Dynasonics DDFXD Doppler Ultrasonic Flow Meter - Manual (Page 17)

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4) Spread an even layer of coupling compound, approximately 1⁄8” (3 mm) thick, to the flat face of the
two transducers.
5) Place each transducer under the strap with the flat face – amber plastic window – positioned
towards the pipe. The notch on the back of the transducer will provide a mounting surface for the
strap. The transducer cables must be facing in the same direction and downstream of the trans-
ducers for proper operation.
NOTE: Large pipes may require two people for this procedure.
6) Tighten the strap strong enough to hold the transducers in place, but not so tight that all of the
couplant squeezes out of the gap between the transducer face and pipe. Ensure that the trans-
ducers are squarely aligned on the pipe and 180° apart. If RTV is utilized, avoid moving the trans-
ducers during the curing time – typically 24 hours – as bubbles may form between the transducer
and pipe that can reduce ultrasonic signal transmission to unsatisfactory levels.
7) Route the transducer cables back to the area where the transmitter will be mounted, avoiding
high voltage cable trays and conduits. While transducer cable extension is not generally recom-
mended, if additional transducer cable length is required, utilize cable and connectors of the
correct type and impedance. In many cases, especially if a splice my be exposed to water or other
liquids, it may be more effective to replace the entire cable. Transducers use RG59, 75 ohm coaxial
cable or Twinax (Belden #9463) or (Belden # 9463DB) 78 Ohm two conductor cable.
8) If the transducers are to be permanently mounted using Dow 732, the RTV must be completely
cured before proceeding to Instrument Start-up. Ensure that no relative motion between the
transducer and pipe occurs during the 24 hour curing process. If Dow 111 grease was used for
temporary operation of the DFX system, proceed with the Instrument Start-up procedures.
DP7 PROBE TRANSDUCER MOUNTING
The DP7 insertion transducer that is utilized by the DFX contains piezoelectric crystals for transmitting
and receiving ultrasonic sound energy. The black Ultem® plastic tip of the DP7 contains these crystals,
which are designed to be inserted just into the path of the flowing liquid.
Select a transducer mounting location that will be completely filled with liquid when flow measurements
are to be made (See Figure 2.1) and with adequate straight runs (without disturbances) of pipe, both
upstream and downstream, to achieve stable and accurate readings. Examples of minimum upstream
and downstream requirements are included in Figure 2.2. Note that if adequate straight piping cannot
be provided, the DFX system will operate repeatably, but will probably not achieve ideal accuracy.
When installing the DP7 transducer in a horizontal pipe, the preferred orientation is at least 20 degrees
from the top or bottom of the pipe – See Figure 2.4. Ensure that the mounting location allows for ad-
equate clearance to install and retract the probe fully from the pipe.
The following instructions also cover hot tapping, installations where it is required to install or remove
the transducer probe without shutting down the process pressure. If the product is being installed with-
out an isolation valve, ignore the steps that pertain to its installation. Figure 2.5 illustrates an exploded
view of an isolation valve assembly and names the various components.