Transit Time Differential Ultrasonic Flow Measurement - How It Works

Ultrasonic flow meter, transducer and control unit
Courtesy Flexim

The measure of flow is a pervasive task in fluid process control. There are several differing technologies employed for measuring fluid flow, each with its own set of performance and application attributes that might make it the advantageous choice for a particular operation.

Ultrasonic flow measurement uses several methods for determining the average velocity of a fluid. One of those methods employs the difference in the transit times of ultrasonic pulses travelling with the flow direction and against the flow direction. The flow velocity of the media will offset the transit times between the flow and counterflow measurements. The measured difference in transit times can be used to determine average flow velocity and, with additional processing, mass flow.

Ultrasonic flow meters are accurate and provide repeatable results, making them suitable for custody transfer operations, as well as many other process control applications. Little maintenance is required and the units have no moving parts. Measurement instruments are available with in-line or clamp-on mounting, providing a high level of installation and application flexibility.

The short video below provides a clear explanation of how transit time difference measurement works. Share your flow measurement challenges and requirements with a product application expert, combining your process knowledge with their product expertise to develop effective solutions.

 

Use Nitrogen? How About Generating Your Own Supply?

Nitrogen is used extensively throughout industry

Nitrogen is utilized by industrial customers more than any other gas. In addition to being a part of every living thing on the planet, nitrogen is also the major component of atmospheric air at around 78% concentration.  It is incorporated as part of many compounds used to make a wide range of products. Nitrogen is also used as a cooling medium and as a means to isolate flammable or reactive compounds from oxygen.

There are several methods employed to generate or provide nitrogen, each with certain aspects making them advantageous to a certain range of applications. Convenience, reliability of supply, space, cost, energy consumption, purity, and a host of other factors can weigh on the decision for nitrogen supply.

Parker Balston, a globally recognized manufacturer of gas process equipment, authored a white paper making a case for considering in-house nitrogen generation for industrial processes. The article describes the three prevalent methods for producing highly purified nitrogen gas and compares their impact on the environment, as well as their suitability for users large and small.

The article, included below, is short and very informative, definitely worth reading. When considering your options for nitrogen supply, consider in-house production as a worthy alternative to the delivery of pressurized gas bottles. Share your requirements and challenges with a product application specialist, combining your process knowledge with their product expertise to develop an effective solution.

Comparison of Alternate Methods for Generating Nitrogen for Industrial Processing from Classic Controls, Inc.

Product Integrates Multiple Generator Condition Monitoring Functions in a Customized Unit

Multiple generator monitoring functions consolidated
in a single integrated console.
Courtesy E/One Utility Systems

Electric power generation involves enormous investment in fixed equipment operating at conditions requiring precision control of many variables. The availability of accurate real-time generator monitoring information can be the key element in maintaining precision equipment in good operating condition and avoiding downtime caused by failure.

E/One Utility Systems designs and manufactures a generator monitoring system combining multiple functions into a consolidated unit, fully engineered and coordinated for each application. Each customer can choose to incorporate functions as needed for their installation.

• Generator Auxiliary System
• Generator Gas Analyzer
• Generator Condition Monitor
• Generator Gas Dryer
• Auxiliary Systems

This flexible and cost efficient approach to gas monitoring and control systems for electric power generators capitalizes on the use of pre-engineered modules to reduce installation and on-site engineering burden.

More information is provided in the document below. Share your power generator monitoring and control challenges with product specialists and work together to develop effective solutions.

E/One Gas Station Integrates Multiple Generator Equipment Monitoring Functions from Classic Controls, Inc.

Asset Condition Monitoring Can Reduce Unplanned Outages and Improve Profitability

Model 3500 Rack Mount Monitoring Unit
Courtesy GE Bently Nevada

Lost industrial production and unplanned plant outages can be unbelievably costly.

Asset condition monitoring, as the name implies, is the process of continually monitoring a machine or piece of equipment with the intent to predict mechanical wear or failure point. Key indicators of failing equipment are changing values in vibration, noise, and temperature, all of which are measurable with the right equipment. Monitoring these variables, key indicators of machine operating health, provides valuable data which can be analyzed. By evaluating trends in the data, intelligent systems can provide useful information about the equipment and asset, such as early detection of possible faults or failures. The goal is to take preventative, less costly, measures, rather than clean up after an outright failure.

