Coriolis mass flow meters
Coriolis mass flow meter is a device that measuring the flow and density of a substance flowing through a U-shaped tube.
- Mass flow meter design
- Coriolis flowmeter principle of work
- What does a Coriolis meter measure?
- Advantages and disadvantages of Coriolis flow meters
The design of mass flow sensors can vary, but in general it consists of several basic elements:
- tube (tubes);
- pushing mechanism;
Tube. All measurements are made here. It always has a U-shape. Sometimes it can be used two such tubes.
Sensors. Special sensors are placed at the input and output of the tube. They record changes in oscillations at the system entrance and exit.
Pushing mechanism. Such device makes a tube fluctuate. It can be represented by different elements depending of the model (for example magnets), but all of them has the same purpose - to make the tube fluctuating.
Transducer. After measuring the flow and density by sensor, they need to be converted into a normal signal, for example, a digital one. After that, such information in the numerical form will be shown on display.
It is also always possible to install additional counters to accumulate and structure results autonomously.
The operation of such flow sensors is based on the Coriolis Effect. In nutshell, the Coriolis force is one of the forces of inertia that affects tube oscillations.
This method allows working with a wide variety of substances. A mass flow meter can be used to measure flow in:
- viscous materials.
When work is getting started a small device begins to push the tube which located inside the flow meter (in zone with a bend). Hence, it begins to fluctuate with a certain frequency. Sensors are installed on the two sides and record current vibration parameters.
When the tube is not filled, both ends oscillate in the same phase. On the graph of frequency oscillations, the sinusoid at the input will be equal to the parameters at the output.
Fluctuations are the main marker of work. When a substance, such as a liquid, begins to move through the pipes, the tube experiences additional distortions in frequency due to the inertia of the flow. It happens because such flow interacts with tube walls.
Due to the appearance of additional effects on the walls, the front and back sides of the tube starts to oscillate in different phases. Now their sinusoidal oscillations will have a difference in the form of a small shift between them.
Such a difference is called a shift phase and is often referred to as ∆t. The consumption directly depends on this indicator.
After the sensors have recorded changes in oscillations at both sides of the tube, the system proceeds to analyze acquired information.
With help of such a flow meter, the user can measure several parameters at once including:
- Mass flow.
Sometimes sensors can also measure temperature.
Mass flow rate is determined by comparing and analyzing the time delay between two sinusoidal phases. This phase shift ∆t is measured in microseconds (µs).
This parameter is directly proportional to the mass flow rate. The higher ∆t, the higher flow rate.
Density is also measured by analyzing sine waves in oscillations. When the flux density changes, the tube walls oscillation frequency changes too.
Consider this situation on the example of two different loads, suspended on the same springs. A bigger mass will have a lower oscillation frequency. In the same time, a spring with a smaller load will move more often.
In the case of flow meters, the same volume of different substances will have a different mass due to its density and will act as such load. The tube here is similar to a spring from example. That is, the greater the density of a substance in a stream, the lower wall frequency of oscillations.
According to this principle, the device determines the density of the measured material.
After considering the flow sensor design and its principle of work, let`s look at main advantages and disadvantages of such device.
Advantages of a Coriolis flow meter:
- Accuracy of measurements.
- High repeatability.
- No dependence on flow direction.
- Lack of moving parts.
- The minimum required tech. service.
- Ability to work with very viscous substances.
Disadvantages of Coriolis flow meter:
- A small range of dynamics.
- Large size.
- External vibration can affect the result.
- Sensitivity to temperature changes.
Some of such issues can be corrected by further improving devices design. For example, a user can minimize vibration affecting on the device by installing the equipment on rubber sealing, etc.
In general, transducers of the presented type are a simple and effective way to measure flow parameters in pipelines. However, they need stable physical conditions for operation.