Download - Model 6290 Operation
Model 6290 LTD
Third generation design guarantees quality and reliability
Probe under operator control allows monitoring of conditions at any level in the tank
Density & temperature profiles allow detection of stratification
Modbus interface allows integration with DCS
Bottom reference provides greatest accuracy
Drive Mechanism Drive Mechanism HousingHousing
Probe EnclosureProbe Enclosure
Pinch Pinch ValveValve
Ball Ball ValveValve
Flameproof Flameproof Control Unit Control Unit EnclosureEnclosure
Model 6290 LTD System
Tank FloorTank Floor
Multi-Sensor Probe AssemblyMulti-Sensor Probe Assembly
Hollow Helical Drive CableHollow Helical Drive Cable
Top of TankTop of Tank
Probe tracks liquid level
Probe drives back to liquid level (stepping motor accurately measures distance)
Level Measurement
Probe drives to bottom
Bottom reference switch activates
Liquid Level Sensors
Probe drives up
Probe drives down
Probe stops
Program logic drives probe until lower sensor touches liquid (hysteresis errors are removed)
Temperature and Density Sensor
Frequency of vibration is converted to density through an
equation in the controller
Connector
PT 100 Temperature SensorPT 100 Temperature Sensor
Pick-Up Pick-Up CoilCoil
Driving Driving CoilCoil
Vibrating SpoolVibrating Spool
To ControllerTo Controller
Tank Profile Scan
Probe tracks liquid level
Probe drives to bottom
Bottom reference switch activates
Probe drives up and stops at programmed intervals to collect profile information
Modes of Operation
Profile – Probe drives to bottom and then back up, stopping at programmed intervals to record data
Cal (Calibrate) – Probe drives to bottom of tank to establish bottom reference, then returns to liquid level and switches to Auto
Auto – Probe tracks liquid level
Top Scan – Probe starts at current position and moves up or down, stopping at programmed intervals to record data
Manual – Probe can be driven up or down according to operator commands. Reports current temperature and density, does not track liquid level.
Two Liquid Level Sensors
Intrinsically Safe “Bottom Reference” Switch
Oscillating-Spool Densitometer for use in various media:
LNG
Propane
Butane
Ethane
Calibrated Platinum Temperature Sensor
Hollow Helical Drive Cable w/
Conductors
Bottom Reference Switch Assembly
Sliding Lower Shroud
Level Sensors
270 mmto bottom of
of lower sensor
Oscillating Spool Densitometer
2 ¼” DIA (57.15 mm)
Probe Assembly Components
Temperature Sensor(Inside Densitometer)
Sliding Shroud (activates reference switch)
Drive Mechanism Housing
Pinch Valve to ball valve transition piece (Optional)
Pinch Valve with Buna liner
Probe enclosure with viewing window
Probe may be driven into Probe enclosure and sealed off from tank using pinch valve for any required maintenance.
Ball valve allows for possible removal of LTD system and assures tank integrity.
Drive Mechanism Housing
Probe Enclosure
Pinch Valve
Ball Valve
FlameproofControl Unit
Enclosure
M6290 Tank Top Items
Flameproof Control Unit Enclosure
Mechanical Unit Components
Take up reel with helical drive cable
Constant tension spring motor
Flexible coupling
Gear box/speed reducer
Drive gear
Back up wheel
Arc plate
Reel feedback switch
Spring MotorFlex coupling
Take up reelGear box
Drive gear
Arc plate
BackupReel FB sw
All electronics to control the system are contained in the control unit, housed in a flame-proof enclosure.
The control unit may not be opened in the presence of gas.
Input power is 110VAC or 230VAC.
Output of all data to control room is via 2-wire RS485.
Field wiring includes power indication and power control
Inside the Control Unit…
Control Unit Contents
Power Supplies
Power Conversion Card
Control Module
Zener Barriers
Motor Driver
Stepping Motor
Drive Coupling
Power Conversion Card
Control Module
Zener Barriers
Stepping Motor
Drive coupling
Tank Gauge Interface Module (TGIM)
Miniature Size, 1/8 DIN Configuration
Termination point for field wiring
Termination point for wiring to DCS
Possible modem connection for remote diagnostics by SI Engineers
Access point for Hand Held PC (HHPC)
Access for HHPC
Field Wiring DCS Connection
Multiple Field Bus System Architecture
LTD Gauge Data
Alarm Gauge Data
Primary Gauge Data
Secondary Gauge Data
Home Page
LTD Gauge Data
Last LTD Profile Data
LTD Alarm Status
LTD Sensor Status
LTD Gauge Detail
List of Profiles Per Day
Temperature Profile
Axes Automatically
Scaled
Density Profile
LTD Profile Display
Hazard of Rollover
Safety Hazard• Uncontrolled pressure rise in storage tank• Uncontrolled release of LNG vapor• Over-pressurization of LNG storage tank• Ignition of vapor cloud
Potential Danger• Receiving Terminals (1)• Peak Shaving Terminals (2)• Production Facilities (3)
LOWER LAYER
UPPER LAYER
VAPOR
FILM
Boiloff
Relief Valve
• Light layer on top of heavy layer
• Influx of heat increases energy
• Energy in lower layer trapped by hydrostatic pressure
• Layers converge with time
• Energy in lower layer suddenly releases
• Layers “roll over,” releasing large amounts of vapor
HEAT
HEATHEAT
HEATHEAT
Cause of Rollover
Hazard of Rollover
Rollover Incidents
• Accurate statistics difficult to obtain
• 7 Major reported incidents (1970-1979)
• 41 Unofficially reported incidents (1970-1982)
• Many (possibly 100’s) of unreported incidents
Prevention of Rollover
• Prevention of layers through proper tank filling
• Destruction of layers through mixing
• Detection of layers through instrumentation
• Continuous monitoring of tank conditions