What is the purpose of the Signal Strength Display and Sensitivity adjustment?
Doppler signals of low strength (left of the
X
on the
SS
signal strength display) are not accepted or
processed by the instrument. This feature assists in rejection of environmental noise and vibration. For
optimum noise rejection the sensitivity control should be adjusted so that signal strength is to the right of
the
X
on the signal strength display with flow and to the left of the
X
with no flow.
Can I change the length of the sensor cable?
Yes. Technological advances in Greyline Doppler design allow cable lengths up to 500 ft (152 m) with
no loss of signal strength. Extended cable (Greyline Option XC) should be installed in rigid or flexible
conduit for mechanical protection. Use only Greyline shielded coaxial pair (RG174U) cable. Cable
junctions should be made through a terminal block and housed in a watertight metal junction box
(Greyline Option JB). BNC coaxial connectors (TV cable type) are not recommended for cable splices.
Does the DFM-IV require periodic recalibration?
No. DFM-IV calibration does not drift over time. The solid state sensor has no moving parts to wear and
affect calibration. The Doppler flow technique generates an ultrasonic signal proportional to the velocity
of flow. All Greyline timing/counting circuits use crystal-controlled frequency references to eliminate
any drift in the processing circuitry.
Page 23
DFM-IV Doppler Flow Meter
Manual Series A.6
