Ultrasonic flowmeter is an instrument that measures liquid or gas flow through ultrasonic technology. It works on the basis that the speed at which sound waves travel through a fluid changes depending on the direction and speed of the fluid flow. Ultrasonic flowmeter is widely used in industry, petrochemical, water supply system and environmental engineering and other fields.
Working principle
Ultrasonic flowmeters usually use the following two main working principles:
1. Time difference method (also known as propagation time method) : This method relies on the time difference of ultrasonic signal propagation in the fluid to measure the flow rate. Assume that there are two pairs of ultrasonic sensors, installed in the upstream and downstream positions of the pipeline, forming a symmetrical measurement path. Ultrasonic signals travel at different times in both upstream and downstream directions:
a.Downstream direction: The ultrasonic signal travels in the direction of the fluid flow, and its propagation speed will be accelerated.
b.Countercurrent direction: The ultrasonic signal travels against the direction of the fluid flow, and its propagation speed will be slowed down.
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By measuring the travel time in these two directions, the flow rate of the fluid can be calculated. The difference in travel time is proportional to the velocity of the fluid.
Advantages:
• High accuracy: Especially suitable for single, clean liquids, the best results when the fluid does not contain impurities or bubbles.
• Wide application: Suitable for measuring various pipe diameters.
Cons:
• Depends on the acoustic properties of the fluid: it is greatly affected by impurities or bubbles in the fluid.
• Accuracy degrades in the case of fluid turbulence or uneven flow velocity distribution.
2. Doppler effect method: This method uses Doppler effect to measure flow. The Doppler effect method uses changes in the frequency of sound waves to measure velocity. Reflections occur when ultrasonic waves travel through the fluid and meet suspended particles or bubbles. If the fluid is in motion, the reflected ultrasonic frequency will be different from the emitted frequency, and this change in frequency is the Doppler effect.
• When the fluid moves towards the sensor, the frequency of the reflected wave increases.
• When the fluid moves away from the sensor, the frequency of the reflected wave is reduced.
By measuring the difference in frequency between the transmitted and received waves, the flow rate v can be calculated.
Advantages:
• Ideal for measuring fluids containing suspended particles or bubbles: not limited by fluid purity.
• Wide range of application: can be used to measure dirty liquid or high bubble content of fluids.
Cons:
• Dependent on scattered particles or bubbles in the fluid: Sufficient reflective particles are required in the fluid to make measurements.
• Low relative accuracy: The measurement results are more sensitive to noise and flow conditions.
Channel concept
In ultrasonic flowmeters, channels refer to the number of paths through which ultrasonic signals propagate. Each channel consists of a pair of transmit and receive sensors that measure flow. The use of multiple channels can improve the accuracy and stability of measurement. Common channel configurations include single-channel, dual-channel, and four-channel configurations.
Single channel (1 channel) : The flowmeter uses only a pair of sensors to form a measurement path. It has the advantages of low cost, simple installation, but relatively low measurement accuracy, especially in the case of uneven fluid flow distribution.
Dual channel (2-channel) : two pairs of sensors are used to form two measurement paths. The two-channel configuration significantly improves measurement accuracy because it allows the flow rate of the fluid to be sampled at different locations, reducing the impact of uneven flow distribution on measurement results.
• Four channels (4 channels) : Four pairs of sensors are used to form four measurement paths. This configuration provides higher measurement accuracy and stability for applications that require high precision measurements, such as large pipelines or environments with complex measurement conditions. The four-channel configuration can more fully reflect the flow velocity distribution of the fluid and reduce errors.
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In the field of chemical engineering, there is a requirement that the length of the bolt should not be too long or too short, and the flange bolt should be left with 2 to 3 wires. For this part of the requirements, this public number has a simple introduction, see: Basic knowledge - Why should the bolt leave 2-3 wires
So how to determine the length of the bolt supporting the flange?
First of all, we definitely need to determine the thickness of the flange.
We can inquire the corresponding thickness of different types of flanges by referring to various standards. Here you can refer to GB/T 9124.1-2019 "Steel pipe flange: PN series". From this standard, we can obtain different types, different sealing surfaces, different nominal diameters and different nominal pressures under the thickness of the flange.
