CASES

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   

Working principle： When the fluid flows through the orifice plate of the orifice plate flow meter device, the cross-sectional area decreases, the velocity increases, and the corresponding pressure decreases, and the degree of reduction is proportional to the fluid velocity of the flow state. Therefore, the flow rate can be calculated by detecting the pressure difference, and then the flow rate can be calculated.                                                                                      Operating condition: Outlet flow of lean methanol water cooler, measure the flow of injected methanol, medium: lean methanol, temperature: 42℃, pressure 4.31Mpa, this table is only for display, without linkage.   Fault phenomenon: Indicated fluctuation   Fault analysis: 1. Whether the pressure guide pipe is blocked; 2. Whether the three valve groups are blocked; 3. Transmitter itself; 4. Flexible leakage point; 5. Transmitter zero drift; 6. The transmitter range is not set correctly; 7. Process issues.   Treatment method: 1. First check the live joint of the pressure guide pipe and the sealing position of the three valve groups and no leakage is found. 2. Close the positive and negative pressure root valves and open the transmitter blowdown plug for blowdown. At this time, it is not found that the medium is not flowing smoothly, and the possibility of blocking the pressure guide tube and the three valve groups is excluded. 3. Open the balance valve of the three valve groups of the flow meter and remove the blowdown screw plug. At this time, the check finds that the central control still has the flow indication when the meter head indicates zero. At this time, a multimeter is used in series to measure the output of the transmitter to 8.01mA, and the reason is judged to be the transmitter itself. 4. At the same time, it can be judged that the measurement capsule and converter display are normal through the on-site scheduling check process. 5. Remove the differential pressure transmitter and disassemble it. It is found that the terminal block is seriously corroded. 6. Clean up the corrosive substances in the differential pressure transmitter, check whether the circuit board components are damaged, replace the terminal block of the differential pressure transmitter, and re-weld the terminal block with a wire. 7. Assemble the differential pressure transmitter, and check its zero output normal through the power supply. 8. Differential pressure transmitter back assembly. 9. Before installation, check whether there is debris in the pipe to prevent debris from blocking or damaging the standard orifice plate.                                                                                                                            Thank   You                                                           

      Ultrasonic level meter is widely used for level measurement in chemical industry, water treatment, water conservancy, food, grain and other industries. The product has the characteristics of safety, cleanliness, high precision, long life, stability and reliability, easy installation and maintenance, simple reading and so on. Ultrasonic level meter is a digital level meter controlled by microprocessor. In the measurement, the pulse ultrasonic wave is emitted by the sensor (transducer), and the sound wave is received by the same sensor after being reflected by the surface of the object and converted into an electrical signal. The distance between the sensor and the measured object is calculated by the time between the transmission and reception of the sound wave. Due to the non-contact measurement, the measured medium is almost unrestricted, and can be widely used in the height measurement of various liquid and solid materials. Most sewage plants will use inverter, motor, centrifuge and other equipment with interference sources. These interference factors force the measurement of the ultrasonic level meter around it to be non-standard. When the measurement is not correct, it is the on-site staff who are worried. In order to allow the on-site staff to more accurately grasp the real-time level of the water level, the following solutions are summarized for everyone, so that you can easily solve the problem of ultrasonic level electromagnetic interference.                                                    Phenomenon Ultrasonic level meter data beat irregular, or simply show no signal;     Solution: 1. The ultrasonic level meter must be reliably grounded. After grounding, some interference on the circuit board will run away through the ground wire. This grounding is to be grounded separately and cannot be shared with other equipment. 2. The power supply can not be the same power supply as the inverter and the motor, nor can it be directly generated from the power system. 3. The installation location should be far away from the frequency converter, variable frequency motor, and high-power electric equipment. If it can not be far away, it is necessary to install a metal instrument box on the outside of the level meter to isolate the shield, and the instrument box also needs to be grounded.                                                                                                       

