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Caution: In any critical application where failure could cause
expensive product loss or endanger personal safety, a redun-
dant limit controller is required.
The CN74000 Series allows Set Point 1 (and Set Point 2 is equipped) to operate as
limit or alarm type outputs. This function is available on all outputs except the pro-
portional current (output type 5). To enable a set point output to act as an alarm or
limit, Out1 (for SP1) or Out2 (for SP2, if equipped) should be set for OnOf.
When Out1 and / or Out2 are set to OnOF, then the alarm function menu items will
appear in the Secure Menu for the selected set point(s).
If the Alarm Programming code in the model number is set to 1, then set point 2 is
pre-programmed as an alarm. If the alarm Programming code in the model number
is set to 0 and the last number of the model number is not 0 then the second set
point is pre-programmed as a cooling output. This programming may be changed in
the field with the Factory Default procedure.
When setting SP2 value (S2t =AbS) or the ALLO and ALHi values (ALt = AbS) for
an absolute alarm, simply set the value at which the alarm is to occur.
When setting SP2 value (S2t = dE) or the ALLO and ALHi values (ALt = dE) for a
deviation alarm, set the difference in value from the Set Point 1 (SP1) desired. For
example if a low alarm is required to be 5 degrees below the SP1, then set SP2 or
ALLO to -5. If a high alarm is required 20 degrees above the SP1, then set SP2 or
ALHi to +20. If SP1 is changed, the alarm ( SP2, ALLO, ALHi) will continue to hold
the same relationship as originally set.
When Set Point Power Interrupt (S#Pi) or Alarm Power Interrupt (ALPi), is pro-
grammed ON and Set Point Reset (S#rE) or Alarm Reset (ALrE), is programmed for
Hold, the alarm will automatically reset after a power failure and on subsequent
power restoration if no alarm condition is present.
If Set Point Inhibit (S#iH) or Alarm Inhibit (ALiH), is selected ON, an alarm condition
is suspended upon power up until the process value passes through the alarm set
point once. Alarm inhibit can be restored as if a power up took place by pressing
both the INDEX and ENTER keys for 5 seconds.
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