Secondly, we need to determine the thickness of the gasket between the flanges.
This in turn involves a series of standards, such as: GB/T 4622.1-2022 "Winding gaskets for pipe flanges Part 1: PN series" and so on. Of course, although the gasket has thickness requirements, its thickness will be reduced in the fastening state. Moreover, under normal circumstances, the thickness of the gasket is about 4 mm, so in order to quickly calculate the length of the flange supporting bolts, we can directly set the thickness of the gasket to 4 mm or 5 mm.
Then, you need to determine the length of the nut to be matched with the bolt.
This still needs to query the standard to obtain the required nut length, usually the standard to query for these two standards: GB/T 6170-2015 "Type 1 hex nut" GB/T 6175-2016 "Type 2 hex nut".
We can see that the nut length of a type 1 nut is about 0.8 times its large diameter. The length of a type 2 nut is approximately 1 times its large diameter. Therefore, we can quickly determine the length of the nut by the screw thread type of the nut, usually we choose 1 times the size of the nut.
In addition, we also need to determine the length of the reserved bolt.
Since our bolt needs to leave 2 to 3 wires after fastening the nut, it is necessary to determine the corresponding length of these 2 to 3 wires. We also need to query the corresponding standards, such as: GB/T 196-2003 "Basic dimensions of ordinary threads". From the standard, we can obtain the corresponding pitch of different types of threads, so as to calculate the length required for 2 to 3 threads.
Finally, we also need to determine the number of bolts and thread specifications corresponding to a flange. These two data can also be obtained from the standard GB/T 9124.1-2019 "Steel pipe Flanges: PN Series". The standard lists different flange types, nominal pressures, the number of bolts corresponding to nominal diameters, and bolt thread specifications.
After the above steps, we can calculate the length of the bolt required, the length of the bolt includes: the thickness of two threads, the thickness of the sealing gasket, the thickness of the two nuts, and the height of the reserved 4~6 threads.
The above calculation process is very complex and requires querying a large number of criteria. Moreover, the calculation process is complicated and time-consuming.
How to solve it? Coincidentally, in order to solve the query and calculation problems of flange matching bolts, this public update adds the query and calculation function of the number and length of flange matching bolts.
The new function is located in the flange model screen. By selecting the flange type, you can quickly query the number and length of bolts supported by the flange.
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Coriolis mass flowmeter is based on the Coriolis principle, so that the medium flows through the flow tube vibration, the sensor detects and analyzes the flow tube frequency, phase difference and amplitude changes, directly measure the current flow of the flow tube media quality, from the vibration frequency, calculate the density. Multiple process variables of the pipeline can be measured at the same time, such as: mass flow, volume flow, density, temperature.
Coriolis Flow meter VS Thermal Flow meter:
Coriolis flowmeters measure mass flow directly. Direct mass flow measurement reduces inaccuracies caused by fluid physical properties. Thermal flowmeters measure mass flow indirectly. There are fundamental differences between the two devices because of the way they are measured, and therefore the applications for which they are suitable are also different.
Thermal mass flowmeters use the heat capacity of a fluid to measure mass flow. The device is equipped with a heater and 1 or 2 temperature sensors for heating (1 sensor) the applied power or temperature difference between the 2 sensors is directly proportional to the fluid mass flow rate. Thermal mass flowmeters are mainly used for gases.
Because the Corrioli principle directly measures the mass flow rate, Corrioli flowmeters can be used for gases and liquids.
Applications:
Coriolis mass flowmeters can be used to measure the mass flow of changing or unknown gas or liquid mixtures or to measure supercritical gases. It not only directly measures the mass flow rate, but also has high accuracy and good repeatability. Coriolis flow meters are flexible, reliable and accurate flow meters.
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✦Principle
The metal tube float flowmeter has the advantages of simple structure, reliable operation, high accuracy and wide application range. It can withstand higher pressures than glass rotameters. NYLZ-L series flowmeters have local indication, electrical remote transmission, limit switch alarm, corrosion resistance, jacket type, damping type and explosion-proof varieties. Widely used in national defense, chemical, petroleum, metallurgy, electric power, environmental protection, medicine and light industry and other departments of liquid, gas flow measurement and automatic control.
