Hach-Lange SI792(x) E HACH GLI 3700 series SI792(x) T 7MA2200 and 8398 series User Manual - Manual (Page 93)

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To avoid or limit consequential damage, it is therefore recommended to
design the control loop such that a malfunction in an instrument results
in an automatic change over to the backup control system; this is the
safest operating state for the environment and the process.