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The probe transducer units, particularly when they are used as flow monitors, will give the
most accurate results with a straight run of pipe upstream and down stream of the probe.
Straight run length of 20 diameters upstream and 10 diameters downstream is recommended.
2.
TU or TUL (nonintrusive) — TU or TUL transducers particularly require special care in
handling and installing to avoid damage to sensor tube stubs.
.
CAUTION:
TU and TUL transducers are made with thin-walled tubing — use care when
installing.
All TU and TUL transducers should have straight line input and output sections, typically 20
pipe diameters on the inlet and 6 to 10 diameters on the outlet. If installed vertically, the flow
should be going up through the sensor. Connection in the line is via compression fittings, hose
with clamp, threaded fittings or flanges, whichever is appropriate. Care must be taken not to
transmit a twisting force through the transducer's midsection. The TU or TUL transducer,
whether flanged or not, must not be used to pull other piping together or to make up angular
mismatch of fittings. The integral electronics box should never be rotated for any reason.
Flow stream conditioning must also be considered to maximize meter performance. Avoid
upstream protrusions and short distance straight runs. Flow pulsations, such as those created
by metering pumps, may cause the instrument to differ from the factory calibration.
Furthermore, if the flow is varied by stroke and by pump speed adjustment, the indication will
most likely be non-repeatable. If you are using a pump of this type, it is recommended that
a pulsation dampening device be used to provide smooth continuous flow. A second choice
would require readjustment of the instrument calibration (cal) potentiometer after installation
(See
SECTION 4.2
).
For liquid measurement systems using high pressure gas to force flow, the effects of the
absorbed gas must be considered. In these cases, sudden pressure drops upstream of the sensor
such as line size expansions, control valves, and pressure dropping regulators must be avoided.
Sudden pressure drops can cause the absorbed gas to release into the liquid, making the flow
sporadic and difficult to measure. Control valves should be placed down stream of the sensor.
Fluid temperatures other than ambient require special attention. Thermal gradients from one
end of the transducer to the other (for TU and TUL transducers), as well as along the radius
of the connection pipe, are undesirable. Therefore, effective insulation should be installed
around the inlet and outlet straight line runs. Gradients which may exist in the line further up
stream can be removed if an insulated elbow is installed in the line prior to entering the
straight line portion of the plumbing. Metallic support braces for the sensor or adjoining
plumbing can act as a heat sink and cause operational problems in high temperature
applications. The support braces should be thermally isolated from the line to avoid large heat
conduction effects.
If the transducer is for use above 75
/
C, it will have an extension arm between the transducer
and the electronics module enclosure. Free air should be allowed to flow around the extension
arm and electronics enclosure to keep the electronics cool. The extension arm can be insulated
up to one-third of its length from the transducer body. Proper thermal control is vital to
accurate meter performance. Non-uniform heat tracing, relay on/off temperature controllers
and oscillating proportional type control should always be avoided. Steam traced lines with
good pressure regulation or properly tuned proportional temperature control systems are
