling point of fresh water must be corrected for altitude.
In addition the following physical checks should be made:
a. The junction between the cable and the probe should be checked for mechanical damage.
b. The cable insulation should be checked for cuts, breaks, or brasion.
c. Grounding cable should be checked for damage.
d. Case body should be checked for cracks or damage. If any of the damage above is noted, the PET shall be removed from service until repaired.