When the bottom-up fluid passes through the upright measuring tube, the float rises under the action of the pressure difference, and the height of the float rise represents the size of the flow. The magnetic steel in the float is coupled with the magnetic steel in the indicator and transferred to the indicator to drive the pointer in the indicator to rotate.
✦Show fault phenomenon
Valve fully closed, flowmeter indicates full scale
✦Process check
1, the valve is fully closed, the flow meter indicates full scale, first consider the flow meter rotor stuck.
2, whether the rotameter head is damaged, whether the cone tube is blocked.
✦Treatment method
1. Use a screwdriver to absorb the magnetic part of the rotameter to initially check the reaction of the flowmeter, normal, no falling off phenomenon, tap the bottom of the flowmeter with a rubber hammer, and still show the full scale, and judge it as the rotameter card.
2. Remove the thermal insulation cotton, open the heat tracing, wear gloves, and prepare to remove the flow meter.
3, remove the four screws of the lower flange, the force should be uniform, and then remove the screws after the pressure is discharged.
4, remove the flow meter, remove the circlip, remove the rotor, the rotor is attached with iron powder. Wipe off with a rag and rinse with water.
5. Install the rotor, move up and down with the screwdriver against the rotor, move flexibly, and install the flowmeter.
6, the flow meter to the process use, normal operation.
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Pressure transmitters are one of the most common sensor types used in industrial automation control. Piezoresistive type, capacitive type and monocrystalline silicon resonant type are three main types, each with its own unique working principle, advantages and disadvantages and application scenarios
Piezoresistive pressure transmitter
Working principle
Piezoresistive pressure transmitters use the piezoresistive effect of monocrystalline or polysilicon to convert mechanical deformation caused by pressure into electrical signals:
1. The pressure acts on the sensing diaphragm, and the diaphragm becomes elastic deformation.
2. The piezoresistive element (resistor) on the diaphragm changes its resistance value due to force.
3. The resistance change is converted into a voltage signal through the Wheatstone bridge, and the output electrical signal is proportional to the pressure.
Advantages:
1. High precision.
2. Simple structure and low cost.
3. Fast response speed, suitable for dynamic pressure measurement.
Disadvantages:
1. It is sensitive to temperature and needs temperature compensation.
2. Susceptible to mechanical vibration.
3. General long-term stability, large drift.
Application scenario
• Pressure measurement of liquids, gases and vapors.
• Extensive engineering applications, such as water treatment equipment, automotive oil pressure, refrigeration systems, etc.
Capacitive pressure transmitter
Working principle
Capacitive pressure transmitter uses pressure to cause capacitance change principle:
1. The pressure acts on the metal or non-metal diaphragm, causing elastic deformation of the diaphragm.
2. The diaphragm and the fixed electrode form a variable capacitor, and the pressure change causes the capacitance value to change.
3. The capacitance change is converted into an electrical signal, and the output signal is proportional to the pressure.
Advantages:
1. High sensitivity, especially suitable for small pressure measurement.
2. Low temperature effect, good long-term stability.
3. Suitable for high and low pressure measurement.
Disadvantages:
1. Sensitive to impurities, moisture and other environments, requiring special treatment.
2. The signal processing is complex and the cost is relatively high.
3. The response speed is slightly slower than piezoresistive type.
Application scenario
• Precision scenarios, such as medical air pressure, food processing equipment.
• High temperature, high pressure, highly corrosive conditions, such as chemical and petroleum industries.
Monocrystalline silicon resonant pressure transmitter
Working principle
Monocrystalline silicon resonant pressure transmitter uses the principle of resonant frequency change in monocrystalline silicon:
1. Micro resonators are processed on the monocrystalline silicon diaphragm.
2. The pressure causes the deformation of the diaphragm, resulting in the stress change of the resonator.
3. Stress change changes the vibrational frequency of the resonator.
4. After measuring the resonant frequency change, calculate the pressure value through the algorithm.
Advantages:
1. High precision
2. Good long-term stability, small drift, suitable for long-term measurement.
3. Strong anti-interference ability, insensitive to electromagnetic and environmental interference.
4. Suitable for high temperature, high pressure and harsh environment.
Disadvantages:
1. High manufacturing cost and high price.
2. The response speed is slightly slow, suitable for static or quasi-dynamic measurement.
3. Complex design and calibration.
Application scenario
Applications that require high accuracy and reliability, such as oil and gas pipelines, aerospace pressure measurement.
