Dynasonics DXN Portable Ultrasonic Measurement System - Manual (Page 26)

4. The two marks on the pipe are now properly aligned and measured.
If access to the bottom of the pipe prohibits the wrapping of the paper around the circumference, cut a piece of
paper 1/2 the circumference of the pipe and lay it over the top of the pipe. The length of 1/2 the circumference
can be found by multiplying the pipe O.D. by 1.57. The transducer spacing is the same as found in the Transducer
Positioning section. Mark opposite corners of the paper on the pipe. Apply transducers to these two marks.
1/2 Circumference = Pipe O.D. x 1.57
5. For DTTN, DTTH and DTTL transducers, place a single bead of couplant, approximately 1/2" inch (12 mm) thick, on
the flat face of the transducer. See Figure 26 . Generally, a silicone-based grease is used as an acoustic couplant, but
any good quality grease-like substance that is rated to not flow at the temperature that the pipe may operate at will
be acceptable.
6. Place the upstream transducer in position and secure with a stainless steel strap or other fastening device. Place
straps in the arched groove on the end of the transducer. A screw is provided to help hold the transducer onto the
strap. Verify that the transducer is true to the pipe, adjust as necessary. Tighten transducer strap securely. Larger pipes
may require more than one strap to reach the circumference of the pipe.
7. Place the downstream transducer on the pipe at the calculated transducer spacing. Using firm hand pressure, slowly
move the transducer both towards and away from the upstream transducer while observing signal quality. Clamp the
transducer at the position where the highest signal quality is observed. Signal quality between 5 ... 98% is acceptable.
The factory default signal quality setting is 10%, however there are many application specific conditions that may
prevent the signal quality from attaining this level.
A minimum signal quality of 10% is acceptable as long as this signal level is maintained under all flow conditions.
On certain pipes, a slight twist to the transducer may cause signal quality to rise to acceptable levels.
8. Certain pipe and liquid characteristics may cause signal quality to rise to greater than 98%. The problem with
operating a DXN with very high signal quality is that the signals may saturate the input amplifiers and cause erratic
readings. Strategies for lowering signal quality would be changing the transducer mounting method to the next
longest transmission path. For example, if there is excessive signal quality levels and the transducers are mounted in
a Z-Mount, try changing to V-Mount or W-Mount. Finally you can also move one transducer slightly off line with the
other transducer to lower signal quality.
9. Secure the transducer with a stainless steel strap or other fastener.
TOP VIEW
OF PIPE
Figure 30: Z-Mount Transducer Placement
DXN Portable Ultrasonic Measurement System
Page 26 February 2013