Working Principle of Paddle Wheel Flow Meters

Paddle wheel flow meters consist of three primary components: the paddle wheel sensor, the pipe fitting and the display/controller. The paddle wheel sensor consists of a freely rotating wheel or impeller with embedded magnets which is perpendicular to the flow and will rotate when inserted in the flowing medium.

Principle of Paddle Wheel Flow Meters

As the magnets in the blades spin past the sensor, the paddle wheel meter generates a frequency and voltage signal which is proportional to the flow rate. The faster the flow the higher the frequency an
d the voltage output.

The paddle wheel meter is designed to be inserted into a pipe fitting, either ‘in-line’ or insertion style. These are available with wide range of fittings styles, connection methods and materials such as PVDF, polypropylene, and stainless steel. Similar to turbine meters, the paddle wheel meter require a minimum run of straight pipe before and after the sensor.

Flow displays and controllers are used to receive the signal from the paddle wheel meter and convert it into actual flow rate or total flow values. The processed signal can be used to control the process, generate an alarm, send signals to external etc.

Paddle wheel flow meters (also known as Pelton wheel sensors) offer a relatively low cost, high accuracy option for many flow system applications, typically with water or water like fluids.

Paddle Wheel Flow Meter Advantages

Low cost solution with high flow system accuracy
Easy to install and operate, resulting in a low cost of ownership
No pressure drop making it ideal for gravity flows
Insertion flow meter design lowers installation and maintenance costs

Paddle Wheel Flow Meter Limitations

Paddle wheel meters work best with clean fluids as particulates can prevent the paddle from spinning properly
Not suitable for gases
Requires a turbulent flow profile (consistent fluid velocity across the pipe diameter) for accuracy
Requires a straight run of pipe before and after the flow meter to allow swirl patterns in the flow stream to dissipate
Paddlewheel meters may not function properly with high viscosity fluids where the flow profile is laminar
The pipe must be full; any air in the line may lead to inaccuracies

Typical applications for paddle wheel flow meters include the accurate measurement of preset fluid volumes in dispensing systems, control of chemical metering pump output, flow verification, irrigation systems and alerting users to flow rate increases or decreases outside a programmed range.

Comments

Ferrules and Cross Ferruling

Ferrules are identification labels provided for every wire terminations in an instrument, equipment, or electrical/instrumentation control panels. These tube-shaped sleeves can be inserted easily on each individual wire in a multi-core cable. In earlier days fixed digits/letters are used as ferrules, but now Instrumentation engineers/technicians prints out desired ferrules by using a ferrule printing machine. Typical Ferrule The numbers/ letters on the ferrules will be given as per the approved electrical hook up or loop diagrams. This helps technicians to easily identify a particular loop/wiring from a series of terminal blocks and to troubleshoot the desired terminal connection. Separate numbers on the ferrules distinguish the positive and negative polarities of wires, thus ensure the polarity protection of the instrument. Cross Ferruling As a wire is connected on its both ends, it is quite useful to use a cross reference method for wire identification. Unlike normal ferru...

What is a Torbar? – Averaging Pitot Tubes

The Torbar is employed for flow measurement of liquids, gases, or steam in circular, square, or rectangular section ducts for large flow rates. The Torbar is an insertion type multi-port self-averaging primary sensor for flow measurement. Torbar TORBAR is a set of Pitot tubes mounted on a bar across the pipeline with no moving parts. An averaging Pitot tube is a technology, while TORBAR is a manufacturing brand name. There are several brands available in the market with VERABAR, ANNUBAR, etc. Averaging Pitot Tube Principle Purpose Averaging Pitot tube can be employed when the average velocity of the flow profile, rather than the velocity in a specific point in the cross-section is desired. Averaging Pitot Tubes Principle It measures the differential pressure between the static pressure tap and the tap of full pressure of a stream. Thus such magnitude of differential pressure is directly proportional to the square of the flow rate. Working The TORBAR is designed in such a way that ...

Thermowell Insertion and Immersion Length

The thermowell is the industrial housing for temperature elements like RTD or thermocouple or temperature gauges. Thermowell is directly exposed to process fluid/media. Inside the thermowell, element/gauge is installed. Thermowell transfers the heat to the temperature element. Depending upon the element type, the fluid temperature can be known. So Thermowell protects the temperature element against harsh conditions and process fluid. It enables removal of the temperature element for replacement, repair, or testing without affecting the process system. Generally, thermowells are provided with all-temperature Elements like RTD or Thermocouple or temperature gauge. A few exceptions would be bearing RTD, skin type thermocouple, air duct thermometer, etc where thermowell is not applicable / required. When the thermowell assembly is inserted into the pipe, it is subjected to vibration. This vibration is caused by vortices to be generated alternately on either side of the thermowell. The...

TILI Automation

Search This Blog