                                                      Fault category: Hardware failure   Operating conditions: The liquid level display suddenly fluctuates several times, and the display returns to normal after zero correction.   Fault symptom description: During the process control and monitoring panel, it was found that the liquid level display of the remote liquid level gauge in the fractionation zone suddenly pulsated (the liquid level fluctuated several times before, and the liquid level display returned to normal after the air calibration zero). After receiving the process notice, the instrument was disassembled and checked on site.   Fault causes and judgment ideas: 1.The liquid medium in the buoy contains impurities 2. The buoy body is damaged 3. The transmitter sensor is faulty   Effective troubleshooting methods and preventive measures:   1. Contact the process to close the positive and negative pressure valve of the liquid level gauge, open the guide to discharge the medium in the buoy, and observe whether the medium contains foreign matter or whether the medium is cloudy. 2. Disassemble the buoy to check whether there is any foreign object attached to the buoy or whether there is any damage to the buoy body. 3. Check whether the cable to the liquid level gauge is faulty, such as virtual connection. 4. After checking step by step according to the above steps, no abnormal situation is found, and it is judged that the float liquid level gauge sensor is faulty. Replace the sensor and set relevant parameters. After the liquid level gauge is put into use, the liquid level indicator returns to normal.                                                                                                                                                                  The End

                                                                               Fault category: The liquid level indication is inaccurate and fluctuating   Operating conditions: Measure the depth of the liquid level of the initial rainwater tank (usually the main medium is road rain and steam drizzle), normal temperature, normal pressure, and atmospheric exposure. When the liquid level is high, the staff manually starts the P-4480 pump and pumps the liquid level to the water supply   Fault symptom description: Inaccurate/fluctuating level indication.   Fault causes and judgment ideas: 1. First check the easy to handle, check whether the cable is loose, and check whether the junction box is flooded. 2. Check whether there is noise interference. 3. Whether there are floating and moving things on the water surface of the pool. 4. Whether there are obstacles around the probe. 5. Whether there are water droplets where the probe emits sound waves.   Treatment method: 1. Open the junction box and check whether the transmitter cable is securely connected and water is not flowing. 2. Check the liquid level in the pool: After inserting the steel pipe into the bottom of the pool, mark the depth of the pool surface with a marker 1. After drawing out the steel pipe, mark the water mark 2. Then use the tape measure to measure the length of the two marks, and then use the tape measure to measure the height of the pool surface to the installation point, that is, the blind area. 3. Remove the probe, find a small amount of water beads on the probe, dry with dry noodles. 4. Check the installation hole and find that there is a spider web near the probe before the sound wave is emitted. Remove the spider web and install it well. 5. View the display value The liquid level gauge is consistent with the measured value, and the DCS display data is just consistent.   Preventive measures: 1. The ultrasonic level meter should be cut off before maintenance. 2. Check whether the cable sealing plug is tight and the cover is properly covered. 3. The installation place of the ultrasonic level meter should be equipped with protective measures for shade and rain.                                                                                                                            The End 

Working principle The switch structure of float level controller is mainly designed and produced based on the principle of buoyancy and static magnetic field. The position of float ball with magnet (referred to as float ball) in the measured medium is affected by buoyancy. In the place of use, the change of the liquid level causes the change of the position of the magnetic float. Magnets and sensors (reed switches) in the float act to generate a switching signal to start or stop the pump. Similar to the float level meter principle, but the float level meter output is a continuous signal, while the float level controller output is a discrete switching signal.   Fault phenomenon The float switch of pump No. 3 in sewage M pool cannot be started normally, and the float level controller does not operate when the liquid level reaches the specified water level.   Fault analysis 1. Check whether the wiring in the junction box is loose and whether the wiring screws are off 2. Check whether the junction box is flooded or damp 3. Check whether the wiring is correct and whether the cable is damaged 4, check the pool for debris or cable is not straightened out 5, check whether the surface of the float is attached to a lot of dirt 6. Check whether the float ball is sealed and there is no water in the float ball 7. Check whether there is abnormal sound in the float   Treatment method 1. Open the junction box and find that there is no moisture, water and other conditions inside, and observe that there is no screw loosening in the wiring. 2, check the wiring is correct, there is no foreign matter in the pool, the cable is not damaged, no knot 3. After the float was put forward, it was found that the float was broken and could not be repaired, so the maintenance measure was determined to replace the float level controller 4. Replace the float level controller 5, adjust the float to the appropriate position after normal operation                                                             Thank you for reading, any questions are welcome to discuss with us.                                                                          

