Dairy processing: Aseptic processing and packaging systems
Indicating thermometer

The indicating thermometer provides the official processing temperature of the product, which is a critical factor in the scheduled process.

General conditions

Is clean and in good operating condition
Is mercury actuated or equivalent, or a resistance temperature detector (RTD) of sufficient accuracy and precision
Mercury actuated or equivalent thermometers:
- have direct reading
- are contained in a corrosion resistant case which protects against breakage and permits easy observation of the column and scale
- have filling above the mercury that is nitrogen or an equally suitable gas
- have a bulb that is Corning normal or equally suitable thermometric glass
RTD type thermometers:
- are fail-safe using two separate RTDs
- are accurate and reliable
- meet the scale and thermometric response specifications (see Appendix J: Design criteria for digital thermometers for use in critical processes)

The indicating thermometer is located in the sensing chamber, along with the probe for the safety thermal limit recorder
- ensure the indicating thermometer probe is located after the probe for the safety thermal limit recorder
- verify the distance between the 2 probes is not be more than 30 cm (12 inches)
Ensure that the indicating thermometer is easily and safely accessible by the operator to allow accurate reading of the processing temperature

Scale graduations are in 0.5°C (1°F) divisions with not more than 9.4°C (17°F) per 25 mm (1 inch) of graduated scale
Ensure the stem fitting is pressure-tight against the inside wall of the fitting, with no threads exposed to product

Test the indicating thermometer for temperature accuracy and thermometric response upon installation and at an interval of at least every 6 months
- refer to Critical process test procedures - Thermometers
- follow-up on out of specification findings
Investigate the safety of any product produced with out of calibration equipment
- for example, if the indicating thermometer at the outlet of the holding tube is reading higher than the calibration standard, the product may have been under processed
Increase the frequency of testing if the calibration is consistently found to be out of adjustment
- if the calibration is consistently found to be out of adjustment, immediately identify and rectify the reason for the calibration problems
Keep records of tests performed to determine the thermometer's calibration

Seal the access to calibration adjustments once the thermometer has been calibrated
- attach the seal to the cover or scale plate on mercury in glass (MiG) thermometers
- seal the thermometer panel and the RTD sensor housing on resistance thermal devices