KROHNE BM 90 EN - Manual (Page 31)

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4.5. Open channel Flowmeter (Pr.1 = 4)
The application : l Rectangular flume, with a max. flow of 150 l/s at head 0.3 m
l Loss-of-echo indication to telemetry system
l 4-20 mA signal proportional to flow
l Totalise flow and provide pulsed output to external totalizer
l Display flow reading
Pr. 1 = 4 To define open channel flow metering.
Pr. 2 = 4 As distances are small, work in cms.
Pr. 3 = 120 Distance of trans. from bottom of channel.
Pr. 4 = 30 Level at which max. flow rate value is defined.
Pr. 5 = 50 Blanking zone into which level will not rise.
It is suggested that this is above the top of the channel to allow
the system to continue reading up to that level.
Pr. 6 = 50 Rate of Change of level 50 cm/min.
Pr.17 = 7 Relay 4 assigned to indicate loss-of-echo to the telemetry unit.
Pr.20 = 5 Relay 5 to operate as external totaliser switch.
Pr.28 = 3 Analogue output "holds" on failsafe, as factory set.
Pr.29 = 120 Failsafe time is left at default of 120 s.
Pr.30 = 1 4-20 mA output fixed to span (Pr.4).
Pr.31 = 2 Analogue output represents flow rate.
Pr.37 = 2 Probe enable if Temperature Compensation is used
Pr.45 = 2 To define that a rectangular flume is being used.
Pr.46 = 39 Defines the max. flow is 39 l.
Pr.47 = 1 Flow in Pr.46 is in litres per second.
Pr.48 3 To avoid totalizer overflow, totalise in cubic meters rather than litres.
Pr.49 = 1 Sets external totaliser to same as internal totaliser.
Pr.78 = Simulate the program.
Pr.98 Clear and initiate the totalizers.
Note : In normal ’RUN’ mode display will always show Flow. Instantaneous readings of
"High total", "Low total", "Head" and "Flow" can be obtained by pressing keys 1 to 4. The
display will revert back to Flow after 15 seconds.
120cm
(Pr.3)
120cm
(Pr.3)
Transducer position
3-4 times max. head.
30cm
(Pr.4)
Flow
90-120cm
50cm
(Pr.5)