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CHAPTER 2 - SYSTEM DESCRIPTION
T
he SeeLeveL II consists of a sender bar, a donut shaped float,
a fiber optic interconnect cable, and a display. The sender
bar is mounted vertically in the tank with the float sliding up and
down around it in accordance with the fluid level. The sender bar
sends the fluid level and temperature information via fiber optic
cable to the display. The temperature is the average value of the
sensors below the fluid level, so the air temperature above the
fluid is ignored. The display shows the level, volume, temperature
and alarm status to the user, and provides alarm and remote
communication outputs.
The Sender and Float: The sender bar consists of a flexible 3/4
inch aluminum reinforced polyethylene pipe or a 1 inch 316
seamless stainless steel tube with a head at the top end where the
fiber optic cable connects. It is secured at the top of the tank by
a compression fitting just below the head, and is secured at the
bottom of the tank by an anchor fitting. The compression fitting
provides the seal where the sender exits the tank, and the anchor
keeps the sender bar vertical in the tank. This mounting system
allows the sender bar to be removed from the top of the tank for
servicing without having to go into the tank.
The float is molded from polyethylene for high chemical resistance
and durability. A stainless steel float is also available. The float
contains magnets which activate reed switches inside the sender
bar to indicate the level of the fluid, which is measured with a
resolution of 1/4" throughout the tank. The activated switches
are detected by a microprocessor at the top of the bar. The use
of a digital rather than analog sensing technique lowers power
consumption to permit battery operation and ensures high accuracy
with no drift or degradation. The sender optically transmits the
level and temperature information every two seconds via an LED
located in the head, so the LED will appear to flash once every two
seconds. There are electronic temperature sensors located every
16 inches inside the bar, one sensor is sampled and a new average
is obtained every 2 seconds. For a 50 foot long bar, there are 37
sensors, which would require 74 seconds to sample all of them.
All of the sensors below the fluid level are included in the average;
the sensors above the fluid level are excluded, so the average
temperature is for the fluid only, not the air or vapor above the
fluid. The microprocessor operates from a 3.6 volt lithium battery
module giving over 5 years of life, the battery module can be field
replaced with simple hand tools.
Page 4
900D6D Manual
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