Various Types of Flow Rate Measuring Instruments

Flow rate measuring instrument is one instrument that measures the flow rate or amount of fluid per unit time. Flow rates can be expressed in several units such as gallons per minute (GPM), liters per second, cubic feet per second (CFS), etc. The most common types of flow rate measuring instruments are described as follows: Read below on the Measure flow rate and its type as explained here.

Flow Rate Measuring Instruments

1. Turbine Flow Meter

 A turbine flow meter is an instrument with a rotational element (called a wheel) with radial blades (like a propeller). When fluid flows through this wheel, it rotates due to fluid action and hence delivers electrical output. This output can be measured by a PLC (Programmable Logic Controller) or a microprocessor-based data acquisition system. Turbine flow meters measure high flows of non-abrasive liquid such as water, glycol, etc.

Advantages

Accuracy is excellent when compared to capacity-type instruments. Perfect response time and wide range of measurement; the display is clear and easy to read.

2. Coriolis Flow Meter

This type of flow meter is an advanced version of turbine flow meters and has a rotational element consisting of a series of rotating disks with radial blades (similar to turbine instruments). As in Turbine instruments, the measured fluid will also turn the whole rotational element, which will deliver electrical output. The measured fluid is either water, glycol, or any other non-abrasive liquid.

Advantages

Measurement accuracy is excellent when compared to capacity-type instruments. Fast response and wide range of Measure flow rate. The display is clear and easy to read; there are many options for installation (open channel, piping manifold, etc.)

3. Vortex Flow Meter

A vortex flowmeter, also known as a Pitot tube, uses an orifice plate (manifold) to measure the flow rate. This is done by measuring the static pressure and ambient temperature on both sides of the streamlines created at the nozzle plate. The pitot tube consists of a 2-port tube with nozzles at both ends. One nozzle is connected to the stream, and the other is left open in the air, which acts as a sensor for measuring velocity or absolute pressure difference.

Advantages

 Measurement accuracy is better than turbine flow meters but less accurate compared to Coriolis flowmeters. Fast response and wide range of linearity.

4. Weirs

This type of flow meter is based on the entry velocity head measurement, which can be calculated by dividing stream gradient (vertical) with horizontal distance between the weir crest and Measure flow rate. For example, if a stream has a continuous slope with a depth of 3 ft at 1 ft above the measuring point and horizontal distance between the weir crest and measuring point is 2 ft, then the entry velocity head will be 3/2 = 1.5 ft. Later this entry velocity head is converted into flow rate using given formulas

Advantages

Accuracy is excellent compared to turbine or vortex instruments but less accurate than Coriolis flowmeters. Measurement can be taken at any required point on the stream, which is not necessary to install a pitot tube or nozzle plate to take the size.

5. Electronic Totalizers

The electronic digital totalizer is a strong flow computer that can meet the needs of all types of liquid flow meters. This type of instrument makes electrical pulses corresponding to each unit volume of liquid passing through it. The advantage is that they have a built-in memory & digital display. These instruments can be used to measure higher flows, where other conventional devices cannot measure such flows without manual resetting.

Advantages

The measurement range is comprehensive and accurate for low to medium flow rates. 

6. Thermal Mass Flow Meter

This instrument is based on the density of the liquid, which can be obtained by knowing the mass flow rate and temperature difference between inlet and outlet streams. The thermal mass flow meter is a single element type of flow meter that uses a natural convection-based thermal differential to produce an electrical output and is not as accurate as the flow mentioned above.

Advantages

It has the broadest range of linearity. Measure flow rate can be improved by installing a small pump to create velocity on the outlet streamline. The measurement accuracy is perfect when compared to capacity-type instruments, and it also eliminates the need for refilling the flow meter.

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