Flow Meters

The operation of this type is by making contact with a known amount of heat into the flow stream and measuring the relative temperature change or a probe is maintained at the constant temperature and required energy is measured. The main parts of a basic thermal flow meter consist of an electric heater in between two temperature sensors. The heater can be extended into the stream of the flow or can be placed at the pipe external.

There are two operating modes for the thermal mass flow meter. The electric power remains constant and measures the increase in temperature in one operating mode while the other mode maintains the temperature difference as a constant and calculates the electricity required to maintain it. The second method of operation gives much more range in the meter.

Another type of turbine meter is the axial turbine flow meter in which the rotor revolves around the flow axis. Axial flowmeters are used for oil measurements, industrial gas, and liquid measurements. These meters vary in terms of the design of the rotor and blade quantity. The shape of the axial flow meter for liquid measurement is completely different from the flow meter used to measure the gas.

These meters are mainly employed in industries like oil, automotive, laboratory, and water treatment. Sometimes they are installed in applications that are found in the chemical and beverage industry.

The Electromagnetic flow meter is an instrument used to determine the flow rate of the liquids in pipes according to Faraday’s Law. The flow meter consists of two parts, transmitter and sensor to measure the flow rate. The sensor of the flow meter is placed at the inlet of the pump to measure the induced voltage. The transmitter part converts the voltage value to an equivalent flow rate.

These conductive liquids passing through the magnetic field produce a voltage signal sensed by the electrodes located on the flow pipelines. The voltage signal produced is directly proportional to the flow rate of the liquid. Or we can define it as; more voltage is produced when the liquid movement is faster. The electromagnetic flowmeter determines the flow rate by processing the generated voltage signal.

The electromagnetic flow meter is a velocity flow measurement device. It measures the volume flow of conductive liquids. It not only has a site display. It can provide standard current signals like 4-20mA. For recording and adjust controls to realize automatic detection and long-distance signal transmission. It can measure the flow of many kinds of liquids. Like slurries in water, wastewater, chemical, dairy, and so on. It can also use in many kinds of industries such as food, beverages, pharmaceutical, petrochemical, steel, paper, and mining, etc. The structure of the instrument has a compact and remote type.

• There are no moving parts in the measuring tube, so it is convenient for maintenance.
• There are no flow obstructing parts, so it has a low-pressure loss.
• The lowest conductivity of the tested liquid is ≥20μs/cm, with various lining materials.
• Used to measure the flow of different acids and alkalis such as salt solutions, slurry, mineral pulp, and paper pulp, etc.
• High accuracy is guaranteed. The induction voltage of the sensor has a direct relation with the average flow rate.
• The properties of corrosiveness, viscosity, pressure, density, acidity, and alkalinity do not affect the performance of the flow meter.
• It has low-frequency rectangular wave excitation. But it doesn’t have an effect on the facility frequency and varied interferences in order that it ensures stable and reliable measurement.
• Not affected by the direction of the fluid, both positive and negative flow can be accurately measured.
• With an LCD backlit display, parameters can be modified on-site conveniently. The unit can detect if the pipe is full or drained /empty with an empty pipe detection/alarm function.

When choosing the installation location of an electromagnetic flowmeter following requirements have to be noticed to ensuring the stable and reliable performance of the sensor

• The flow meter should be placed away from the devices like motors, transformers, frequency conversion instruments as they pose large magnetic fields.
• Please better install in a dry and ventilated place, not a humid
• The environment temperature should not be more than 60 °C and relative humidity not is more than 95%.
• Choose a place where is convenient for operation and to avoid negative pressure. The flow meter shouldn’t be installed at the inlet of the pump.
• The pump valves should always be mounted on the downstream side of the flow sensor.

• The flow sensor needs to mount in a vertical position. The flow direction will always be upward when the flow sensor is mounted vertically.

The steps to be followed while choosing the line position.

• The medium should always be full-filled in the pipe from the installation location. This helps to avoid gas sticking fast to the line.
• When the sensor is not fully filled, it can raise the end pipeline of the flow meter and makes it is full
• The front and rear straight pipes are ≥10DN at the front of the flow meter and ≥5DN at the back

• The remote type signal cable should use a customized dedicated cable.
• A Yz medium-sized rubber sheathed cable is optional for the excitation cable. Its length is the same as that of the signal
• Signal cables are strictly separated from other power sources.
• The signal cable and excitation cable should be as short as possible. The excess cables should not roll. The excess cables should be cut off and the joints should be re-welded.
• When the cable is connected to the electrical interface of the sensor, insert a U-shape at the port. It prevents rainwater from penetrating into the sensor

Electric potential difference is not allowed between measuring sensors and shells. Also, converter protection grounding. A separate ground connection is preferred for the electromagnetic flowmeters. If grounding together with other instruments or electrical devices. The leakage current in-ground wire may produce series mode interference to the measurement signal. It could cause the electromagnetic flowmeter can not to work.

The electromagnetic flowmeter is used to measure the flow of liquids like water, acids, and slurries in pipes. The proper measurement is obtained when the liquid has an electrical conductivity of more than 5μS/cm. The flow measurement in low conductive liquids using the electromagnetic flowmeter is very rare. The deionized water, Hydrocarbons have low conductivity and this will turn off the flow meter.

The flow meter can be applied to clean, sanitized, contaminated, and corrosive fluids as they do not obstruct the flow. Electromagnetic flow meters are applied to conductive fluids for flow measurement.

In water treatment plants, electromagnetic flowmeters are used to measure the treated and untreated sewage, chemicals, process water, and slurries. With correct attention to materials of construction, the flow of extremely corrosive liquids (such as acid and caustic) and abrasive slurries are measured. Corrosive liquid applications are normally found within the industry processes and in chemical feed systems in most industries. Slurry applications are normally found within the mining, extraction, pulp and paper, and effluent industries.

The flow meter orientation is in a way that the device should be completely filled with liquid. There will be a drastic change in the flow measurement if the flow meter is not completely filled with the fluid.

The working of electromagnetic flowmeters in the vacuum can lead to the flow meter liners

collapse and can get sucked into the pipeline which in turn damages the flow meter. Likewise, the high temperature in the magnetic flow meter also can result in damage to the flow meter.

The electromagnetic flowmeters are mainly used in a wide range of applications for flow measurements. Electromagnetic flow meters are more suitable than other types of flow meters in the industries like paper industry, food processing industry, oil & gas industry, water treatment plants, sand water slurry, chilled water units, water, wastewater management, fluids from process industries, hot liquids, viscous fluids, etc.

• The electromagnetic flowmeters are very useful in the quantification of potable water.
• In construction sites, for the flow measurements of slurries.
• To measure the flow of combustible fuels in petroleum plants
• To measure the displacement of abrasives, explosive liquids, and paints.
• Useful in irrigation purposes

There are a lot of benefits of using an electromagnetic flow meter to determine the flow rates of the liquids. Some of the significant benefits of the electromagnetic flow meter are listed below;

• The power consumption is comparatively less
• Can detect the flow rate in liquids with dirt particles.
• The flow rate is not much affected by the factors such as temperature, pressure, viscosity, and density of the liquid.
• Can be used to determine the low flow rates as well as high flow rates

Even with the above advantages, the electromagnetic flow meter has some disadvantages also.

• Effective only for liquids that are conductive
• With respect to the size and capacity, it can be heavy.
• The usual problems with magnetic materials like hydrodynamic effects can affect the normal flow pattern. This can disturb the speed of the flow which in turn interrupts the operation.