  Summarization   Vortex flowmeter is a flow measurement instrument based on the Karman vortex flowmeter principle, also known as vortex flowmeter or Karman vortex flowmeter. It is mainly used to measure the volume flow of gas, steam or liquid in various pipelines. It is a new type of flow meter commonly used in industrial control, energy metering and energy saving management, and is widely used in industrial production, energy metering, environmental protection, transportation and other fields.   Working principle   Vortex flowmeter is an instrument that uses regular vortex stripping phenomenon to measure fluid flow. When a non-streamlined column (cylinder or triangular column) is vertically inserted into the fluid as a vortex generator. When the Reynolds number reaches a certain value, there will be two columns of alternating vortices in the downstream of the column, because these vortices are like street lights next to the street, so it is called "vortex street", this phenomenon was first discovered by Karman, also known as "Karman vortex street".   At the back of the object are neatly arranged vortices that turn in opposite directions along two parallel lines.   The number of these vortex rows, the vortex frequency, is proportional to the flow rate of the fluid. By measuring the frequency of the vortex, the flow rate of the fluid can be deduced, and the flow rate of the fluid can be calculated.   Product picture      Peculiarity   Vortex flowmeter is characterized by high precision, wide measuring range, no moving parts, no mechanical wear, easy maintenance, small pressure loss, energy saving effect is obvious. However, the vortex flowmeter is not suitable for low Reynolds number, for high viscosity, low flow rate, the use of small diameter has limitations, the flowmeter installation should have enough length of the straight pipe section, the length of the upstream and downstream straight pipe section is not less than 20D and 5D, and should try to eliminate vibration.   The frequency of vortex in vortex flowmeter is not affected by temperature, pressure and viscosity, so it has high measurement accuracy.     Application field   The application range of vortex flowmeter is quite wide, mainly including the following areas:     Industrial production: In metallurgy, power, coal, chemical, petroleum and other industries, vortex flowmeters are used to measure and control the flow of various fluids (including gas, liquid and steam) to meet the needs of the production process.   Energy metering: In the field of energy measurement, vortex flowmeters can be used to measure the flow of primary energy (such as coal, crude oil, coal bed methane, liquefied petroleum gas and natural gas) and secondary energy (such as electricity, coke, artificial gas, refined oil, liquefied petroleum gas, steam) and energy-carrying working medium (such as compressed air, oxygen, nitrogen, hydrogen, water). It provides an important basis for scientific management of energy, realizing energy saving and consumption reduction and improving economic benefits.   Environmental protection: In the field of environmental protection, vortex flowmeters can be used to monitor and control the discharge flow of flue gas, waste liquid, sewage, etc., which helps to improve the quality of atmospheric and water resources.   Transportation: In the field of transportation, vortex flowmeter is a key tool for control, distribution and scheduling in pipeline transportation, and can achieve accurate control and management of the transportation process by measuring the flow of fluid in the pipeline.   In summary, vortex flowmeter is a kind of flow measuring instrument with high precision, wide range, good stability, strong adaptability and wide application. With the continuous development of industrial automation and technological progress, the application prospect of vortex flowmeter will be broader.                                                                                                                                                                                                                                                        The  End    

