Dairy Establishment Inspection Manual – Chapter 19 Appendices
Appendix 13 Design Requirements for Digital Thermometers for Use in Critical Processes (HTST, batch, HTST/ESL and UHT Processing Systems)

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The following criteria shall be used to evaluate resistance temperature devices (RTDs) for use as alternatives to mercury actuated direct reading indicating thermometers on pipelines in High Temperature, Short Time (HTST); Batch; Higher Heat, Shorter Time (HHST) or Extended Shelf Life (ESL); and Ultra High temperature (UHT) systems.

These criteria are:

  1. No more than 0.25°C (0.5°F) drift over 3 months use when compared to a certified source.
  2. Readout is displayed in units of temperature with a graduation of at least 0.1°C.
  3. Display changes at a rate that can be noted by the operator or responsible regulatory authority during the thermometric lag test.
  4. Self-diagnostic circuitry which provides constant monitoring of all sensing, input and conditioning circuits. The diagnostic circuitry should be capable of detecting "open circuits", "short circuits", poor connections and faulty components. Upon detection of failure of any component, the device shall blank or become unreadable.
  5. The effect of electrical noise shall be documented and available to responsible regulatory authority. Protocols for these tests shall be developed by vendors.
  6. The effect of high temperature and high humidity environment shall be documented. The device should show no effect after exposure to 38°C and 80% relative humidity for 7 days.
  7. Both probe and display case shall be constructed so that they may be sealed.
  8. Calibration of the device shall be protected against unauthorized changes.
  9. The device shall be protected against unauthorized component or sensing element replacement. Replacement of any component or sensing element shall be regarded as a replacement of the indicating thermometer and subject to all applicable tests identified under the CFIA's Critical Process Test Procedures.
  10. The sensing element shall be encased in appropriate material constructed in such a way that the final assembly meets Equipment Table 1 requirements of the Dairy Establishment Inspection Manual.

In addition, all parts of the DEIM inspection manual currently applicable to the indicating thermometer shall apply to any new device being proposed.

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