Emerson Rosemount 3490 Series Reference Manual page 119

Reference Manual
00809-0100-4841
Table 4-27: Pump Efficiency Alarm Parameters
Parameter
P495
P496
Pump efficiency (PE) is calculated using the rate of change (RoC) of the control unit PV
while a relay is energized. The PE value is saved in D86*; the "*" is the number of the relay
(1 to 4).
The calculation assumes that liquid continues to enter the well or tank at the rate just prior
to the relay energizing (pump starting).
The control unit continuously calculates the rate of change, sampling a new control unit
PV every 5 seconds.
Over the next 9 pump starts, a further 9 change of RoC values are stored such that the
control unit can then calculate an average value in change of RoC. This average value,
"RoC100" is then taken as being equivalent to the pump operating at 100% efficiency. A
value of 100% is then stored in D86*.
Each subsequent pump start, and change in RoC thereafter, is used in a rolling average
calculation for a new average value in change of RoC, RoCnew, which is then compared to
the previous value "RoC100" and a new PE percentage value calculated using:
PE % = (RoCnew/RoC100) × 100
If the resulting PE is greater than 100%, the RoC100 is updated to the new value and the PE
is re-stated as 100% based on this new value.
If the resulting PE is less than 100%, then the PE is calculated as above and stored in D86*.
If the PE is below the limit set (P495), the PE alarm condition is true. To indicate an alarm
by Relay or Current Output, a method must be selected.
Note
The alarm condition is automatically cleared if the calculated PE rises above the limit
(P495) by 5% or more.
Related information
Auxiliary functions for relay modes
Rate of change mode relay
Emerson.com/Rosemount
Description
Pump effy limit It is an alarm condition while the calculated pump
efficiency is below the limit defined by P495. The
pump efficiency calculation is based on the rate of
change of the control unit PV (D800) and is
independently monitored for each selected relay
(P496).
Pump efficiency values for relays are saved in D861
to D864, located in the MONITOR menu.
Pump effy RL Select relays for pump efficiency limit monitoring
operation.
Each digit represents a relay. Relay RL1 is selected by
editing the first digit to be a "1". Similarly, relay RL4
is selected with the fourth digit. (Relay RL5 does not
support this feature.) To de-select a relay, change
the appropriate digit to a "0".
Getting started
January 2021
Factory default
0% = OFF
0000
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