Piezoresistive pressure transmitter as below picture is characterized by its small size and simple structure. The sensitivity coefficient of diffusion resistance is dozens of times that of metal strain gauge, and can directly measure small pressure changes. In addition, piezoresistive pressure transmitters also have good dynamic response and low hysteresis, which can be used to measure pulsating pressures of several thousand Hertz or even higher. This is a relatively rapid development, very widely used pressure transmitter.     Capacitive pressure transmitter adopts differential capacitance as detection element, which mainly includes measurement and conversion amplification. The differential signal is converted into differential capacitor signal by the central pressure sensing diaphragm and the left and right curved capacitor plate, and the central pressure sensing diaphragm forms a capacitor with the left and right curved capacitor plate respectively. The differential pressure causes the central pressure sensing diaphragm to produce displacement, so that the distance between the movable electrode and the left and right fixed electrodes is no longer equal, forming a differential capacitance, and the relative change value of the differential capacitance is linear with the differential pressure. Due to the mechanical transmission mechanism without lever inside the whole capacitive differential pressure transmitter, it has the characteristics of high precision, high stability and high reliability, and its accuracy level can reach 0.2, which is a kind of transmitter commonly used in industry.   The piezoelectric pressure transmitter uses the piezoelectric effect of the piezoelectric material to convert the measured pressure into an electrical signal. It is a commonly used sensor in dynamic pressure detection, and is not suitable for measuring slowly changing pressure and static pressure. The vibration frequency pressure transmitter uses the relationship between the resonant frequency of the pressure sensing element itself and the pressure to detect the pressure by measuring the change of the frequency signal. This kind of sensor has a variety of forms such as vibrating drum, vibrating string, vibrating film, quartz resonance, etc. The instrument has small size, output frequency signal, good repeatability and vibration resistance. High precision, suitable for gas measurement.   Application: Pressure transmitters are widely used in various industrial fields, such as petroleum, chemical, metallurgy, electric power, pharmaceutical, water treatment, etc., for measuring and controlling the pressure of various fluids to ensure the stability and safety of the process.   They can measure a wide range of pressures from tiny to extremely high, with high precision, high stability, high reliability and long life. In addition, according to the different measurement principles and application scenarios, pressure transmitters can also be divided into a variety of types, such as differential pressure transmitters (used to measure the difference between two pressures), absolute pressure transmitters (used to measure the absolute pressure relative to vacuum), gauge pressure transmitters (used to measure the pressure relative to atmospheric pressure) and so on.                                                                                                           The End 

The device that can detect the pressure value and provide a remote signal is collectively referred to as the pressure transmitter, which is a sensor commonly used in industrial automation process control to measure the pressure of a gas or liquid, and convert this pressure value into a measurable and transferable electrical signal.   These electrical signals are typically standard current or voltage signals, such as 4-20mA current signals or 0-10V/0-5V voltage signals, to facilitate remote transmission, display, recording or control in industrial automation, process control, monitoring and measurement systems.   It can meet the requirements of centralized detection and control of automation system, and is widely used in industrial production.   Composition of pressure transmitter: The pressure transmitter usually consists of a pressure sensitive element (such as a strain gauge, capacitor diaphragm, piezoresistive chip, etc.) and a signal processing circuit. When the measured medium acts on the pressure sensitive element, it will cause some physical change in the element (such as resistance change, capacitance change, resonant frequency change, etc.), which is then converted into an electrical signal. The signal processing circuit is responsible for amplifying, linearizing, and temperature compensating this electrical signal to output a stable and accurate pressure value.   Types of pressure transmitters The structure of the pressure transmitter is varied, according to the working principle, there are strain type, piezoresistive type, capacitance type, piezoelectric type, vibration frequency type and so on. The following is a brief introduction to several commonly used pressure transmitters. The strain gauge pressure transmitter has a large measuring range, the measured pressure can reach hundreds of mpa, and has good dynamic performance, suitable for rapidly changing pressure measurement. But there are more obvious temperature drift and time drift, this instrument is more used in the general requirements of dynamic pressure detection; Piezoresistive pressure transmitter is manufactured according to the piezoresistive effect principle, and its pressure sensitive element is the diffusion resistance made of integrated circuit technology on the substrate of semiconductor material. When it is subjected to external force, the resistance value of the diffusion resistance changes due to the change of resistivity.                                                                                Strain gauge pressure transmitter