Rosemount 3491, Справочное руководство, Страница: 89 / 152

Reference Manual
00809-0100-4841, Rev. AA
May 2007
4-57
Rosemount 3490 Series
Select relays for monitoring operation associated with the pump efficiency
limit. 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". This parameter is to be used with parameter P495.
Pump efficiency values for relays are saved in D861 to D864, located in the
MONITOR menu - see “Health Check: 3490 Series Control Unit“ on page 5-2.
Pump Efficiency Explanation
Pump efficiency (PE) is calculated based upon the rate of Change (RoC) of
the MCU PV whilst any single pump is on.
The pump efficiency value, (D86*, where “*” is the number of the associated
pump relay 1 - 4) is calculated only whilst that pump is operating. The
calculations will pause when the pump stops or when other pumps start.
Calculations re-start when the relevant pump starts again.
To calculate the pump efficiency, the 3490 Series Control Unit assumes that
liquid continues to enter the well or tank during pump operation at the rate just
prior to the pump starting.
The 3490 Series Control Unit continuously calculates the RoC of the PV,
making a new measurement every 5 seconds, as described in Section “Rate
of Change Relay“ on page 4-53. Once the selected pump starts, the 3490
Series Control Unit will monitor and record the change in RoC over the next 5
measurements. Over the next 9 pump starts, a further 9 change of RoC
values are stored such that the 3490 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 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 percentage is greater than 100%, then the RoC100 is updated
to the new value and the PE re-stated as 100% based on this new value.
If the resulting percentage 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 - refer
to “About Alarms“ on page 4-60.
NOTE:
The alarm condition is automatically cleared if the calculated PE rises above
the limit (P495) by 5% or more.