Welcome to the February 2015 issue
of fLowdown - a quarterly Newsletter from
Titan Enterprises Ltd. written to keep you
informed about the latest technological developments, applications advances and
breaking news in the field of flow measurement.

If a particular feature interests you, do not hesitate to contact us or follow the link for further information. We welcome your feedback.

Trevor Forster (Managing Director)

 

Trevor's
Technical Tip

Trevor Forster is Managing Director of Titan Enterprises. His experience in fluid handling dates back to the mid 1960's when he started working on rotating seals and flowmeter design for third party clients. Drawing upon over 40 years of using innovative design and production techniques to produce elegant flow metering solutions for organisations around the globe, in this feature - Trevor offers you a useful technical tip.

Flowmeter Terms - Cutting out the 'Marketing Speak'

The following explanation of terms commonly associated with flow metering are not necessarily the strict definitions to be in published standards but are more an attempt to describe the terms in more accessible ‘less commercial’ language.

Liquid flow meter performance can be expressed in several ways and within the industry there is some imaginative specification writing. What is meant by performance? What does a full scale deflection (FSD) linearity really mean? Is a repeatable flow meter ever any use? What about discrimination, uncertainty and rangeability?

Calibration uncertainty: How good a flowmeters calibration uncertainty is forms the basis of all the performance claims. It is a figure rarely quoted other than by certified calibration houses. No calibration, even fully traceable ones, can be absolute as there is an uncertainty on every single measurement all the way back to the National standards. Flow is a complicated product depending on a large number of variables including pressure, temperature, density, compressibility etc. Each of these measurements has an effect on the ultimate calibration result. The very best calibration houses claim an uncertainty of ±0.02% but more typical is ±0.1%. This is the base value on which all the other accuracy statements are founded. If the uncertainty quoted is ±0.2% the meter cannot be specified as being more accurate than that even if the repeatability and linearity are less than ±0.1% - the basic calibration uncertainty is the overriding number.

Repeatability: The ability of a flowmeter to give the same result on repeated runs under the same operating conditions, should not to be confused with accuracy or linearity. Without excellent repeatability a flowmeter cannot have good performance. Normally multiple points are taken at each calibration point to check the repeatability although these are not always reported on the calibration certificate. A highly repeatable meter that can be calibrated in-situ may be perfect for situations like a batching application where any offset can be reliably accounted for.

Accuracy: This term is often misused by commercial suppliers. Accuracy is the deviation from the absolute flowmeter reading, this figure should include linearity, repeatability and calibration uncertainty data. Accuracy and repeatability are not the same thing as is demonstrated in Figure 1 below.


Good accuracy & repeatability

Good repeatability / poor accuracy

Poor accuracy & repeatability

Figure 1

Linearity: The linearity of a flowmeter is the ability of the device to remain within defined limits over its entire specified flow range. The standard way of expressing linearity is “off reading” this is where the percentage error at every flow rate within the operating range is specified. An alternative linearity definition, used in some sections of the industry, is percentage of full scale deflection or FSD linearity (see Figure 2).


Figure 2: FSD linearity

The linearity of this flowmeter initially looks good as the plot of the indicated flow versus the actual flow is almost a straight line. This flowmeter is specified as ±2% of full scale accuracy so a ±2 litre per minute tolerance applies over the whole operating range, even minimum flow. If we now plot the number of pulses per litre for the same flowmeter against the flow rate (Figure 2a) a different picture of the flowmeters linearity is evident.


Figure 2a

Consequently a ±1% FSD specification can be likened to using an indicator with only 0-100 digital display. All of the readings are in 1 unit steps so at full flow you are ±1 litre per minute the same is true at 1 litre per minute which could be 0 or 2 i.e. ±1 LPM which is equivalent to 1% FSD linearity. One litre per minute accuracy at both 100 or 1 L/Min.

