Hunter Industries FLOW-SYNC HFS Owners Manual Page: 21

Hunter controllers equipped with flow terminals
will haave approximately 20 VDC present on the
flow sensor terminals, with no flow input.
When flow begins, the voltage will pulse. On a
standard voltmeter, the voltage will appear to
drop, or pulsate. On voltmeters equipped with a
frequency counter, the pulse frequency can be
measured in Hz.