Survey on the Techniques of Flow Measurement

Transcription

1 Survey on the Techniques of Flow Measurement by Group C Aiman Haikal Bin Zaharudin (AD150193) Muhammad Amir Aiman Bin Desa (AD150284) Izrul Azraei Bin Ibrahim (AD150008) Muhammad Riduwan Bin Husin (AD150097) Muhammad Amin Bin Ali (AD150221) A report submitted in partial fulfilment of the requirements for the course of Control Engineering (BDA30703) Faculty of Mechanical and Manufacturing Engineering Universiti Tun Hussein Onn Malaysia Semester 1, 2017/18 Assessment for the assignment (Rank: 1(very poor) to 5(excellence)) Sections Weight Rank Marks = weight x rank Remarks Introduction 5 Techniques 5 Discussion 5 Conclusion 3 Reference 2 Total 20 /100

2 1.0 INTRODUCTION A basic instrumentation system consists of various devices. One of these various devices is a transducer. A transducer plays a very important role in any instrumentation system. An electrical transducer is a device which is capable of converting the physical quantity into a proportional electrical quantity such as voltage or electric current. Hence it converts any quantity to be measured into usable electrical signal. This physical quantity which is to be measured can be pressure, level, temperature and displacement. Flow measurement is a method of measuring how much of a material flows through a particular area of interest. Generally, industrial processes demand for the measurement of three types of materials which are solids, liquids and gases. Solids are usually measured on their weight, liquids can be either measured in terms of their weight or volume and gases are usually measured in terms of their volume. Figure 1 show the typical flow measurement set-up. 1.1 The importance and significance of flow measurement. Flow measurement is accomplished through the use of flow meters. The flow meter is a type of device that is used to measure the amount of liquid or gas that moves through a pipe. This is commonly referred to as the flow rate. The applications of flow measurement are diverse and every situation features its own engineering requirements and limitations. Depending on the industry, various terms are used to refer to a flow meter and they range from flow gauges to liquid meters.

3 Regardless of the names that are used for this particular device, the function is always the same which is measuring flow. A flow meter serves the purpose of providing accurate monitoring or flow control. The need for precise calculations of quantities or measurement accuracy will vary with different industrial applications. Flow sensors are the devices which are used to monitor the change in a particular parameter. Accordingly, flow sensors are the devices which are used to monitor the changes in the flow rate of a particular state of matter. These are expected to record even the slightest changes in the flow rate and high precision. Existence of numerous kinds of flow meters and flow sensors are a direct consequence of the importance which is attributed to the concept of flow measurement in numerous industrial applications including the design of automatic control system. 2.0 Objectives 1. To know the basic theory of flow measurement of transducers. 2. To determine the different techniques used in flow measurement which is flow transducers to measure air flow velocity with different measurement ranges, flow transducer to control flow rate and transducers to determine flow velocity and volume. 3. To find the advantages and disadvantages of the techniques in particular with respect to the performance and costs.

4 3.0 Example of Flow Measurement Transducers 3.1 Transducer to determine volume and flow velocity Flow meter (cross meter) models X8 and X16 are used to determine the volumetric flow and the velocity flow. The total pressure is determined and calculated by periodically spaced holes which are in a diagonal line. The ratio of the dynamic pressure is calculated by subtracting the sub static pressure. This is determined by the second tube and it is always less than the static pressure in the system. Due to the minimal loss of load, the measurement signal doubles. Figure 1: View Of The Flow Meter Series Figure 2: Working Principles Of The Technique The pressure signal is sent to the meter to determine the pressure, the flow velocity or volume. By using a pressure gauge with an analogue output (with or without display) the flow meter becomes a complete and economic package for measurement and flow regulation. The flow meters are simple pressure sensors. To assess the signal a proper meter is needed. The choice of meter depends on the type of measurement, as shown in the picture above The Device Description Basically, the flow meter X8 and X16 models are designed as basic pressure sensors for rectangular air ducts. These flow meters are simple and inexpensive and it is an accurate alternative to other pressure measurement systems. This type of flow meter is delivered as a construction set and is suitable for all pipes with a maximum diagonal of 1400 mm (model X16) or 700 mm (model X8). The maximum diagonals for ideal ducts are 700 mm and 1400 mm respectively, which means the sensors, are suitable and available in wide range of piping installation. Apart from that, the sensors also can achieve a maximum 80 ºC of operating temperature which make it more durable and a good high temperature resist. The velocity range that the sensors can manage to detect is around 5-30 m/s with an accuracy of < ± 5 %. It is such a big favorable sensor in a certain field as it only required a simple construction, easy installation and low in maintenance.

