Tank Gauging Management SystemsMarine/Products
Substantial improvements on magnetostrictive liquid level sensors have recently been achieved, making them more attractive for use in Automatic Tank Gauging (ATG) systems.
The improvements include flexible probes that are much easier to install and bottom-referenced probes which allow for more accurate readings for a storage tank. Such liquid level sensors are the key element in magnetostrictive tank gauges, which offer certain advantages over other types of automatic tank gauges.
COMMON TYPES OF ATGs
- Radar Gauges
- Magnetostrictive Gauges
- Hydrostatic Gauges
- Servo-Powered Gauges
- Float & Tape Operated Gauges
TECHNOLOGY BREAKDOWN
Radar Gauges: Popular for their accuracy. They are particularly useful in gauging tars and other products not suitable for contact-type sensors.
Magnetostrictive Tank Gauge (MTG): Provides superior accuracy for liquids that can accommodate a float. It is not affected by motion of the tank top. In addition, it can incorporate averaging temperature measurement into its liquid level probe.
Hydrostatic Tank Gauges: Provide direct reading of mass but are less accurate for level.
Servo-Powered Gauges: Can provide good accuracy but have a higher installed cost.
Float Operated Gauges: Widely used in the past but are losing popularity due to maintenance demands.
Typical Applications :
Overview
MOWE Tank Gauging Systems :
Other Systems :
Configuration
Feature :
Solution
A complete solution to our customers comprises of key components ranging from Field Instruments, data acquisition systems, processors and human machine interface (HMI) devices.
Our team of engineers, with over 20 years of experience in the Marine and Offshore industries, not only builds systems but also designs reliable and proven solutions tailored to customer requirements.
RADAR SYSTEMS
MOWE works closely with recognized radar equipment manufacturers to provide complete Marine Radar Tank Gauging solutions, delivering proven and reliable systems to our customers.
Pulse Radar Technology
Pulse radar is a radar sensor in K-band technology (emitting frequency approx. 26 GHz) for continuous level measurement.
Available Antenna Configurations:
The antenna of the radar sensor emits short radar pulses with duration of approx. 1 ns. These pulses are reflected by the product and received by the antenna as echoes. The running time of the radar pulses from emission to reception is proportional to the distance and hence to the level. The determined level is converted into an appropriate output signal and outputted as measured value.
Power Supply: Via Profibus DP/PA segment coupler or LOG 571 EP cards.
Data Signal: A two-wire cable acc. to Profibus specification serves as carrier of both power and digital data signals for multiple sensors.
Standpipe Requirement: Under these requirements, the measurement of products with low dielectric values (from DK value 1.6) is possible. Surge or bypass tubes must extend all the way down to the requested min. level.
FMCW Radar (Frequency Modulated Continuous Wave)
Range of Applications
FMCW Level-Radar level gauging system is designed to measure the distance, level, volume and reflection of liquids, pastes, slurries, solids and particulate materials.
Operating Principle
A radar signal is given via an antenna, reflected on the measuring surface and received after a delay time t. For further signal processing the difference ∆f is calculated from the actual transmit frequency and the receive frequency.
The difference is directly proportional to the distance i.e. a large frequency difference corresponds to a large distance and vice versa. The frequency difference is transformed via a Fourier transformation (FFT) into a frequency spectrum and then the distance is calculated from the spectrum. The level results from the difference between tank height and distance.
Linearity of Frequency Sweeps
The measuring accuracy of an FMCW radar is determined from the linearity of the frequency sweeps and their reproducibility. The linearity correction is deduced via reference measurement of the oscillator. An immediate frequency regulation is necessary with the device because of the higher demand on the measuring accuracy.
With the PLL technology (Phase Locked Loop) the signal frequency is directly recorded as a digital data and the converter oscillator locks automatically on the right frequency.
GUIDED - RADAR SYSTEMS
Measuring Principle
High frequency microwave pulses are coupled on a cable or rod and guided along the probe. The pulses are reflected by the product surface and received by the processing electronics. A microcomputer identifies these level echoes which are measured, evaluated and converted into level information by the ECH software.
Thanks to this measuring principle, the adjustment with the medium is no longer necessary. The instruments are preset to the ordered probe length. The cable and rod versions (shortable) can be adapted locally to the individual conditions.