• Metrology and research equipment.
1.Coriolis mass flowmeter
There are two types of mass flow measurement: direct (direct measurement of fluid mass flow) and indirect (measurement of mass flow through a combination of volume flowmeters and densitometers). Coriolis mass flowmeters are direct type.
2. Working principle
The fluid enters the mass flow meter, and there are two sections of the fluid with countercurrent at both ends. By giving the pipeline a certain frequency of vibration (rotational angular velocity), the Coriolis force generated will form a torque, which is proportional to the passing mass, so the mass flow rate of the fluid through the pipeline can be measured.
The Coriolis force is a hypothetical force generated by inertia in a rotating reference frame, which is used to describe the deviation of an object's motion path. The direction of the Coriolis force is perpendicular to the direction of the object's motion and the direction of the axis of rotation. For example, in a rotating system like Earth, the Coriolis force has a significant effect on atmospheric and ocean flows. The Coriolis force deflects the wind to the right in the northern Hemisphere and to the left in the Southern Hemisphere. This deflection effect plays a key role in the formation of cyclones and anticyclones.
3. Coriolis mass flowmeter characteristics
① High measurement accuracy, direct measurement of mass flow, not affected by temperature, pressure factors.
② Sensitive to external vibration interference, the vibration of the pipeline should be eliminated.
③ The gas-liquid mixture or low-density gaseous fluid can not be measured, so the gas-liquid mixture in the pipe should be avoided during installation. For liquid media, the flow meter should be in the vertical pipe section/low point to avoid back pressure vaporization or pipeline dissatisfaction; For the gas medium, the flowmeter cannot be placed at a local low point to avoid the measurement error caused by the accumulation of liquid in the measuring tube.
④There is no requirement for the front and back straight pipe sections;
⑤ The price is expensive;
⑥Before and after the installation of the globe valve, convenient for zero correction.
The measurement interface of guided wave radar is based on the difference in dielectric constant of the medium and the principle of electromagnetic wave reflection.
1. Electromagnetic wave reflection mechanism:
The electromagnetic waves emitted by guided wave radar will partially reflect when encountering different media. The intensity of this reflection depends on the difference in dielectric constant between adjacent media.
A medium with a high dielectric constant will reflect stronger signals. For example, the dielectric constant of water (≈ 80) is much higher than that of oil (≈ 2-4), so the reflected signal is very obvious at the oil-water interface.
2. Signal distribution:
Electromagnetic waves first encounter the liquid surface (such as the top of an oil reservoir), where they undergo their first reflection.
The remaining electromagnetic waves continue to propagate until they reach the oil-water interface, resulting in a second reflection.
After receiving two reflected signals, the instrument calculates the liquid level height and interface height separately based on the time difference and signal strength.
3. Dual interface measurement:
For oil-water mixtures, guided wave radar can simultaneously measure the top oil level position and the bottom oil-water interface height
How does the liquid thermal mass Flow Sensor work?
Thermal mass flow sensors use the thermal characteristics of a liquid to measure its mass flow. As shown in Figure 1, heat is introduced into the flowing liquid through a heater, and the (temperature) sensor measures how much heat is absorbed by the liquid. In this type of thermal mass flow meter for liquids, the heater and sensor surround the stainless steel main duct with no moving parts or obstructions.
Liquid Mass Flow Controller:
Liquid flow control can be achieved by integrating a control valve into the liquid mass flow meter body or by adding a separate control valve.
Where are liquid thermal mass flowmeters and controllers used?
Quantitative feeding of lubricants in Aircraft Manufacturing - The liquid thermal mass flowmeter is used to monitor the quantitative feeding of borehole oil in the drilling of aircraft fuselage parts.
