Chapter 2 - System Description - Garnet SeeLevel II 900-D4S Single Manual

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 fibre 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 1/2
inch diameter polyethylene pipe with a head at the top end where
the fibre 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. 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 900D4S Manual