Obviously people do not normally claim a 100:1 flow range and a 1% FSD linearity but this a good illustration of the potential problem. Even a 10/1 flow range with 1% FSD would give a 10% permissible error at the specified minimum flow i.e. 10 LPM ±1.

By comparison if we now plot the same flowmeter data in a standard 'off reading' linearity plot (Figure 3). In this linearity performance graph the error lines are shown as percentage of reading. It is clear that the flowmeter “drops out” of the required accuracy at lower flows as the dashed line crosses the solid red lower limit line.


Figure 3:
Linearity percentage off reading

The linearity percentage off reading graphs (Figure 3 above) better illustrates the true situation. The meter is close to the maximum acceptable limit at full flow but drops outside the ±2% of reading specification at around 20 litres per minute.

Figure 4 is a typical calibration graph issued by a flowmeter manufacturer showing the permissible errors. In this case the flowmeter specification is 0 to 1 litres per minute, ±0.5% of reading. In practice this meter exceeds the specification having a linearity of +0.28% -0.1% and this includes both flow meter and calibration rig repeatability.


Figure 4

Discrimination: This term is the same as resolution. A Flowmeter’s quoted discrimination determines how small a measurement can be made. Quoted discrimination (or resolution) has nothing to do with accuracy. For instance a flowmeter which only gives 1 pulse per litre may do it between 0.999 and 1.001 Litres for every pulse 0.1% accuracy but poor discrimination.

Whereas another flowmeter may give 100 pulses per litre but only within 1% accuracy i.e. 99 to 101 pulses for each litre the discrimination is better but the accuracy is not.

Continued in column 2...

Trevor's Technical Tip -
Continued from column 2...

Rangeability: This is the ratio of minimum to maximum flow and is usually dependant on the flow meter technology used, the flow rate and the application. Some flowmeters in a production process may be required to measure flow very accurately at almost constant flow. In this case the range of the meter may only be 4:1 but the accuracy over that range could be ±0.2%. By comparison flowmeters for use on pilot plant, or as general tools in research, may require a 100:1 range but only a ±1% accuracy.


How do I measure ?

In this issue of fLowdown we discuss in 'How do I measure' an issue of general interest to many of us – fuel consumption. Don't hesitate to send your flow metering application requirements to dee@flowmeters.co.uk to see how we can help you.

The Measurement of Fuel Consumption on a Diesel Engine... Beware !

Diesel power-units are becoming increasingly popular in a whole variety of power applications. For everything from generators, boats and trains through to hydraulic packs these power sources are becoming the unit of choice. With increasing fuel prices, all sectors of the transport industries, from small trucks to large super-tankers are taking much more interest in their vehicle’s fuel consumption. The possibility of theft, particularly from remote locations makes it unwise to rely solely on a dashboard fuel gauge which simply measures the fuel left in the tank, rather than the fuel actually consumed by the engine. Despite some static installations for generators and the like lacking even a dashboard fuel gauge, engine fuel consumption and efficiency is generally not monitored and the unit’s performance is assessed from the manufacturer’s engine test figures and seldom checked again.

Whilst vehicle manufacturers do spend a lot of time and effort checking the consumption figures for an engine, this is done on dedicated dynamometers and, later, with very sophisticated mobile set ups. These fuel systems are very costly and are unsuitable for general use.

On a typical diesel engine the fuel is supplied to the injectors at pressure from a ‘lift pump’. The injectors use the amount of fuel required for the engine load and return the rest to the fuel tank. If you wish to measure the amount of fuel used you simply need to place one flowmeter in the supply line and a second in the return line and use electronics to subtract the difference: simple!

To read this article in full please click here.


New Products

Data Recording Enables Monitoring, Reporting & Management of Process Flow

Titan Enterprises has released a new data recording version of its Atrato ultrasonic flowmeter software interface. Easy to set-up and use the Atrato flow recorder enables data recording via an external computer. With features that provide monitoring, reporting and management of flow data - the Atrato flow recorder delivers a continuous picture of your process and a reliable alternative to restrictive and costly manual metering. The new software interface will be supplied with all new orders and can also be used with any Atrato flowmeter manufactured after June 2013.



