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Incontrol publication intended to narrate cases in flow and level measurement

Responsible Journalist: Gildo Mazza (MT 17830)

In-line or insertion electromagnetic flowmeter. Which one to use?

What is the difference between in-line magnetic flow meter and insertion magnetic flow meter?

When can we opt for in-line and when for insertion?

These questions are very common: which is the most efficient and reliable, which is the most practical and economical. This article is precisely to clarify the efficient and economical option. Let's talk about the differences covering application, precision, installation and investment cost of each one. We are sure that at the end of this reading you will have answers to the questions above.
First, it is good to remember that most flow meters, regardless of the operating principle, are velocimetric meters, that is, they measure the flow speed.
Flow meters must always be installed in full (flooded) pipes, with upward flow and without air bubbles.

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The principle of electromagnetic flowmeter is based on Faraday's law of induction. The applications of this law are countless and we can mention: inductors, alternators, dynamos and transformers. But let's stick to our topic: flow meters.

In-line meter
The conventional, in-line flow meter is mounted on a non-magnetic tube, where two coils are fixed, one at the top and the other at the bottom. When energized, they form a magnetic field surrounding the entire area of the tube. When flowing through the pipe, the conductive liquid crosses this magnetic field, generating an e.m.f. (electromotive force) proportional to the speed of its flow. In other words, the higher the flow speed, the higher the e.m.f.; the lower the flow velocity, the lower the e.m.f. (This is why some meters don't measure low flows well). The electrodes are installed on the sides, fixed and centered with micrometric precision (the electrodes and their perfect fixation are the heart of the meter). These capture the e.m.f. and send it to the secondary, also known as the flow converter. Upon receiving the e.m.f. proportional to the “speed” of the measured liquid, its processor, through dedicated software, performs the functions and calculations, converting the information into flow indication.

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Such an explanation is necessary to understand that the physical construction of the in-line flow meter is reliable and the equipment can be used for both measurements continuous as in “batches”, in a wide range of applications, such as: milk, soft drinks, acids, raw and treated water, or dirty and pasty, such as kaolin, sewage, mud, curd, etc. It has good accuracy even with liquids with low “conductivity” (≥ 5 μs) or low flow rates. It is capable of operating at speeds of 0.1 m/sto 0.3 m/s with an accuracy of better than 2% (for monitoring and controlling leaks in night flows by water companies) and from 0.3 m/s to 10 m/s with an accuracy of 0.5%. It has good performance in conveying between collection, treatment, reservation and distribution. Operators of sanitation companies perform various maneuvers in the networks, such as opening and closing valves and turning on or off pumps, among other actions, which end up constantly changing the flow and the profile of the speed curve. The in-line meter can measure with minimumerror even with these sudden and constant variations.


“Therefore, we conclude that the line electromagnetic flow meter is very reliable and accurate, and can be installed in any process.”

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Insertion meter

The insertion flow meter, although with the same principle, is physically assembled completely inversely to the in-line flow meter, that is, a single coil is fixed inside a non-magnetic rod, which when energized forms a magnetic field around it. . By alternating the polarity of the coil, the field also alternates, time from bottom to top, time from top to bottom. The magnetic field is generated from the inside to the outside of the rod. With the passage of the “conductive” fluid, the e.m.f. is generated. captured by the electrodes also fitted one on each side of the rod and positioned micrometrically in the middle of the magnetic field (much better than other models, which holds the electrodes at the tip of the rod). The rod can be inserted into pipes of any diameter, whether small, such as 200 mm, or large pipes, 2,000 or 3,000 mm. The e.m.f. is sent to the secondary, which is the same as the in-line meter and with the same functions and calculations for indicating the flow, simply programming the ∅ of the pipe. Such an explanation is necessary to understand that the physical construction of the insertion magnetic flow meter has its limitations, as it measures punctually, that is, only at one point on the speed curve. That's why your error is a little bigger, especially if there are constant changes in this curve. It is only used for continuous measurements in liquids with few suspended solids, raw water and treated water, with conductivity above 50 μs.

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Comparação financeira

Os macromedidores de vazão eletromagnéticos in-line são instalados nas adutoras da forma convencional. Corte na adutora, instalação de junta de expansão para ajuste entre adutora e medidor, solda de flanges nas duas extremidades, encaixe do macromedidor entre elas e fixação por meio de parafusos e porcas. Devem ser instaladas ainda, entre flanges, juntas de vedação para evitar vazamentos e anéis de aterramento, pois sem isso o medidor não funcionará corretamente. Este processo de instalação é demorado e caro, além de necessitar de profissionais especializados em caldeiraria e em solda no local. Construtoras especializadas em instalação de macromedidores de vazão tem um cálculo prático do custo da instalação de um macro, que geralmente é de 2 a 3 vezes o valor pago pelo equipamento, dependendo do local onde instalado. Sob ruas ou avenidas com trânsito pesado, alcança até 4 vezes, considerando também a confecção da caixa. Portanto para um rápido cálculo de custo da instalação de um macro de 400 mm com um custo básico de R$ 13 mil, podemos considerar mais R$ 39 mil para ter este medidor instalado e funcionando.

