Non-Contact Area Velocity Flow Measurement Using Advanced Laser Doppler Technology

Non-contact flow measurement in open channels is
effectively conducted with laser doppler technology
Image courtesy Teledyne ISCO

An effective way to measure liquid flow in open channels employs a combination of non-contact Laser Doppler Velocity technology and non-contact Ultrasonic Level technology. Teledyne ISCO manufactures a variant of their LaserFlow non-contact flow meter that incorporates both velocity and depth sensors into a single compact unit. The sensor uses advanced technology to measure velocity with a laser at single or multiple points below the surface of the water or wastewater stream.

An ultrasonic level sensor provides the depth of the flow, and the system determines a sub-surface point at which to measure velocity. The sensor then focuses the laser at the designated point and measures the frequency shift of the returned light.

This sensor is ideal for a broad range of wastewater monitoring applications and is compatible with readily available flow meters.

With optional continuous wave Doppler Ultrasonic Area Velocity technology flow measurement continues without interruption even while submerged.

A specially designed mounting bracket enables deployment of the sensor in a manner that permits removal from street level, avoiding the risk and expense of confined space entry. A variety of communication options enable programming and data retrieval from a remote location as well. Built-in diagnostic tools simplify installation, maintenance, and advanced communication options reduce site visits.

The sensor provides excellent system versatility across a wide variety of industrial applications to manhole installations, with many configuration options providing the flexibility to measure flow in most open channel applications.

Depending on your application needs, the device can be programmed to take velocity measurements at single or multiple points below the water's surface, producing an accurate mean velocity reading.

In applications where the level measurement point of the built-in ultrasonic and the measurement point of the laser velocity are of different elevations, such as a freefalling outfall or drop manhole, the remote ultrasonic option can be used so that both measurement points reference the same elevation.

During submerged conditions, the optional bottom-mounted area velocity sensor seamlessly takes over the flow rate measurement. The sensor provides ultrasonic Doppler velocity measurement and Differential Pressure level measurement. This option measures flow in the pipe/channel. By measuring velocity over a large area, the ultrasonic Doppler technology provides more accurate flow measurement during submerged conditions.

For redundant flow measurement at critical monitoring sites, a unique flexibility is added by an optional sensor which is mounted at the bottom of the pipe. This sensor provides redundant velocity, level, and flow data from the same site as the device.

Following initial installation and adjustment, the sensor can be installed or removed as needed without manhole entry in most situations, using the optional sensor retrieval arm to grasp the handle. The handle's simple yet effective locking mechanism holds the sensor securely in place, and is easy to engage and release from above ground.

Share your open channel flow measurement challenges with measurement instrumentation experts. Leverage your own knowledge and experience with their product application expertise to develop an effective solution.

Non-Contact Open Channel Flow Measurement from Instrument Specialties, Inc.

Sight Flow Indicators

Sight flow indicators give operators a rapid and direct
means of verifying process flow.
Image courtesy Clark Reliance - Jacoby-Tarbox

Industrial process operations involving fluids benefit greatly from advanced instrumentation and measure, but there may be instances where a visual confirmation or assessment of fluid flow is useful or necessary. In those cases, a direct reading sight flow indicator is just the thing needed to fill the requirement.

The sight flow indicator is essentially a clear window or tube with an encasement and appropriate connections that facilitate its installation into a process piping system. It is installed in a manner that provides an operator visual access to the inside of the piping at that location. Further details about construction materials, armoring, and more will round out the product selection that best accommodates the industrial environment, the media, and the visual inspection needs.

Jacoby-Tarbox manufactures a range of  fluid processing and measurement products, including sight flow indicators, for industrial use. Their sight flow indicators, available in a broad range of line sizes and connections, enable a process operator to get that all important visual inspection of liquid or gaseous media flow in real time. The presence, color and character of the media can be assessed visually through the flow indicator, delivering visual confirmation of some targeted aspect of the process.

Share your process flow and level measurement challenges with instrumentation specialists, leveraging your own knowledge and experience with their product application expertise to develop an effective solution.

Sight Flow Indicators With Flanged Connection from Instrument Specialties, Inc.

Two-Wire vs. Four-Wire Transmitter For Analog Process Signals - What to Consider?

I/O modules are an integral part of process signal connectivity.
Image courtesy of Acromag

Transmitters are everywhere in process control. They take a sensor output signal,amplify and condition it, then send it to monitoring and decision making devices. The most common analog electrical signal used for transmitting process control signals is a 4-20 mA (milliampere) current flow. It has succeeded in its adoption for a number of reasons, not the least of which are its resistance to interference and ability to transmit a signal across a substantial length of cable.

