Rosemount 3491, Reference Manual, Page: 85 / 152

Reference Manual
00809-0100-4841, Rev. AA
May 2007
4-53
Rosemount 3490 Series
Energy Saving
(Special Control Function - see Table 4-12 on page 4-45)
P275 Engy Save Strt (Factory default is 0:00 h:m)
Set the time of day at which selected relays (P276) will energise until each
relay Off Point is reached. The energy saving start time is valid for one
minute; if missed by the 3490 Series Control Unit being off-line, no action is
taken when subsequently put back on-line.
P276 Engy Save RL (Factory default is 00000)
Select relays for the operation associated with parameter P275. Each digit
represents a relay. Relay RL1 is selected by editing the first digit to be a "1".
Similarly, relay RL5 is selected with the fifth digit. To de-select a relay, change
the appropriate digit back to a "0".
Scum line prevention (models 3491 and 3492 only)
(Special Control Function - see Table 4-12 on page 4-45)
P277 Scum line var (Factory default is 0.0)
This parameter defines the maximum overall variance in the programmed
On/Off point of selected relays (P278). The variance is in the units of the
On/Off point, spaced in 10 equal increments inside the On/Off points. Each
time the selected relays (P278) de-energise, the variance moves on an
increment.
P278 Scum line RL (Factory default is 00000)
Select relays for the operation associated with parameter P277. Each digit
represents a relay. Relay RL1 is selected by editing the first digit to be a "1".
Similarly, relay RL5 is selected with the fifth digit. To de-select a relay, change
the appropriate digit back to a "0".
Pump-down (Models 3491 and 3492 only)
(Special Control Function - see Table 4-12 on page 4-45)
Normally, when pumping out a wet-well, the lowest Off point ('pump off' level)
will be a fixed level above the Bottom Reference point. However, it is
sometimes required to make the pumps continue to run for a period past the
Off point or run down to the Bottom Reference Point. This will clear the sump
of sludge that may have collected at the bottom.
Assist Starts Rotation of 'leading' Assist relay is based on how many times it has
been energised compared to P271.
Assist On Time Rotation of 'leading' Assist relay is based on the hours that it has been
energised compared to P271.
Assist Ratio T For 2 Assist relays only - rotation based on the ratio of ON time for the
2 relays compared to P271.
(1)
Assist Ratio S For 2 Assist relays only - rotation based on the ratio of starts (times
energised) compared to P271.
(1)
Off, No rotation required.
(1) Ratio is based on the first two lowest numbered relays with the same mode.
Option Rotation basis