Radar level gauge
Radar level gauge is currently one of the most popular level measurement methods used in the fuel storage industry (gasoline). Radar level measurement was originally developed for use in crude oil carriers because it was necessary to measure the amount of oil using non-invasive devices. The main drawback of radar systems is “distance blocking” (use of radar level gauges).
The term refers to an example in which the surface of the tank chamber is so close to the radar device that it is no longer possible to transmit the radar signal transmitted from the liquid surface to the detector in a meaningful manner. Radar systems have no moving parts and thus have less mechanical wear compared to the device’s servo sensing technology.
But because these systems have an electronic company, the aging of the circuit components can be due to the possible failure of the system. First-generation radar level measurement systems still offer accurate measurements for up to 30 years from initial installation. The advantage of radar systems over servo sensing systems is that, as they age with work, radar systems are more cost-effective than the cost of repairs that are expected to be performed for a similar servo-sensor measurement system. Becomes. The same activity There are two types of radar level measurement systems used in the gasoline storage industry.
- Contact radar tank gauge
- Tank gauges without radar contact
Contact the tank gauge radar
As the name implies, this method requires the system to be in contact with stored fluids to measure the radar tank.
Figure: Simple diagram to show a radar level measurement system in contact
Contact with radar sensors has a probe, known as a “waveguide” in the tank, which is used to transmit measurements by transmitting a periodic pulse. The transmitted pulse reflects the level of stored gasoline, which in turn is detected by a sensor using one of the following methods:
- Domain Timer Reflection (TDR)
- This includes low-efficiency and low-power DC measurement methods
- TDR-based Guided Wave Radar (GWR)
- The phase difference sensor (PDS) detects the amount of change in the phase angle of the material in the container.
No contact with radar tank row
To measure the level of non-contact radar, no waveguide is used to transmit the radar signal to the stored liquid level. This signal transmits the radar directly to the free space of the storage tank. The signal is then reflected to detectors mounted in the tank, out of reach of stored material.
Figure: Simple diagram to show a contactless radar level measurement system
This tank gauge is often located in a fixed well. A fixed well is a more controlled environment in which surface measurements can be made. This radar propagates from fixed wells deeper into the main tank. This eliminates the possibility of misuse due to false echo caused by internal reservoir barriers.
Testing of radar level measurement systems
One way to test a radar level measurement system, suggested by a reputable manufacturer, is to place a steel plate at a specified distance from the transmitter. The signal transmitted from the metal plate is then reflected instead of the liquid surface. This is a preferred tool for system testing because it can be done on site, but does not force the operator to interact with stored materials and have related safety consequences.
It has been suggested that radar systems are especially suitable for measuring the level of products with low dielectric constant, for example, products such as LNG and LPG. Guided radar level measurement systems, if properly adjusted, can achieve a maximum measurement accuracy of 2 mm to measure process levels.
If necessary, more accuracy can be obtained for financial measurements. Integrated system manufacturers who specialize in gasoline level measurement programs show that radar systems are one of the most desirable level measurement methods currently used in the gasoline storage industry. It is better for tanks that store only one type of product (called “fixed service”). The advantage is that there are no moving parts and it is relatively inexpensive.
One disadvantage of radar systems is that they can be problematic when installed properly. Radar system problems are usually experienced during the life cycle installation phase. These can be due to the presence of steam or blockage in the tank, which causes echoes. Therefore, the design of the radar level measurement system is very important and system designers should pay attention to where the transmitters and receivers are located to minimize the impact of factors such as vibration and echoes.
Successful installation of a radar system requires filling and emptying the tank to determine the accuracy of the surface measurement. In practice, however, this is rarely practical because tanks generally contain some material, so signs of delay in surface measurement problems may occur. When tanks are too full or too close to empty, accuracy is reduced due to tank reflection.
Tank reflection is where the return signal from a surface other than the product surface is considered. Reflections can come from tank walls, instrumentation enclosures that enter the aggressive tank, or usually tank furniture / fittings such as interior stairs. Uncertainty in measurement can also be experienced if the product is present in the tank as it causes the return signal to scatter or reach the receiver further.
Although this is a significant issue, newer versions of this type of radar system compensate for the ripple effect of the product. Long narrow tanks are a problem for radar systems and therefore the amplitude / width of the radar transmission beam is very important. Nevertheless, the accuracy in the order of 1 mm with radar level measuring systems is well installed and well maintained, which is comparable to the measurement accuracy of servo systems. Integrated system makers have emphasized that the major causes of degradation in measurement accuracy over time can be attributed to the following reasons. It should be noted, however, that these named causes are not usually associated with gasoline storage.
- The signal-to-noise ratio (SNR) can increase over time due to the crystallization of the stored product. This is not an issue for gas storage but it should be certified for this type of system.
- Stored product, again gasoline is not a problem, it can damage the antenna and lead to the destruction of measurement accuracy.
This method of measuring the surface has been shown to measure up to 10 mm / m incorrectly in the presence of light hydrocarbon materials. Radar level measurements using heavy hydrocarbon materials do not experience errors of this magnitude, assuming they are designed and properly tuned for the application. As a separate note, although gasoline (fuel) storage tanks do not have such equipment, another source of inaccurate measurement with radar systems is interference with process equipment such as tank mixers .
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