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2150EX Area Velocity Flow Module
Section 2 Preparation and Installation
2-30
CAUTION
Make sure the slots on the AV sensor carrier are completely
pressed into the tabs on the ring. This is particularly important
where there is any possibility of reverse flows, or where flows
are of high velocity. If the AV sensor is not fully pressed into the
mounting ring tabs, it might come loose in the stream, and
could possibly be damaged or lost.
Make sure the sensor cable is securely fastened along the
back (downstream) edge of the ring. Otherwise, the sensor
may provide inaccurate level readings under conditions of
high velocity.
To complete the sensor-spring ring assembly procedure, attach
the sensor cable to the downstream edge of the ring. Follow the
cable routing shown in Figure 2-21. Other routing directions may
affect measurement accuracy. The cable can actually create a
stilling well downstream from the sensor, causing the level to
read low. Use the self-locking plastic ties supplied with the ring.
Install the ring in the pipe by compressing it. Press inward on
both sides and slide the ring into the pipe.
Route the sensor cable out of the stream and secure it in position
by placing the ties through the holes in the mounting ring and
then locking them around the cable, as shown in figure 2-21.
CAUTION
Do not overtighten the plastic cable ties; they should be tight-
ened just enough to secure the cable in place, without greatly
indenting the cable. Overtightening the plastic ties may col-
lapse the reference tube in the cable, blocking it.
The spring ring may need anchoring. Under conditions of high
velocity (greater than 1.5 meters per second or 5 feet per second),
the ring may not have sufficient outward spring force to
maintain a tight fit inside the pipe. The ring may start to lift off
the bottom of the pipe, or may even be carried downstream.
This problem is more prevalent in the larger diameter pipes and
in pipes with smooth inside surfaces, such as plastic pipes. If any
of these conditions are present, or if movement of the mounting
ring is detected or suspected, you must anchor the ring in place.
You can do this by setting screws through the ring into the pipe,
or by other appropriate means. If there is a problem with the
smaller diameter rings, it may be sufficient to simply increase
the outward spring force of the ring by bending it into a less
round configuration.
2.8.2 Scissors Mounting
Ring
For pipes larger than 15" in diameter, Teledyne Isco offers the
adjustable Scissors Ring (also known as the Universal Mounting
Ring). This device consists of two or more metal strips that lock
together with tabs to form a single assembly. There is a base
section where the sensors are mounted, two or more extension
sections (usually), and a scissors section at the top that expands