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DFM 5.1 Doppler Flow Meter
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 DXC) 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 DJB). BNC coaxial connectors (TV cable type) are not recommended for cable splices.
Does the DFM 5.1 require periodic recalibration?
DFM 5.1 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.
ISO 9000 or similar quality management systems may require periodic and verifiable recalibration of
flow meters. DFM 5.1 Doppler Flow Meters may be returned to Greyline for factory calibration and
issue of a new NIST traceable certificate. Refer to the ‘Product Return Procedure’ section of this manual
for return instructions.
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