Aside from the sensor connection, there are two basic wiring schemes for these devices. The simplest employs just two conductors to transmit the signal and coincidentally provide operating power for the transmitter electronics. This type of transmitter is commonly referred to as a "loop powered" or "two-wire" device. A DC power supply, typically 24 volts, is wired in series with the 4-20 mA output signal and the transmitter derives its operating power from this source. Loop powered devices generally consume very little power, but process designers must consider the total resistance imposed on the loop by all connected devices. The cable, unless the length is monstrous, poses a measurable but comparatively small resistance. Careful consideration should be given to the resistance imposed by receiving devices, especially if there are several in series, receiving the loop signal. The output voltage of the power supply and the maximum tolerable voltage of the connected devices will serve as limiting factors on loop instrument quantity. Where they can be applied, two-wire transmitters offer a straight forward solution for delivery of analog process measurement signals.

A "four-wire" transmitter gets its name from, you guessed it, the two pairs of wires used to provide operating power and a signal transmission path. Provided with a separate power source, possibly even 120 volts AC, this transmitter type will often be found in applications where the sensor may have power requirements that cannot be met with the limitations inherent in the loop powered device. While it may seem that the separate power supply negates the need to consider total resistance load on the signal loop, this is not the case. The signal loop still will be limited by the DC power supply that serves as the driving force of the loop.

In many cases, the question of "two-wire or four-wire" will be answered by the transmitter manufacturer. Since the two-wire scheme is a less burdensome installation, it may be the only product offering when a suitable device can be designed for an application. That said, a diligent search will probably find two and four-wire versions of transmitters for almost every application.

What are some decision making guidelines?

• Some types of transmitters have sufficiently high power requirements that they cannot be loop powered. In this case, four-wire may be the only option.
• For low resistance loads, use 2 wire transmitters for a simpler installation.
• Allow some headroom in the loop resistance to accommodate at least one added receiving device in the future. For example, a temperature signal may serve as an input to a controller now, but need to service a recording device potentially added in the future.
• Distance should not be mindlessly overlooked, but is generally not a limiting factor, as most installations would be compatible with the distance limitations for two- or four-wire device output signals.
• When signal transmission distances become unwieldy, due to cabling costs or other factors, consider a wireless transmitter instead of a wired device.

An important aspect of applying 4-20 mA signal loops is to maintain the capability to add another receiving device to the circuit. The use of information in the form of process signals has been growing for a long time and is likely to continue. It is certainly easier to wire an additional device into an existing loop, than to install an additional sensor, transmitter, power supply, and cabling to accommodate the additional device.

Share your process measurement requirements and challenges with process instrumentation experts, leveraging your own process knowledge and experience with their product application expertise to develop complete and effective solutions.


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Make Good Use of Technical Sales Representatives

Technical sales representatives bring outside expertise

Process and control equipment is most often sold with the support of sales engineers working for the local distributor or representative. Realizing what these specialists have to contribute, taking advantage of their knowledge and talent, will help save time and cost, contributing to a better project outcome.

Consider these contributions:

Product Knowledge: Sales engineers, by the nature of their job, are current on new products, their capabilities and their proper application. Unlike information available on the Web, sales engineers get advanced notice of product obsolescence and replacement. Also, because they are exposed to so many different types of applications and situations, sales engineers are a wealth of tacit knowledge that they readily share with their customers.

Experience: As a project engineer, you may be treading on fresh ground regarding some aspects of your current assignment. You may not have a full grasp on how to handle a particular challenge presented by a project. Call in the local sales person - there can be real benefit in connecting to a source with past exposure to your current issue.

Access: Through a technical sales engineer, you may be able to look “behind the scenes” with a particular manufacturer and garner important information not publicly available. Sales reps deal with people, making connections between customers and manufacturer's support personnel that may not normally be public facing. They make it their business to know what’s going on with products, companies, and industries.

Of course, sales engineers will be biased. Any solutions proposed are likely to be based upon the products sold by the representative. But the best sales people will share the virtues of their products openly and honestly, and even admit when they don’t have the right product. This is where the discussion, consideration and evaluation of several solutions become part of achieving the best project outcome.

As an engineer who designs or manufactures a product or process, it's highly recommended you develop a professional, mutually beneficial relationship with a technical sales expert, a problem solve. Look at a relationship with the local sales engineer as symbiotic. Their success, and your success, go hand-in-hand.