Bespoke Atrato Flowmeter Systems

A long established OEM customer was having difficulties with a new chemical they were required to design their equipment to operate with. This chemical seriously attenuated the ultrasound passing through the fluid within the Atrato ultrasonic meter. The resulting, much reduced, signal amplitude proved challenging for even the Atrato flowmeter giving erroneous readings at times. The company approached Titan Enterprises to try and solve this problem with a bespoke solution.

Titan prides itself in its problem solving capabilities for organisations seeking OEM flowmeter solutions to challenging applications and set about finding a solution. After experimenting with several options the solution for the new chemical measurement was found by putting some of the setup control in their customer’s experienced hands. A bespoke version of the meters program and interface software permits the customer to alter the gain on the sensors and using the built-in bar-graph on the interface software the customer can now "increase" the gain to suit the fluid being measured. The trade off of a slightly reduced operating range and higher minimum flow was not a problem as the application did not require the 200:1 turndown that Atrato normally provides.

Over recent years this customer has systematically been replacing oval gear flowmeters in different applications with the highly reliable Atrato ultrasonic flowmeter. The customer likes that the Atrato has no moving parts and a through bore construction is seen as a big benefit as both service and downtimes associated with the metering system is all but eliminated. The more flexible output from the meter is also seen as a bonus as requirement for secondary instrumentation is reduced.

Flow Technology Spotlight

In each issue of fLowdown we will review a particular flow metering technique, its benefits, shortfalls and the applications to which it is best suited. In this issue we look at the turbine flowmeter.

Turbine Flow Meters

These devices were historically the flowmeter of choice for clean, filtered, low viscosity fluids. Their design and working principles are well understood, they have a relatively low pressure drop for in-line meters and can give excellent accuracy. They are used for both lower viscosity liquids and gases with turn down ratios from 7 to 30:1. This extended range is achieved by using a suitable zero drag electronic pick off instead of the standard magnetic type which causes too much extra drag to the turbine at low fluid velocities slowing the rotational speed. Accuracies of ±0.25% and repeatability of better than ±0.05% are achievable although more typically ±0.5% accuracy and ±0.1% repeatability. The larger the meter the more accurate it is likely to be as designing "miniature" axial turbines is plagued by a large number of potential problems. They are inherently Reynolds number sensitive and will not be linear at Reynolds numbers approaching or in the laminar region. For this reason care must be taken when using these meters with fluids that have a wide viscosity/temperature range for example some oils. At constant conditions there is no problem but in practice this is often difficult to achieve.

Meter design.

In principle designing an axial turbine is easy, put a propeller in a tube. In practice years of experience have developed the basic design to a quite complex assembly. Keeping the turbine spinning freely is the main object of any design so particular attention is made to bearing design and sources of drag within the assembly. This is one of the reasons that miniature axial turbines are difficult to make as the relative turbine energy is largely cancelled out by the bearing and sensor drags. Either plain bushes or roller/ball bearings are used for the rotational efficiency and usually a ball is used to take the end thrust. Some designs have hydrodynamically designed turbine and bearing supports which create a low pressure area in front of the turbine which "pulls" it forward so reducing or eliminating the end thrust. The bearing supports are designed to reduce the pressure drop whilst increasing the fluid velocity over the turbine blades. As mentioned previously the sensor is usually magnetic giving a low voltage sine wave output. When extra accuracy, extended flow range or the meter is operating in an electrically noisy environment an electronic pick-up is often used. There are modern miniature variants where the turbine has plain blades in-line with the flow and the actual fluid is rotated by the upstream bearing support which is twisted to swirl the flow onto the plain blades. I have also worked on the original design for a double ended bearing less turbine where the axle was fully supported by the fluid with no turbine contact with the body or bearing drag. A 40 year old prototype turbine assembly is currently used as a paper weight on my desk (see image below). This meter was developed to be an all polymer meter for very aggressive chemicals.