Continuously monitoring critical asset parameters such as vibration, temperature, speed, and numerous other condition indicators is a proven method for anticipating and preventing mechanical failures—proven in tens of thousands of industrial facilities around the world by delivering tangible benefits such as:

• Improved protection from catastrophic failures
• Better machinery reliability/availability
• Fewer process interruptions
• Enhanced maintenance/outage planning
• Lower maintenance and repair costs
• Longer intervals between outages
• Reduced insurance premiums

Implementation of asset condition monitoring is benefiting manufacturing plants and process industries such as chemical, petrochemical, pulp & paper, power generation, wind turbines, and oil & gas. Not only can it save money from protecting against unplanned outages, but condition monitoring also improves productivity, quality, and profitability.

GE's Bently Nevada 3500 Monitoring System provides continuous, online monitoring suitable for machinery protection and asset condition monitoring applications. It represents a capable and flexible system in a traditional rack-based design, offering numerous features and advantages not provided in other systems.

Share your equipment monitoring requirements and challenges, large and small, with application specialists. The combination of your process and facilities knowledge, with their product application expertise, will produce effective solutions.

Industrial Machinery and Asset Condition Monitoring from Classic Controls, Inc.

The Focus of 80 GHz Radar Level Instruments Applied to Bulk Solids

VegaPuls 69 - 80 GHz radar level transmitter for bulk solids
Courtesy VEGA

Level measurement of  bulk solids presents a range of challenges to process designers and operators. One instrument manufacturer, VEGA, has produced a video demonstrating a distinct advantage of utilizing 80 GHz radar level transmitters instead of those with lower operating frequencies. The demonstration shows actual instruments in use, along with displays of the actual output from the device. You should find it useful.

VEGA manufactures a wide range of instruments for measuring level, interface, density, and pressure for process control applications. Share your process measurement challenges with product application specialists, and combine your process knowledge with their product expertise to develop effective solutions.

Thermal Flowmeters with Constant Temperature Differential (∆T) Technology to Measure Mass Flow Rate of Air and Gases

Thermal Flow Meter
Sensor
Fox Thermal Instruments

Thermal flow meters use a constant temperature differential (∆T) technology to measure mass flow rate of air and gases. The thermal mass flow sensor consists of two Resistance Temperature Detectors (RTD’s). The sensor elements are constructed of a reference grade platinum wire wound around ceramic mandrels that are inserted into stainless steel or Hastelloy tubes.

The reference RTD measures the gas temperature. The instrument electronics
heat the mass flow sensor, or heated element, to a constant temperature and measures the cooling effect of the gas flow. The electrical power required to maintain a constant temperature differential is directly proportional to the gas mass flow rate. The microprocessor then linearizes this signal to deliver a linear 4 to 20mA signal.

One manufacturer, Fox Thermal Instruments, implements a

technology they call the Power Pro™ Sensor. Their sensor operates at a higher power level than other competitive thermal technologies, providing better response time and wider turndown. When compared to a typical differential pressure type flow meter, as shown to the right, the Power Pro™ Sensor offers better low flow or low end sensitivity. The Power Pro™ Sensor also provides exceptional accuracy at high velocities - up to 50,000 SFPM air.

The Fox DDC-Sensor™ is a new state of the art sensor technology used in the Fox Model FT1 Thermal Gas Flow Meter. The DDC-Sensor™, a direct digitally controlled sensor that is interfaced directly to the FT1 microprocessor for more speed and programmability.

Like the Power Pro™ Sensor, the DDC-Sensor™ accurately responds to changes in process variables (gas flow rate, pressure, and temperature) which are used by the microprocessor to determine mass flow rate, totalized flow, and temperature.

In addition to measuring flow, the DDC-Sensor™ provides a technology platform for calculating accurate gas correlations. The FT1 correlation algorithms allow the meter to be calibrated on a single gas in the factory while providing the user the ability to select other gases in the Gas-SelectX® gas menu. Fox’s Model FT1 with its DDC-Sensor™ and state-of-the-art correlation algorithms provide an accurate, multi-gas capable thermal flow meter for gas applications.

Thermal Mass Flowmeter and Temperature Transmitter from Classic Controls, Inc.

