KROHNE BM 90 EN - Manual (Page 30)

30
4.4. Differential level mode (Pr.1 = 3)
In the differential mode, the transceiver drives two transducers, to measure the difference in levels by subtracting the
downstream level from the upstream level.
Please refer to connection diagram Fig. 6 for transducer wiring.
The upstream transducer should be chosen to give a positive differential value.
The application :
l Start rake when differential reaches 0.15 m
l Stop rake when differential falls to 0.05 m
l Maximum differential 0.3 m
l Alarm if level on upstream side exceeds 0.6 m
l Loss-of-Echo indication to telemetry system
l 4-20 mA signal proportional to differential
Pr. 1 = 3 To define differential level measurement.
Pr. 2 = 4 As distances are small programme in cms.
Pr. 3 = 120 The distance from bottom of channel to transducers in cms.
Pr. 4 = 30 The maximum differential span in cms.
Pr. 5 = 50 Blanking zone in cms.
Pr. 6 = 100 The max. rate of change of level in cms.
Pr. 8 = 3 Relay 1 designated for differential control.
Pr. 9 = 15 Relay 1 energises at diff. 15 cm to start rake.
Pr.10 = 5 Relay 1 de-energises at diff. 5 cm to stop rake.
Pr.11 = 5 Relay 2 to alarm on an upstream level.
Pr.12 = 60 Relay 2 de-energises at 60 cm high alarm.
Pr.13 = 55 Relay 2 energises at 55cm to clear high alarm.
Pr.17 = 7 Relay 4 assigned to indicate loss-of-echo to the telemetry system.
Pr.23 = 2 Switch rake off on failsafe.
Pr.24 = 3 Hold alarm level indication on failsafe.
Pr.28 = 3 Analogue output holds on failsafe.
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.97 = 2 This counts the number of times the rake is turned on, and how
(optional) many hours it has been energised.
120cm
(Pr.3)
30cm
(Pr.4)
RAKE CONTROL
50cm (Pr.5)
15cm (Pr.9)
Start rake
Stop rake
5cm (Pr.10)
Flow
60cm
(Pr.12) 55cm
(Pr.13)