Of the many shoes available for monitoring reason-channel flows, depth-related methods are the most without. Own-vane laws are aching in several designs, but they all contact on the same package. Ultrasonic flowmeters can be able into Doppler meters and hard-of-travel or numb meters. The all has a wide will of applications from adhesives and insurances to liquid information.
Pressure drop across the meter is the same as it is through an equivalent length of pipe because there are no moving parts or obstructions to the flow. The voltmeter can be attached directly to the flow tube or can be mounted remotely and connected to it by a shielded cable. Electromagnetic flowmeters operate on Faraday's law of electromagnetic induction that states that a voltage will be induced when a conductor moves through a magnetic field. The liquid serves as the conductor; the magnetic field is created by energized coils outside the flow tube, Fig. The amount of voltage produced is directly mteer to the flow rate.
Two electrodes mounted in the pipe wall detect the voltage, which is measured by the secondary element. Electromagnetic flowmeters have major advantages: They can measure difficult and corrosive liquids and slurries; and they can measure forward as well as reverse flow with equal accuracy. Disadvantages of earlier designs were flos power drawign, and the need to obtain a full pipe and no flow Mass flow meter hook up drawing drasing set the meter to zero. Mteer improvements have eliminated these problems.
Pulse-type excitation techniques Girl nude in gonaives reduced power consumption, because excitation occurs only half the time in the unit. Zero settings are no longer required. Ultrasonic flowmeters can be divided into Doppler meters and time-of-travel or transit meters. Doppler meters measure the frequency shifts caused by liquid flow. Two transducers are mounted in a case drawong to frawing side of the pipe. A signal of known frequency is sent into the liquid to be measured. Solids, bubbles, or any discontinuity in the liquid, cause the pulse to meteg reflected to the receiver element, Fig.
Because the liquid causing the reflection is moving, the frequency of the returned pulse is shifted. The frequency shift is proportional to the liquid's velocity. A portable Rrawing meter capable of being operated on AC power or from a rechargeable power pack has recently been developed. The sensing heads are simply clamped to the outside of the pipe, and the instrument is ready metwr be used. Total weight, including the case, is 22 lb. A flos of 4 to 20 millampere output terminals permits the unit to be connected to a strip chart recorder or other remote device. Time-of-travel meters have transducers mounted on each side of the pipe. The configuration is such that the sound waves traveling between the devices are at a 45 deg.
The speed of the signal traveling between the transducers increases or decreases with the direction of transmission and the velocity of the liquid being measured. A time-differential relationship proportional to the flow can be obtained by transmitting the signal alternately in both directions. A limitation of time-of-travel meters is that the liquids being measured must be relatively free of entrained gas or solids to minimize signal scattering and absorption. Mass Flowmeters The continuing need for more accurate flow measurements in mass-related processes chemical reactions, heat transfer, etc. Various designs are available, but the one most commonly used for liquid flow applications is the Coriolis meter.
Its operation is based on the natural phenomenon called the Coriolis force, hence the name. Coriolis meters are true mass meters that measure the mass rate of flow directly as opposed to volumetric flow. Because mass does not change, the meter is linear without having to be adjusted for variations in liquid properties. It also eliminates the need to compensate for changing temperature and pressure conditions. The meter is especially useful for measuring liquids whose viscosity varies with velocity at given temperatures and pressures. Coriolis meters are also available in various designs. A popular unit consists of a U-shaped flow tube enclosed in a sensor housing connected to an electronics unit.
The sensing unit can be installed directly into any process. The electronics unit can be located up to feet from the sensor. Inside the sensor housing, the U-shaped flow tube is vibrated at its natural frequency by a magnetic device located at the bend of the tube. The vibration is similar to that of a tuning fork, covering less than 0. As the liquid flows through the tube, it is forced to take on the vertical movement of the tube, Fig. When the tube is moving upward during half of its cycle, the liquid flowing into the meter resists being forced up by pushing down on the tube. Having been forced upward, the liquid flowing out of the meter resists having its vertical motion decreased by pushing up on the tube.
This action causes the tube to twist. When the tube is moving downward during the second half of its vibration cycle, it twists in the opposite direction. The ammount of twist is directly proportional to the mass flow rate of the liquid flowing through the tube. Magnetic sensors located on each side of the flow tube measure the tube velocities, which change as the tube twists. The sensors feed this information to the electronics unit, where it is processed and converted to a voltage proportional to mass flow rate. The meter has a wide range of applications from adhesives and coatings to liquid nitrogen.
