Emerson Rosemount 3490 Series, Reference Manual

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Table 4-21: Custom Mode Relay Parameters
Parameter Description Factory default
P250 Start On Relay energizes when the selected condition is true.
See also
Table 4-22 .
None
P251 Stop On Relay de-energizes when the selected condition is
true. See also
Table 4-22 .
None
P252 Stop If Relay de-energizes when the selected condition is
true. See also
Table 4-22 . P252 is a fail-safe for P251.
None
P253 Start Time This defines the clock time for when a Custom mode
relay operation will begin (if P250 = Time) or end (if
P251 = Time). “7:00” - i.e. 7AM
P254 Interval This is for defining the interval for repeating a
Custom mode relay operation.
P255 and P256 are for setting up a second starting
time and an associated interval. “1:00” i.e. 1hr
0min
P257 Max Retries This defines the maximum number of failed
attempts to perform Custom mode relay operations
before it is deemed an alarm condition.
The alarm condition can happen if the control unit is
in Program mode, which prevents all Custom mode
relay operations from starting. Also, it can happen
when the maximum time for an energized relay has
been reached and is preventing a Custom mode
relay operation from completing. 10
Table 4-22: P250/P251/P252 Options
Options Purpose of option Start on
(P250) Stop on
(P251) Stop if
(P252)
None Switched off. Yes Yes Yes
Time P253 and P254 determine when a Custom
mode relay is to be energized. Yes Yes N/A
PV > Level Energize a Custom mode relay when the
control unit PV value (D800) is greater
than the relay On Point. Yes N/A N/A
PV < Level De-energize a Custom mode relay when
the control unit PV value (D800) less than
the relay On point. N/A Yes Yes
Ext Trig
(1)(2)
Energize a Custom mode relay when a
digital input is active. Yes Yes Yes
Ext Trig Xs
(1)(2)
When a Digital Input is active, de-energize
a Custom mode relay after X seconds
delay. N/A N/A Yes
(1) This does not require Digital Input IN1 or IN2 to be allocated an action.
(2) Abbreviations: “Ext Trig” = External Trigger (Digital Input).
Reference Manual Getting started
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