5 3.1.2 The device application in engineering Usually, the sensors have been widely used in ventilation, air conditioning, medium piping installation etc. With their universal size, cross grids are not only ideal for expanding existing facilities but can upgrade them significantly. The uses of the sensors are especially useful for places where more expensive methods of measurement, such as Wilson grids, are not suitable or where accuracy is not the primary goal. 3.2Flow Transducer to Control Flow Rates Working Principle 1.The gas, which enters from the inlet, first splits to flow past the sensor or through the bypass. 2.At the sensor, the mass flow rate is detected as a proportional change in temperature and converted by the bridge circuits to an electrical signal. 3.This signal passes through the amplification and correction circuits, and is output as a linear voltage between 0 to 5V. At the same time, it is also sent to the comparison control circuits. 4.The comparison control circuit compares the flow rate setting signal and the acutual flow setting signal from the sensor and sends a difference signal to the valve driving circuit. 5.The flow rate control valve movers as appropriate to make the difference between the reguired flow set point and flow output signals approach zero. In other words, the unit controls the flow so that it is always at the set flow rate.

6 3.2.3 Description Flow tranducer to control flow rate is basically works by measuring the mass flow rate as the basis of most formulations, material balance determinations, and billing and custody transfer operations throughout industries that need to measure flow. With these being the most critical flow measurements in a processing plant, the reliability and accuracy of mass flow detection is very important. Mass flow also can be measured by batch weighing or by combining an accurate level sensor with a densitometer. Another method is to mount two d/p transmitters on the lower part of an atmospheric tank at different elevations. In this case, the output of the top d/p cell will vary with the level in the tank, while the lower one will measure the hydrostatic head over a fixed elevational distance. This pressure differential yields the density of the material in the tank. Such systems have been used to measure the total mass flow of slurries. This is how measurement of the Coriolis force exerted by the flowing fluid on the rotating tube can provide an indication of mass flowrate. Naturally, rotating a tube is not practical when building a commercial flow meter, but oscillating or vibrating the tube can achieve the same effect. Coriolis flow meters can measure flow through the tube in either the forward or reverse directions. This resonant frequency is selected because the smallest driving force is needed to keep the filled tube in constant vibration Application 1. Pumping Station Widely use in pumping station to determine the change in flow rate of water during pumping out water from water pumping station to the reservoir. The sensor has been installed on a stainless steel plate to prevent the sensor from obstruction and to avoid vorticity on the channel bottom.

7 2. Hydroelectric Reservoir Applied in turbine meter and multi bladed rotor to ensure the rotation of the turbine is propotional to the velocity of fluid. Turbine flowmeters use the mechanical energy of the fluid to rotate a pinwheel (rotor) in the flow stream. Blades on the rotor are angled to transform energy from the flow stream into rotational energy. 3. Piping Area For the piping, its direction it s avoid downward flow in liquid applications size, material, schedule, flange-pressure rating, accessibility, up or downstream turns, valves, regulators, and available straight-pipe run lengths Flow Transducers to measure air flow velocity Flow transducers are used to measure air and liquid flow velocity. Flow transducers use different measuring principles Flow transducers to measure air or liquid flow velocity. By means of the flow velocity, analysis units of flow transducers can calculate the flow level or determine the amount of flow with a counter. Air flow transducers are mainly used in the heating, ventilation and conditioning sectors. Flow transducers use the manometric method which allows the usage for a wide range of temperature and flow. Simple method of measuring air velocity by using flow meter transducers Working Principle The way to acquire the average flow rate measurement across differing cross-sections of duct. The physics are relatively simple: 1. Air is slowed by friction with contact to the edge of the duct 2. The greatest air velocity is achieved under laminar flow conditions in the frictionless middle of the cross-section