Além do custo é imprescindível o planejamento para a instalação pois isso poderá gerar consequências causadas pela paralisação do abastecimento quando da instalação do medidor. Os macromedidores de vazão eletromagnéticos de inserção não necessitam de profissionais especializados, soldas ou acessórios para sua instalação. Um simples “tap” de pitometria, que geralmente já está instalado na linha, é o suficiente. Pode ser inserido e sacado com a adutora em plena carga. Outra vantagem é o mesmo medidor poder ser instalado em qualquer diâmetro, seja de ∅ 100 mm, ∅ 500 mm ou ∅ 1.500 mm em tubos de qualquer material.

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In places where there is no measurement at all or cities with little funding to start control of losses between collection, treatment and distribution, the insertion magnetic meter is the ideal solution as long as it has a good straight section upstream and downstream to improve the speed profile. “The advantage of the insertion magnetic flowmeter is not only in the acquisition cost; more than that, it’s in the installation cost.” Some municipal sanitation companies and even private utilities, in the desire to create their control and loss management often specify flanged, in-line magnetic flow meters. This is correct, but in certain cases, in diameters above 250 mm, an insertion gauge could be specified in order to reduce costs and increase the number of gauges. Let's look at some cases where both options were under discussion.

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Case 1

We recently visited a city on the banks of the Amazon River that captures 1,360 L/s. With funding from the PAC, plans were initiated to monitor the collection, treatment and distribution of water in the most important points. After surveying the costs of equipment and installations, they concluded that they could purchase only 14 meters, including the main one, in the collection on the Amazon River, in a 1,000 mm pipe. As the responsible engineer is very interested in new flow measurement concepts, he asked us to present these new features. We showed the advantages, the cost reduction and installed for a period of 60 days on a consignment basis an electromagnetic meter for insertion precisely in the catchment area of the Amazon River, where the water is quite turbid. One day after start up, the engineer asked us to remove the sensor from the pipe, as after more than 24 hours indicating, transmitting and totaling the flow he believed that algae and mud pumped with the water would be a serious aggravating factor for the measurement. When we took out the sensor, we were surprised by the accumulation of “snot” embedded in the sensor and it was indicating correctly. At your request, we clean the sensor and reinsert it into the measurement location. The engineer suspended the purchase of the 14 planned flow meters and today has plans to acquire 38 magnetic meters, the vast majority of which will be inserted by Incontrol and installing them for the same price would allow you to purchase “only” the 14, such was the savings you saw. According to the responsible engineer, what impressed him more was the ease and time it took us (3 hours) to install, pull the wires, connect and receive the signal on the computer in your room. Seeking to minimize costs, in locations with a good straight section and a defined velocity profile, we recommend opting for insertion flow meters for pipes with ∅ greater than 250 mm.The value of the flow meter per insertion for any pipe diameter is R$ 13,800.00 including taxes, surge protectors, interconnection cable, packaging and shipping included. The cost of installing the VMI flow meter per insertion, excluding the box with “TAP” (PV), is zero as any Pitometria employee can easily insert it into the line and the parameterization can be based on Pitot information.

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Case 2

A long time ago we were in Ceará, where we met an engineer who was unhappy with a magnetic flow meter for collecting raw water measuring ∅ 1,500 mm. There had been problems and the technicians from the company supplying the equipment told him that he should send it to São Paulo. He, in the urgency of continuing the measurement, immediately tried to request the meter to be removed from the line, they manufactured a “stub”, and after authorization from several departments, they began emptying the pipeline (it took hours), calling a team of six men to loosen the screw nuts, lift the ± 1,500 kg macro with a crane, place the stump, retighten, eliminate leaks, restart pumps and fill the pipes. On our way through the city, without knowing what had happened, we went to visit him to show him the news. Then he discovered that he could have left that macrometer in place like a stump and installed the Incontrol magnetic insertion meter on the pitometry “tap” existing a few meters from the meter, without stopping pumping and emptying the pipeline, at a lower cost than the rental value of the crane used. He immediately went down to the box where the “stump” was now and pointing and saying: “I want the Incontrol magnetic insertion flow meter in this place and I'm not even going to get the macro back, as the repair was even more than the price of this formidable option.” The moment was immortalized on our cell phone, as can be seen in the photo to the side.

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Case 3

In this case we will only show the internal newspaper (authorized by the client), which says much more than we could tell.

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