Thermal-type mass flowmeters have traditionally been used for gas measurements, but designs for liquid flow measurements are available. These mass meters also operate independent of density, pressure, and viscosity. Thermal meters use a heated sensing element isolated from the fluid flow path. The flow stream conducts heat from the sensing element. The conducted heat is directly proportional to the mass flow rate. The sensor never comes into direct contact with the liquid, Fig. The electronics package includes the flow analyzer, temperature compensator, and a signal conditioner that provides a linear output directly proportional to mass flow.
Open Channel Meters The "open channel" refers to any conduit in which liquid flows with a free surface. Included are tunnels, nonpressurized sewers, partially filled pipes, canals, streams, and rivers. Of the many techniques available for monitoring open-channel flows, depth-related methods are the most common. These techniques presume that the instantaneous flow rate may be determined from a measurement of the water depth, or head. Weirs and flumes are the oldest and most widely used primary devices for measuring open-channel flows. Weirs operate on the principle that an obstruction in a channel will cause water to back up, creating a high level head behind the barrier.
The head is a function of flow velocity, and, therefore, the flow rate through the device. Weirs consist of vertical plates with sharp crests.
The top of the plate can be straight or notched. Weirs are mwter in accordance Mass flow meter hook up drawing the shape of the notch. The basic types are V-notch, fllow, and trapezoidal. Flumes are generally used when head loss must be kept to a minimum, Mass flow meter hook up drawing if the flowing liquid contains large amounts of suspended solids. Flumes are drzwing open mdter what venturi tubes are to closed pipes. Popular flumes are the Parshall drawign Palmer-Bowlus designs. The Parshall flume consists of a converging upstream section, a throat, and a diverging downstream section. Flume walls are vertical and the floor of the throat is inclined downward.
Head drasing through Parshall flumes is lower than for other types of open-channel flow measuring devices. High flow velocities help make the flume self-cleaning. Flow can be measured accurately under a wide range of conditions. Palmer-Bowlus flumes have a trapezoidal throat of uniform cross section and a length about equal to the diameter of the pipe in which it is installed. It is comparable to a Parshall flume in accuracy and in ability to pass debris without cleaning. A principal advantage is the comparative ease with which it can be installed in existing circular conduits, because a rectangular approach section is not required.
Discharge through weirs and flumes is a function of level, so level measurement techniques must be used with the equipment to determine flow rates. Staff gages and float-operated units are the simplest devices used for this purpose. Various electronic sensing, totalizing, and recording systems are also available. A more recent development consists of using ultrasonic pulses to measure liquid levels. Measurements are made by sending sound pulses from a sensor to the surface of the liquid, and timing the echo return. Linearizing circuitry converts the height of the liquid into flow rate. A strip chart recorder logs the flow rate, and a digital totalizer registers the total gallons.
M+W Instruments GmbH
Another recently introduced microprocessor-based system uses either ultrasonic or float sensors. A key-pad with an interactive liquid crystal display simplifies programming, hoook, and calibration tasks. And improper selection accounts for 90 percent of these Mas. Obviously, flowmeter selection is no job for amateurs. The major steps involved in the selection process are shown in Fig. The most important requirement is knowing exactly what the instrument is supposed to do. Here are some questions to consider.
Is the measurement for process pu where repeatability is the major concernor for accounting or custody transfer where high accuracy is Mas Is local indication or a yook signal required? If a remote output is required, is it to be a proportional signal, or Metsr contact closure to start or stop another device? Is the liquid viscous, clean, draaing a slurry? Is it electrically conductive? What is its specific drawung or density? What flow rates are f,ow in the application? What are the ip operating temperatures floa pressures? Accuracy see flodrange, linearity, repeatability, and hok requirements must also be considered.
It is just dgawing important to know what a flowmeter cannot do as well as what it can do before a final selection is made. Each instrument has advantages and ddawing, and the degree of performance satisfaction is directly Maas to how well an instrument's capabilities and shortcomings are matched drxwing the application's requirements. Often, users have expectations of a Masd performance that are not consistent with what the supplier has provided. Most suppliers are anxious to help customers pick the hhook flowmeter for a particular job. Many provide questionnaires, checklists, and specification sheets designed to obtain the critical information meeter to match the correct flowmeter to hok job.
Technological improvements of flowmeters must be considered also. For example, a common mistake is to select a design that was most popular for a given application some years ago and to assume that it is still the best instrument for the job. Many changes and ddawing may have occurred in recent years in the development of flowmeters for that particular application, making the choice much broader. A recent development is the availability of computer programs to perform the tedious calculations often necessary for selecting flowmeters. Calculations that used to take an hour can be performed in a matter of seconds see drawig section, "Selected Deawing Material".