Measuring Flow in Open Channels

Parshall flume at a water treatment facility
Courtesy Tracom Fiberglass Products

Industrial, municipal, and commercial processing operations can employ open channels as a means to direct and transport liquids. Open channel flow is technically fluid passing through a conduit with a free surface. The mechanics of this type of flow are well characterized, allowing volumetric flow rate to be determined using a single measurement of liquid depth as it passes through a channel of known shape. These shaped portions of the fluid transport system are known as flumes.

There are a number of different flume types used for flow measurement, each with its own name, shape, and application characteristics. One of the most common is the Parshall flume, named after its inventor. In its simplest application, the Parshall flume directs liquid flow through a narrowed throat. The depth of the liquid is measured at a designated point along the flume. Using known flow characteristics for the flume shape and size, volumetric flow rate can be calculated using the depth measurement.

Flumes are widely used in wastewater treatment plants, irrigation, and other applications where flow measurement is needed in an open channel. The flume can be constructed of almost any suitable material, but must be dimensionally correct and stable. Fiberglass is often a material of choice because of its weight, corrosion resistance, cost, and ease of installation. A fiberglass flume can be prefabricated with dimensional precision, shipped to the installation site and essentially dropped in place as a complete unit. Numerous options are available with fiberglass flumes to accommodate every installation requirement.

• Ultrasonic level sensor mounting brackets
• Bubble tubes
• Sample tubes
• Submerged probe cavities
• Stilling wells (attached and detached)
• Staff gauges
• Removable probe holders
• Inlet and outlet end adapters
• Pipe stubs
• Flanged end connections
• Flow straighteners
• Fiberglass grating
• Inlet and outlet wingwalls
• Multi-piece construction
• Nesting
• Chemically resistant gel coal

Share your open channel flow measurement challenges and requirements with an application specialist for recommendations on complete flow measurement solutions.

Advanced Laser Doppler Technology for Non-Contacting Area Velocity Flow Measurement

Laser Doppler Technology
for Non-Contacting Area
Velocity Flow Measurement
(by Teledyne ISCO)

A new velocity sensor remotely measures flow in open channels with non-contact Laser Doppler Velocity technology and non-contact Ultrasonic Level technology. The sensor uses advanced technology to measure velocity with a laser beam at single or multiple points below the surface of the wastewater stream.

An ultrasonic level sensor is used to measure the level and then determines a sub-surface point to measure velocity. The sensor then focuses its laser beam at this point and measures the frequency shift of the returned light.

This sensor is ideal for a broad range of wastewater monitoring applications and is compatible with readily available flow meters.

With optional continuous wave Doppler Ultrasonic Area Velocity technology flow measurement continues without interruption even while submerged.

With a specially designed mounting bracket the sensor can be deployed and removed from street level,  avoiding the risk and expense of confined space entry. A variety of communication options enable programming and data retrieval from a remote location as well. Built-in diagnostic tools simplify installation, maintenance, and advanced communication options reduce site visits.

The sensor provides excellent system versatility across a wide variety of industrial applications to manhole installations, with many configuration options providing the flexibility to measure flow in most open channel applications.

Depending on your application needs, the device can be programmed to take velocity measurements at single or multiple points below the water's surface, producing an accurate mean velocity reading.

In applications where the level measurement point of the built-in ultrasonic and the measurement point of the laser velocity are of different elevations, such as a freefalling outfall or drop manhole, the remote ultrasonic option can be used so that both measurement points reference the same elevation.

During submerged conditions, the optional bottom-mounted area velocity sensor seamlessly takes over the flow rate measurement. The sensor provides ultrasonic Doppler velocity measurement and Differential Pressure level measurement. This option measures flow in the pipe/channel. By measuring velocity over a large area, the ultrasonic Doppler technology provides more accurate flow measurement during submerged conditions.

For redundant flow measurement at critical monitoring sites, a unique flexibility is added by an optional sensor which is mounted at the bottom of the pipe. This sensor provides redundant velocity, level, and flow data from the same site as the device.

Following initial installation and adjustment, the sensor can be installed or removed as needed without manhole entry in most situations, using the optional sensor retrieval arm to grasp the handle.

The handle's simple yet effective locking mechanism holds the sensor securely in place, and is easy to engage and release from above ground.

Advanced Laser Doppler Technology for Non-Contacting Area Velocity Flow Measurement from Instrument Specialties, Inc.

For more information contact:

Instrument Specialties Inc.
3885 St. Johns Parkway
Sanford, FL 32771
phone 407.324.7800
fax 407.324.1104
e-mail: offices@isisales.com