Performance Benefits:
Applications:
HYDROSTATIC PRESSURE TRANSMITTER
In the case where the fluid is at rest, called fluid statics or hydrostatics (from hydro meaning "water" and static meaning "at rest"), the force acting on the object is the sheer weight of the fluid above, up to the water's surface—such as from a water tower. The resulting hydrostatic pressure (static pressure) is isotropic: the pressure acts in all directions equally, according to Pascal's law.
Our pressure transmitters work acc. to the hydrostatic measuring principle, which functions independently of the dielectric properties of the product and is not influenced by foam generation. The sensor element of is the dry ceramic-capacitive CERTEC® measuring cell, Stainless Steel, Titanium etc. Base element and diaphragm consist of high purity sapphire-ceramic. The hydrostatic pressure of the product causes via the diaphragm a Capacitance change in the measuring cell. This capacitance change is converted into an appropriate output signal On board vessel, it is well suited for Ballast tanks whereby submersion in seawater do not affect the long term accuracy of the transmitter.
Protection On-Board & Dock Equipment
Monitoring the pipeline pressures at the manifold ensures the safety of on-board and dock equipment, and provides the basis for pump control.
If pump output is too high or if valves remain closed during charging and discharging processes, gauge or low pressure in the product pipelines can result. This can cause severe structural damage to the manifold or the storage tanks.
On-site pressure indication provides additional security for processes involving the manifold. Choosing an appropriate pressure instrument becomes therefore crucial for this particular application whereby location indication is just as important as remote readout.
Draught, Trim and List
The most important measurements on board are the measuring points for calculating draught, trim and list. Ship safety depends heavily on them.
Using the transmitted values from the different measuring points, the load master, as part of the cargo control system (CCS), can determine the exact values of ship orientation and draught.
Standard Measuring Allocation
Required Specification: Instruments with an appropriate IP68 protection rating must be utilized to withstand continuous submersion and harsh marine environment levels.
Service and Settling Tank
To ensure fuel feed to the main engine, the separated heavy fuel oil (HFO) is first pumped into the settling tank (buffer tank). The connected service tank (day tank) is filled via continuous overflow from the settling tank and is connected directly with the main engine.
Thermal Conditions
Heating coils in both tanks ensure an even temperature between +75°C and +90°C (+167°F and +194°F) which keeps the heavy fuel oil pumpable and flowing correctly.
Choosing the correct apparatus that can withstand the high temperature and sludge environment is therefore very important for the long-term life of the apparatus.
MOWE Recommendation: We highly recommend an instrumentation setup which has minimum contact to the extreme heat and heavy oil, such as a specialized Guided Radar Instrument.
Monitoring the Bilge
Every motorised ship has a so-called bilge well, i.e. a space between the floor of the engine room and the bottom of the ship. A water/oil mixture collects in this space at the lowest point of the vessel.
The collected mixture is then processed and separated into clean water and oil components by an on-board skimmer and demulsifying unit. After passing through various cleaning processes, the pure water can be safely pumped out.
Control System Engineering: The bilge de-oiling equipment loop is fundamentally automated and controlled by safety level switches.
MOWE Engineering Standard: Mowe recommends a highly reliable level switch system for this heavy application to minimize the frequency of changing or maintaining this instrument over extended operational periods.
Fresh Water and Grey/Black Water
Fresh water is an essential commodity on a ship and is stored strictly within separate, dedicated holding tanks.
Depending on the specific class, type, and size of the ship, different volumes of fresh water are demanded for drinking consumption, personal hygiene, and general cleaning maintenance. The typical volume capacity stored in the tanks can scale from 50 to 400 tons, depending heavily on whether the vessel operates an integrated desalination plant.
Grey & Black Water Measurement
Waste water is treated on large ships in on-board clarification plants, or stored in specialized grey/black water holding tanks to await final shore disposal.
Due to the large concentration of solid particles and the constantly shifting density of the internal tank fluids, non-contact level measurement engineered with Ultrasonic Technology qualifies perfectly for this severe application.
Fresh Water Measurement
Direct electrical measuring principles are mandatory for safe potable level management.
MOWE Recommendation: MOWE recommends robust flange side-mounted instruments. Flanged directly onto the tank shell, liquid level is measured reliably and accurately.
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