BACKFLOW REJECTION
The DFM-IV can be forced to zero under backflow conditions by connecting external, voltage free
control relay (dry contacts) to the DFM-IV connection terminals marked INPUT.
Typically the external relay will be energized or de-energized in tandem with a pump or control valve.
The external relay must be voltage free (the DFM-IV generates a low-voltage DC current across the
INPUT terminals). In response to the external relay contact closure the DFM-IV display and outputs will
drop to zero, the Totalizer will not increment and the message
Backflow Rejection will be
displayed.
Page 17
DFM-IV Doppler Flow Meter
Manual Series A.6
A
B
INPUT
EXTERNAL RELAY
(VOLTAGE FREE
DRY CONTACTS
BY CUSTOMER)
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