Automated Public Health Controllers

 These systems are used for time and temperature control of HTST systems. There are concerns that with sequential control, the critical control points (CCP's) are not monitored all the time; if during the sequence it got held up, the CCP's would not be monitored. With operator control, changes can be made to the program which might affect CCP's; the system is not easily sealed. No computer program can be written completely error free in large systems; as complexity increases, so too do errors.

This gives rise to a need for specific regulations or computer controlled CCP's of public health significance:

  1. dedicated computer - no other assignments, monitor all CCP's at least once/sec
  2. not under control of any other computer system or override system, i.e., network
  3. separate computer on each pasteurizer
  4. I/O bus for outputs only, to other computers no inputs from other computers
  5. on loss of power - public health computers should revert to fail safe position (e.g. divert)
  6. last state switches during power up must be fail safe position
  7. programs in ROM - tapes/disks not acceptable
  8. inputs must be sealed, modem must be sealed, program sealed
  9. no operator override switches
  10. proper calibration procedure during that printing - Public health computer must not leave public health control for > 1 sec and upon return must complete 1 full cycle before returning to printing
  11. FDV position must be monitored and temperature in holding tube recorded during change in FDV position
  12. download from ROM to RAM upon startup
  13. integrated with CIP computer which can be programmed e.g., FDV, booster pump controllable by CIP computer when in CIP made only