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Example 3 - Dual Point Differential
This mode of operation is commonly used for water and waste water processing to
monitor the level on either side of a screen or filter to identify a "blocked" screen
condition. Similar operation is also commonly used to operate waterway control gates to
maintain rivers and lakes at predetermined levels.
For this example we'll assume the following:
the river level is typically 280 m ±0.5 m above sea level.
•
•
when the river level is 280 m, the river side of the infeed channel is 125 cm.
•
a control room alarm is required if the river levels exceeds 281 meters or falls below
279 m.
•
the plant infeed channel includes a series of screens to prevent large solids from
entering.
•
under normal conditions the difference between river and plant sides of the screens
is 6 cm.
•
a control room alarm is required if the river/plant side differential level reaches 12
cm.
•
the river level rate of change is very slow (several days for a 6 cm change).
•
the plant side level decreases slow but increases fast (after screen cleaning).
•
a mA output proportional to the river side level is desired (4 mA = low, 20 mA = high).
•
a mA output proportional to the difference (4 mA = 0 cm, 20 mA = 12 cm) is also
required.
•
Transducer 1 (an XPS-10) is mounted on the river side of the filter, 275 cm above the
channel.
•
Transducer 2 (an XPS-10) is mounted on the plant side of the filter, 275 cm above the
channel.
225cm
(P101)
25cm
(P102)
Page 102
transducer 1
river side
12 cm
(P112)
AiRanger DPL Plus – INSTRUCTION MANUAL
transducer 2
plant side
242.0cm
7ML19981BD02
275.0cm
(P006)
(P007)
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