8 3. The velocity profile of the duct is dependent on the shape of the duct (minimizing perimeter walls to achieve cross-sectional area) and the force pushing the air. Data collection, accurately and precisely measuring air velocity across ducts, has been a difficult task. And, poor data collection procedures produce the errors in duct balancing. The newest microprocessor-based instruments complete duct hvac air flow measurement data collection accurately even before the patience of the HVAC tech wears out. Example of working principle in differential pressure type in flow measurement Application 1. Tunnel Ventilation System Airflow measurement systems are specifically designed for working under conditions prevailing in road tunnels. In the driving area there are only robust mechanical sensors made of stainless steel, the evaluation electronics is located in a separate control room. The high-resolution measurement allows continuous blower control and thus an effective optimization of fans and power consumption. Measurement is based on highprecision differential pressure measurement (Pitot tubes) which results in accurate flow measurement of the air through the tunnel. The data from the separately mounted field transmitters are transferred digitally into the evaluation unit.

9 4.0 Discussion: The Advantage and Disadvantage of Flow Measurement Transducer In order to get a best measurement device for a best measurement solution, the advantages and disadvantages of the device ought to be considered. Flow measurement transducer is used to measure air and liquid flow velocity. Flow measurement transducer uses different measuring principles. In general, the advantage of flow measurement transducer is that it is relatively inexpensive. Wasn t it is a good thing? When it s inexpensive, definitely we can save the cost hence avoiding us from wasting too much of our money. Moreover, it is a simple technology with no moving part. Transducer is the primary device of flow meter. The fluid that passes through the primary device is sensed by the transducer. Besides, air flow transducers are mainly used in the heating, ventilation and conditioning sectors. The other advantage of flow measurement transducer is that it is usable over a very wide range of size hence we can choose and use from different range of size. Within that, it is a compact sensor which make it ideal for use especially in the industrial applications and it offers great flexibility in installation. Furthermore, the advantage is that it is configurable for bi-directional flow hence make it easier to obtain the result. When there is advantage of this transduser, there must be the disadvantage of the device. Hence, the disadvantage of the flow measurement transducer is that it has a limited accuracy. The reading obtained should be taken more in order to increase the accuracy. It means that it must not only depend on one reading obtained, hence repeat again to get an accurate reading. Next, it can causes a pressure drop and reduces pipe s free passage thus make it harder to get a best solution. Besides, it depends on good pressure sensor practice. It cannot be used in a rough way because it can cause a damage to the pressure sensor. The other disadvantage is that the changes in liquid characteristics can affect the readings obtained. Moreover, for orifice meter, it requires straight pipe runs to ensure accuracy is maintained and pipe line must be fully especially for liquid flow measurement.

10 5.0 CONCLUSION As for conclusion, we already know the basic theory of flow measurement of transducers. Flow measurement is often an important parameter in several processes. It is associated with asset management, tank balancing and maintaining fluid motion. Some applications need the ability to carry out accurate measurements because of their extensive influence on product quality, safety, health and overall profitability. In some cases, inaccurate flow measurements or failing to take these types of measurements can result in drastic consequences. With the variety of gas and liquid flow measurement devices, it can be difficult for operators to decide which technology will be suitable for the application. The different techniques used in flow measurement have been determined which is flow transducers to measure air flow velocity with different measurement ranges, flow transducer to control flow rate and transducers to determine flow velocity and volume. 6.0 References 1. ENGINEERING, O. (n.d.). FLOW METER INTRODUCTION TO FLOW MEASUREMENT. Retrieved SEPTEMBER 24, 2017, from 2. IInst., P. (n.d.). FLOW METER (CROSS METER) X8 / X16. Retrieved SEPTEMBER 24, 2017, from