The principle of differential pressure transmitter for flow measurement is based on Bernoulli equation and differential pressure-flow relationship in fluid mechanics.
Principle statement
Differential pressure transmitters calculate flow by measuring the difference in pressure produced by a fluid before and after a special device in the pipe, such as a throttling device. According to Bernoulli's equation, when a fluid passes through a throttling device in a pipe (e.g., orifice plate, venturi tube, nozzle), there is a pressure difference between the front and back of the throttling device due to the change in flow rate. The pressure difference is related to the flow rate of the fluid.
Calculation formula
The relationship between the pressure difference measured by the differential pressure transmitter and the volume flow rate can be expressed by the following formula
Compatible hardware
Differential pressure transmitters need to be used with the following hardware when measuring flow:
1. Throttle device: used to produce pressure difference in the pipeline. Common throttling devices include:
• Orifice plate: A simple sheet with a small hole in the center, suitable for most fluid media.
• Venturi pipe: shrinkage-expansion pipe, low pressure loss, suitable for high-precision measurement.
• Nozzle: Suitable for high flow rate fluid, pressure loss is smaller than the orifice plate.
2. Flow calculation device: used to convert the electrical signal output by the differential pressure transmitter into a flow signal. This can be achieved by a flow integrator or PLC in an industrial control system.
3. Pipes and fittings: pipes and fittings for installing and fixing differential pressure transmitters and throttling devices.
The selection basis of throttling device
The selection of the appropriate throttling device requires consideration of the following factors:
1. Fluid characteristics: Different devices are suitable for different fluids (such as liquid, gas, steam).
2. Measurement accuracy: For high-precision measurement, venturi tube or nozzle is more suitable.
3. Pressure loss requirements: If low pressure loss is required, venturi or balance flowmeter is a better choice.
4. Cost and maintenance: hole plate cost is low, but maintenance is more frequent; Venturi tubes and nozzles are expensive but easy to maintain.
Shaanxi Nuoying Automation Instrument Co., Ltd. is an enterprise integrating research, design, production and sales of level instruments. It is a high-tech entity that has grown up relying on the intensive high-tech talents and strong technical force of Xi 'an University of Posts and Telecommunications. At present, we have more than 60 products in five series, such as radar level meter, RF admittance level meter, level switch, pressure meter and flow meter.
The following are the product classification details of these five series for reference
Level meter
● 80G radar level meter
● Tuning fork level switch
● 26G radar level meter
● Microwave level switch
● Guided wave radar level meter
● RF admittance switch
● RF admittance level meter
● RF capacitor switch
● Ultrasonic level meter
● Stop spinning material level switch
● Magnetic level meter
● External ultrasonic switch
● Tuning fork densitometer
Pressure instrument
● Monocrystalline silicon differential pressure transmitter
● Monocrystalline silicon high static differential pressure transmitter
● Monocrystalline silicon absolute pressure transmitter
● Monocrystalline silicon pressure transmitter
● Monocrystalline silicon flange pressure transmitter
● Single crystal silicon single flange liquid level transmitter
● Monocrystalline silicon single flange remote transmitter
● Monocrystalline silicon double flange remote transmitter
Flow meter
● NYRV- Precession vortex flowmeter
● NYLD-WL Turbine flowmeter
● NYLUGB vortex flowmeter
● NYLZ metal tube float flowmeter
● NY-LD pipe type electromagnetic flowmeter
● NYMF600 Mass flowmeter
● IRGA gas ultrasonic flowmeter
There are five common signal output types for sensors in level switches: relay output, two-wire output, transistor output, contactless output and NAMUR output. Among them, relay output is the most widely used, transistor output and contactless output are rarely involved, and two-wire output and NAMUR output are mainly used in intrinsically safe systems for the purpose of intrinsic safety. So what is the difference between two-wire output and NAMUR output in terms of application?