Advantages of turbine flowmeters

♦ Simple well understood technology.

♦ Low cost.

♦ Relatively wide operational envelope.

♦ Easy to install and operate.

♦ Good performance.

♦ Suitable for gases and liquids.

Disadvantages of turbine flowmeters

♦ Fluids must be clean.

♦ Require careful installation to avoid
   errors.

♦ Cavitations cause problems.

♦ Require frequent calibration checks.

♦ Bearing degradation affecting
   accuracy.

♦ Viscosity changes cause errors.

Applications for turbine flowmeters are found in monitoring clean liquid flows in the water, petroleum, and chemical industries. Water applications include distribution systems within and between water districts. Petroleum applications include the custody transfer of hydrocarbons. Miscellaneous applications are found in the food and beverage, and chemical industries.

For further information on turbine meters from Titan Enterprises please click here.


Humour

Some humorous asides for the Engineers amongst us:


A jumper cable walked into a bar. The bartender said, "I'll serve you, but don't try to start anything."


I'm reading a book about anti-gravity. I just can't put it down.


There is a new band called 1023MB. Unfortunately they haven't had any gigs yet.


A photon checks into a hotel and the bellhop asks him if he has any luggage. The photon replies "No I'm traveling light."


Bulletin Board

To enable you to make informed decisions about the flow metering challenges facing your organisation this regular newsletter feature keeps you up-to-date on the latest literature, web, video and social media initiatives from Titan Enterprises.

Oval Gear Flowmeter Selection Chart

For many years - Titan Enterprises has invested in development of its range of high performance oval gear flowmeters. To view a selection chart to help you select the optimum oval gear flowmeter for your application please visit www.flowmeters.co.uk/oval_gear_meters.htm.



Technical Article:
Metering Petrochemical Additive Injection Fluids

For the successful transportation and refining of crude oils a whole raft of additives are required. These vary from simple surfactants through to complex blended scale and corrosion inhibitors. These chemicals are injected in small quantities at high pressure and are critical to the whole refining process. Consequently careful monitoring of their addition to any process is essential, often this is best done using a flowmeter. Petrochemical additive injection fluids vary in viscosity and density and any flowmeter installed into a plant should be able to cope with a wide range of physical and chemical properties. The choice of flow measurement solutions is still quite narrow with only a few technologies offering acceptable measurement resolution.

Titan Enterprises has written a new article that reviews currently used flowmeter technologies for metering petrochemical additive injection fluids and looks ahead to new advances on the development horizon. To request a copy of this article please click here.



Technical Article: Flow Measurement in the Laboratory

Flow measurement in a typical laboratory or pilot plant poses unusual problem. Inevitably the pipes are small and the flow rates low and these factors introduce some unique problems.  The low energy available from the fluid,  the miniaturisation of flowmeter components and fluidic considerations are discussed in a new technical article written by Titan Enterprises. To request a copy of this article please click here.





Titan Enterprises Reports Growth in Flow Meter Exports

Titan Enterprises has reported a doubling of the number of flow meters sold to export markets during its last financial year. During the year – Titan saw record production of over 45,000 flow meters shipped to 34 countries worldwide. Notable growth was seen in sales of the company’s innovative Atrato ultrasonic flow meter as well as its popular Oval Gear (OG) and 1000 Series flow meter ranges. With flow measurement solutions being supplied to a broad range of market sectors including medical, chemical, petrochemical, food and drink, laboratory and pharmaceutical – Titan Enterprises reported biggest growth in demand from China, Denmark, Ireland, Singapore and the USA.

Click here for a printable version of Flowdown.

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Titan Enterprises Ltd, Unit 2, 5A Cold Harbour Business Park, Sherborne, Dorset, DT9 4JW. UK
Telephone: +44 (0)1935 812790 - Fax: +44 (0)1935 812890 - Email: sales@flowmeters.co.uk