Emerson FISHER FIELDVUE DLC3010 Instruction Manual page 54

DLC3010 Digital Level Controller
Configuration
May 2018
Low Alerts
D Lo Enable— On or Off. Lo Enable activates checking the primary variable against the PV Lo Threshold. The Lo Alert is
set if the primary variable falls below the PV Lo Threshold. Once the alert is set, the primary variable must rise above
the PV Lo Threshold by the PV Deadband before the alert is cleared. See figure 4‐10.
D PV Lo Threshold— Primary Variable Lo Threshold is the value of the primary variable, in engineering units, which,
when violated, sets the Primary Variable Low Alert.
D Edit Lo Threshold— Method to change the PV Lo Threshold. The entered value is checked against the other
thresholds to help avoid overlap.
D LoLo Enable— On or Off. Lo Lo Enable activates checking the primary variable against the PV Lo Lo Threshold. The Lo
Lo Alert is set if the primary variable falls below the PV Lo Lo Threshold. Once the alert is set, the primary variable
must rise above the PV Lo Lo Threshold by the PV Deadband before the alert is cleared. See figure 4‐10.
D PV LoLo Threshold— Primary Variable LoLo Threshold is the value of the primary variable, in engineering units,
which, when violated, sets the Primary Variable Low­Low Alert.
D Manage LoLo Alert — Method to coordinate Lo Lo alert configuration with alarm jumper and other alerts.
Note
If the Lo Lo Alert is enabled and tripped, the digital level controller output will go to 3.75 mA or above 22.5 mA, depending on the
position of the alarm jumper. Consider the effect of an alarm annunciation on the process, then set alarm jumper position
accordingly.
When Output Action is 'Direct':
D
A Hi alarm setting will result in an alarm-state output consistent with a very high process.
D
A Lo alarm setting will result in an alarm-state output consistent with a very low process.
When Output Action is 'Reverse', these relationships are swapped.
See figure 4‐7 and 4‐9, and examples below, to clarify the shape of the Analog Output transfer function under various PV alert
configurations. Note that the Low Alarm Current capability is not NAMUR NE 43 compliant.
Examples:
If the device is driving a valve in a series analog loop, you would normally want to use an alarm current value that will move the
valve in the direction that clears the alarm situation. A Lo-Lo alarm condition should generate a signal that will stop a vessel from
running dry or contaminating the sump.
If the control valve is in the outflow or dump line you will want to close the valve. If the dump valve opens for an increasing current
signal, you would select Plot A in figure 4‐9 (LoLo Alert enabled, Low Current alarm jumper position, Direct action).
To keep a vessel from running dry when the control valve is in the inflow pipe, you will want to open the valve. If the fill valve opens
for an increasing current signal, you would select Plot B in figure 4‐9 (LoLo Alert enabled, High Current alarm jumper position,
Reverse action).
If the device is driving the input to a control system that uses NAMUR NE 43 levels to alarm instead of directly driving a valve, you
might choose the High Current alarm jumper position even for Direct action (Plot C in figure 4‐9), as the DLC3010 low current
alarm isn't low enough to guarantee a NAMUR NE 43 trip (Plots A and D in figure 4‐9).
If the control system receiving the DLC3010 4-20 mA signal has its own PV alert thresholds and alarm strategy, you would
probably disable the DLC3010's internal LoLo PV alert and use only the control system's PV alerts. (The DLC3010 hardware alerts
would still drive the analog output signal to the Alarm Jumper setting in that case.)
In a Multi-Drop network (device has a non-zero Polling Address) alarm annunciation is disabled and the device is not directly
driving any effector, so jumper setting is not a concern.
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Instruction Manual
D102748X012