The two-wire system is a communication and power supply method relative to the four-wire system (two power supply lines and two communication lines). The power supply line and the signal line are combined into one, and the two lines realize communication and power supply. The two-wire instrument is a line without a power supply, that is, they do not have an independent working power supply. The power supply needs to be introduced externally, usually for the safety barrier to power the sensor, and the signal it transmits is a passive signal. The two-wire system generally uses 4~20mA DC current to transmit signals. The upper limit of 20mA is due to the explosion-proof requirements: the spark energy caused by the 20mA current on and off is not enough to ignite the gas. The reason why the lower limit is not 0mA is to detect line breakage: it will not be lower than 4mA during normal operation. When the transmission line is disconnected due to a fault, the loop current drops to 0. 2mA is often used as the line break alarm value, and 8mA and 16mA are used as the level alarm values.
The NAMUR standard first entered China in 2009. It was originally used in the proximity switch industry, so its working principle is defined by the proximity switch. Its working principle is: the sensor needs to provide a DC voltage of about 8V. According to the distance of the metal object approaching the sensor, a 1.2mA to 2.1mA current signal will be generated. The typical value of the calibrated switch current is 1.55mA. When the current changes from low to high or equal to 1.75MA, an output signal change (from 0 to 1, or from OFF to ON) will be generated. When the current changes from high to low and is lower than 1.55mA, an output signal change (from 1 to 0, or from ON to OFF) will be generated. In this way, it can be used to check whether the metal object is approaching.
From the working principle of NAMUR, it can be seen that it is similar to the two-wire output. It provides power to the sensor through the isolation barrier (usually 8.2VDC, two-wire is 24VDC) and detects its current signal. The NAMUR output detection point is usually ≤1.2mA and ≥2.1mA (different companies set different detection points), and the detection point of the two-wire output is generally 8mA and 16mA. The switch signal is converted through the isolation barrier and finally output to the DCS or PLAC control room.
The difference between it and the two-wire system is that its current and voltage are smaller, and the power requirement of the safety barrier used is lower, but relatively, its price is much more expensive than that of the two-wire output.
At present, in China, the two-wire output is more widely used in the intrinsic safety system, and the NAMUR output is less used. The reasons are nothing more than the following two points:
1. The NAMUR signal output system is expensive;
2. The intrinsically safe two-wire output can completely replace the NAMUR output, and its price is cheaper.
Intro
The air separation unit is a supporting project of public works, providing nitrogen, oxygen and argon for construction for each unit, power station and auxiliary facilities. The main product of nitrogen is used for purging, sealing, displacement and security. The air cooling tower is an air pre-cooling system, the main function is to compress the gas into the air cooling tower to be cooled and washed by water. The upper part of the air cooling tower is cooled by the low temperature water cooled by the chiller (RU1101 ~ 1103), and the lower part is cooled by the cooling water of the self-circulating water system. The top of the air cooling tower is provided with a free water separation device and a unique anti-flooding device to prevent the free water in the air from being brought out.
Inspection process
The double-flanged liquid level gauge was checked, and the positive pressure side capsule was inelastic, with rust and scale attached to the surface. After cleaning the rust and scale, it was found that the capsule had pinpointed small holes. The indicator returned to normal after replacing the level gauge.
Cause analysis
The double flange liquid level gauge cartridge is damaged, and the lack of silicone oil causes abnormal fluctuation of liquid level, triggering high interlock and causing air compressor unloading. The air cooling tower cools the air compressed by the air compressor and cleans the dust, the water contains dust and impurities, the positive pressure side flange of the double flange level meter is relatively static, and the dust and impurities will precipitate on the surface of the diaphragm, without considering the scaling problem of the diaphragm. There is no set period to discharge and flush the pressure inlet and capsule on the positive pressure side.
Preventive measures:
1, based on the safety instrument system, according to SIL grading, interlocking grade, device importance, production impact, improve the classification of instrument equipment. Allocate manpower and funds according to instrument grade, and tilt management toward important instrument equipment.
2. Promote the data improvement and application of the instrument failure database, record the failure of the instrument equipment, realize the automatic classification statistics of overhaul and maintenance, establish the whole life cycle management of the instrument equipment, and provide reliable data support for the maintenance and overhaul of the instrument.
3, improve the preventive maintenance program of key units, the interlock instrument of the attached system of key units is included in the inspection content. And explore the air cooling tower level gauge for preventive discharge cycle.
The End
