Type and Model of Flow Meter
Measuring
the flow of liquids is a critical need in many industrial plants. In
some operations, the ability to conduct accurate flow measurements is so
important that it can make the difference between making a profit or
taking a loss. In other cases, inaccurate flow measurements or failure
to take measurements can cause serious (or even disastrous) results.
With
most liquid flow measurement instruments, the flow rate is determined
inferentially by measuring the liquid’s velocity or the change in
kinetic energy.
Velocity
depends on the pressure differential that is forcing the liquid through
a pipe or conduit. Because the pipe’s cross-sectional area is known and
remains constant, the average velocity is an indication of the flow
rate. The basic relationship for determining the liquid’s flow rate in
such cases is:
Q = V x A
where
Q = liquid flow through the pipe
A = sectional area of the pipe
Turbine Flowmeter
Turbine meters have found widespread use for accurate liquid and gas measurement applications. The unit consists of a multiple-bladed rotor mounted with a pipe, perpendicular to the liquid flow. The rotor spins as the liquid passes through the blades. The rotational speed is a direct function of the flow rate. Electrical pulses can be counted and totalized.Features :
Highly accurate and repeatable- Excellent long-term reliability Installation flexibility
- Economic and cost-effective solution for applications requiring high accuracy
- Only one moving part reduces maintenance cost
- A wide selection of materials A wide selection of output options
- There are much different manufacturing designs of turbine flow meters, but in general, they are all based on the same simple principle:
- If a fluid moves through a pipe and acts on the vanes of a turbine, the turbine will start to spin and rotate. The rate of spin is measured to calculate the flow.
Electromagnetic Flowmeter
An
electromagnetic flowmeter operates 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 and
the magnetic field is created by energized coils outside the flow tube.
The
voltage produced is directly proportional to the flow rate. Two
electrodes mounted in the pipe wall detect the voltage which is measured
by a secondary element. Electromagnetic flowmeters can measure
difficult and corrosive liquids and slurries, and they can measure flow
in both directions with equal accuracy. Electromagnetic flowmeters have a
relatively high power consumption and can only be used for electrical
conductive fluids like water.
Ultrasonic Flow Meter
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(one to transmit and the other to receive signal) are mounted in a case attached to one 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 be reflected in the receiver element, Fig. 10. 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 Doppler 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 to be used. Total weight, including the case, is 22 lb. A set of 4
to 20 mA output terminals permits the unit to be connected to a strip
chart recorder or another remote device.
Because
solids particles or entrained gases are required for measurement,
Doppler meters are not appropriate for clean liquids. In general,
Doppler flowmeters are less accurate than TOF flow meters, however, they
are less expensive
Time-of-travel(Transit-Time)
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. angle to the direction of liquid flow.
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. (Back to Meter Types Table)
Positive-Displacement Flowmeters
Although the positive-displacement flowmeter market is slightly larger than it was in 2001, it has been essentially flat for the past 10 years. Today, the PD flowmeter market is declining slightly. The main reasons the market is declining only slightly are the large installed base of PD meters, the large number of suppliers, and the ability of PD meters to measure high-viscosity liquids with high accuracy.PD meters are still widely used for downstream measurement of oil for custody transfer operations. Here they are being displaced by Coriolis meters, although they have a price advantage over Coriolis meters.
As the mechanism for the PD flow meters is simple, the PD flowmeters has uncomplicated structure and parts, compared to the other flow meters. It was designed to contain little liquid contact parts so that liquid stays in the chamber very shortly.
The PD flow meter driven by strong magnet coupling has a gear system mounted outside the measurement chamber, making it highly durable and easier to dismantle and assemble. As it does not contact liquid, it is highly durable and easy to dismantle and assemble.
Thermal Mass Flow Meter
Thermal
Mass Flow Meter is the instrument of choice for reliable and accurate
measurement of mass flows for various gases. It measures the mass flow
of gas based on constant temperature differential technology and is able
to measure gas flow in the range between 0 and 160 NMPS. Because
neither temperature nor pressure measurement is required, the MST series
reduces installation cost and vastly improves system accuracy.
The
meter is easily installed or retrofitted with minimum downtime and
provides superior, long-term process productivity and easy
serviceability. MST series can have either an inline sensor or an
insertion sensor.
The
inline sensor size ranges from 1” (25mm) to 12” (300mm) with either NPT
thread connection or flange connection. The insertion sensors are
available from 1” (25 mm) and above with the sensor mounting option of
either compression fitting or flange. The indicator/transmitter provides
a 4-20mA, pulse, RS- 485, HART, alarm, etc.
Coriolis Mass Flowmeter
Coriolis
Mass Flowmeter series is a mass flow meter that measures mass flow,
density and temperature of liquids, slurries, and gases. And it even
measures oil content in water. It has no moving parts and doesn’t
require any special device for installation.
And
it doesn’t require flow profile stabilization by means of flow
straightener or straight pipe run either upstream or downstream. The
wetted parts are made of high-grade stainless steel (SUS316L) and
therefore can be used for corrosive liquids.
The
mass flow-sensing element is composed of a pair of bent tubes,
vibrators and displacement sensors. The trick here is to detect the
Coriolis force applied on the tube by the flowing fluid inside the bent
oscillating tube. In order to do that, the vibrators vibrate the bent
tubes at the natural resonant frequency of the tubes.
When there’s a flow inside the tubes, the Coriolis force at work
distorts the vibration of the tubes. This distortion can be measured
using the displacement sensors. The amount of distortion is directly
proportional to the mass flow of the fluid inside the tube.
By
accurately processing the displacement, the accurate mass flow is
directly measured. Liquids, slurries, and gases can be measured. It
boasts strong immunity to noise, high accuracy, wide turndown ratio,
stability, and reliability.
More info and price please contact marketing@wmablog.com