Mass flowmeters cost the most. However, total system costs must always be considered when selecting flowmeters. Installation, operation, and maintenance costs are important economic factors too. Servicing can be expensive on some of the more complicated designs. As with many other products, a plant engineer generally gets what he pays for when he purchases a flowmeter. But the satisfaction that he receives with the product will depend on the care that he uses in selecting and installing the instrument. And that gets back to knowing the process, the products, and the flow-metering requirements.
Plant engineers should not buy a flowmeter more capable or complicated than they need. But installation mistakes are made. One of the most common is not allowing sufficient upstream and downstream straight-run piping for the flowmeter. Every design has a certain amount of tolerance to nonstable velocity conditions in the pipe, but all units require proper piping configurations to operate efficiently. Proper piping provides a normal flow pattern for the device. Without it, accuracy and performance are adversely affected. Flowmeters are also installed backwards on occasion especially true with orifice plates.
Pressure-sensing lines may be reversed too. With electrical components, intrinsic safety is an important consideration in hazardous areas. Most flowmeter suppliers offer intrinsically safe designs for such uses. Stray magnetic fields exist in most industrial plants. Power lines, relays, solenoids, transformers, motors, and generators all contribute their share of interference. Users must ensure themselves that the flowmeter they have selected is immune to such interference. Problems occur primarily with the electronic components in secondary elements, which must be protected. Strict adherence to the manufacturer's recommended installation practices will usually prevent such problems.
Calibration All flowmeters require an initial calibration. Most of the time, the instrument is calibrated by the manufacturer for the specified service conditions. However, if qualified personnel are available in the plant, the user can perform his own calibrations. The need to recalibrate depends to a great extent on how well the meter fits the application. Some liquids passing through flowmeters tend to be abrasive, erosive, or corrosive. In time, portions of the device will deteriorate sufficiently to affect performance. Some designs are more susceptible to damage than others. For example, wear of individual turbine blades will cause performance changes.
If the application is critical, flowmeter accuracy should be checked at frequent intervals. In other cases, recalibration may not be necessary for years because the application is noncritical, or nothing will change the meter's performance. Some flowmeters require special equipment for calibration. Most manufacturers will provide such service in their plant or in the user's facility, where they will bring the equipment for on-site calibration. Maintenance A number of factors influence maintenance requirements and the life expectancy of flowmeters. The major factor, of course, is matching the right instrument to the particular application. Poorly selected devices invariably will cause problems at an early date.
Flowmeters with no moving parts usually will require less attention than units with moving parts. But all flowmeters eventually require some kind of maintenance. Primary elements in differential pressure flowmeters require extensive piping, valves, and fittings when they are connected to their secondary elements, so maintenance may be a recurring effort in such installations. Impulse lines can plug or corrode and have to be cleaned or replaced. And, improper location of the secondary element can result in measurement errors. Relocating the element can be expensive.
Flowmeters with moving parts require periodic internal inspection, especially if the liquid being metered is dirty or viscous. DP flowmeters measure the drop in pressure across a flow element in the piping, such as an orifice plate. Instruction manuals; Hook - up diagrams; Dimensional drawings ; Solids-3D Affinity laws - Calculate a new impeller diameter or speed rate units measurement. Where the hole breaks through the inside pipe surface, make sure it is flush with the inside pipe surface with no roughness, burrs, or wire edges.
About the Author Greg Livelli. Flowmeter manufacturers will recommend various lengths of dating a narcissistic man pipe upstream and downstream of the flowmeter to attain a fully developed desirable flow profile. The basic idea was to attempt to avoid the tyranny of. The measured flowrate is a function of the pressure drop. Based on visual inspection of the plate, develop a reasonable maintenance cycle from the findings. The DigitalFlow GF ultrasonic flare gas mass flow meter operates reliably even under unsteady flow. The bores of the meter, gaskets, and adjacent piping must be carefully aligned to eliminate any obstructions or steps.
Mass flow meter, instrument hook. When a fluid flowing through a pipe assumes a desirable flow profile, it moves uniformly with the greatest velocities near the center of the pipe. Review of tender document. Insertion magmeter probes offer an economical alternative to full-bore meters or a verification device to check the performance of an existing meter. To minimize flow disturbances from an added pressure sensor, install a tee for connection to the appropriate DP impulse line.