Radar Liquid Level Measurement Through a Sight Glass

Radar level control installed at tank sight glass
Courtesy VEGA

Level measurement, ubiquitous throughout processing operations, can be accomplished through the use of a number of different technologies. VEGA, a globally recognized innovator in level measurement, has authored a white paper outlining how radar level measurement instruments can be successfully employed when installed on tanks with sight glasses. The white paper is excerpted below, and you can access the full article and a wealth of application expertise by reaching out to an application specialist.

The balance of this article is excerpted from "Using radar sensors to measure liquid level through sight glasses", released by VEGA on 10/25/2016.

Vessels with sight glasses permit users to measure liquid level in a unique way: by mounting a radar sensor above the glass. Radar instruments emit microwaves that penetrate the glass, reach the product inside, and reflect through the glass back to the sensor. This eliminates two major expenses because users are spared from retrofitting a tank to accommodate a sensor and can continue running a process during installation. Functionally, nothing changes as users can simply move the sensor for a moment to look through the glass and see what’s happening inside a vessel.

Challenges to radar level measurement through sight glass

Any radar sensor can measure liquid level through a sight glass, but what happens after a signal penetrates glass varies depending on the sensor. Glasses are often welded, bolted or clamped directly onto a vessel wall or roof with a circular flange, while others are mounted on a nozzle. Radar sensors with a transmission frequency of 26 GHz release wide beams that contact the sides of the flange, the nozzle, and sometimes the roof of the vessel itself. This creates noise at the top of the output, especially on taller nozzles, forcing operators to leave empty space inside a tank to make a clear distinction between the signal received from the vessel and the signal received from the product.

Further complicating the use of 26 GHz sensors with sight glasses is the fact that most sight glasses are installed at a natural slope in the tank. Angled glasses narrow the path to the liquid, increasing the degree of difficulty in setting up a sensor so the beam is perpendicular to the product. Perpendicularity is important because it’s in direct relationship to the strength of the signal the sensor receives. However, to minimize the small signals that bounce from the glass to back the sensor, it’s recommended that users pair a 26 GHz radar sensor with a sight glass installed at a 45° angle. This forces users to choose between a strong signal from the product accompanied by reflections from the glass or a weak signal from the product and no reflections for the glass. Neither scenario is ideal.

Enhanced signal focusing makes all the difference

The problem of noise from fittings and narrow paths can be solved by installing a radar sensor that operates at a higher transmission frequency and produces a more focused signal. The VEGAPULS 64, for example, has a frequency of 80 GHz and can emit a beam angle of only 3°. 26 GHz sensors, on the other hand, emit beam angles of approximately 10°. A narrow beam angle misses the sides of the flange and the nozzle, silencing signal noise. That same focused beam can travel a tight path to the product without sacrificing signal strength. Finally, 80 GHz radar sensors don’t need sight glasses at extreme angles to minimize reflected signals, as a sight glass installed at a 5-10° angle will do.

Other benefits of external level instruments

All this is welcome news to processes where sight glasses already exist and is also noteworthy for those struggling with level measurement technology in traditional tanks. Users in the latter camp may find it more economical to install an external radar level sensor and a sight glass than a new internal instrument because removing a sensor from the interior of a vessel presents users with several benefits. In applications involving harsh, caustic liquids, there’s no risk of the product damaging the sensor with a quick splash or corroding it over time through buildup. This saves users in routine maintenance costs, and lack of exposure extends a sensor’s life. Users can mount a radar sensor above such tanks, and the emitted microwaves penetrate the glass and reliably measure the harsh liquid inside.

External access to a level measurement instrument is also useful for a quick repair or recalibration. With the sensor on the outside of the vessel, users can keep the plant’s process moving while they perform routine maintenance. If a problem arises with an instrument inside of a tank, that particular tank—or worse, an entire line—might have to be shut down, potentially leading to thousands of dollars in lost production. What company can afford that?

Summary

In conclusion, radar sensors of any transmission frequency can be mounted above sight glasses for accurate, non-contact level measurement. Separation from the product helps preserve sensors, and the instruments are easy to access when calibration and maintenance are necessary. When researching their options, users should consider 80 GHz sensors because they emit focused radar beams that take a narrow path to the liquid and fewer signals are reflected by flanges and mounting nozzle interiors. Given radar technology’s accuracy and reliability, and all that can go wrong if an internal level measurement fails, a radar sensor mounted above a sight glass offers nothing but advantages.