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Remote type electromagnetic flow meter adopts the principle of time difference measurement: one probe transmits a signal through the pipe wall, the medium, and the other side of the pipe wall, and is received by another probe.At the same time, the second probe also transmits the signal and is received by the first probe.Due to the influence of the flow velocity of the medium, there is a time difference Δt between the two.According to the calculation, the conversion relationship V=(C2/2L)×Δt between the flow velocity V and the time difference Δt can be obtained, and the flow rate value Q can be obtained.

Remote type electromagnetic flow meter has many advantages: high precision; large measuring range; measurement results are not affected by conductivity, pressure, temperature and viscosity; it is not in contact with medium, especially suitable for measurement of corrosive media; simple installation and low cost ;can be installed on existing pipelines without cutting off process pipelines;no spoiler, no need to reduce the diameter, no leakage, low cost; at the same time, the probe of remote type electromagnetic flow meter produced in China can cover the pipe diameter of DN6 ~ DN6500 range,which has the advantages of high cost performance and timely service of domestic products.

Application direction of remote type electromagnetic flow meter: the current industrial flow measurement generally has the problem of large diameter and large flow measurement difficulty. This is because the increase of the measurement pipe diameter will bring difficulties in manufacturing and transportation, and the cost will increase and the energy loss will increase.and the remote type electromagnetic flow meter can avoid these shortcomings. Because all kinds of electromagnetic flow meters can be installed outside the pipe, non-contact flow measurement,the cost of the instrument is basically independent of the diameter of the pipeline under test, while other types of products with the increase in caliber, the cost is greatly increased. Compared with the functional price of other types of flow meters with the same function, the larger the diameter, the better, and it is considered to be a better large-diameter flow measuring instrument. Remote type electromagnetic flow meter adopts advanced DSP technology and double UP high-speed processor, which increases the sampling frequency to 70ms and can be used to measure the change of fluid flow in a very short time.By erecting metal guided wave plate between pipeline and probe, the temperature of medium is reduced from 450℃ to below 200 ℃,which makes measurement possible, and has unique applications in the petrochemical industry, the nuclear power industry, and the heat transfer oil field.And the energy calculation function is adopted, and the temperature signal can be introduced while measuring the flow rate to obtain the energy parameter.  

1.What kind of communication line should be used for the 485 bus?

Internationally accepted shielded twisted pair must be used. The recommended type of shielded twisted pair is RVSP2*0.5 (two-core shielded twisted pair, each consisting of 16 strands of 0.2mm wire). The use of shielded twisted pairs helps to reduce and eliminate the distributed capacitance generated between the two 485 communication lines and the common mode interference generated around the communication lines.

Most of the engineering contractors are accustomed to using 5 kinds of network lines or over 5 kinds of network lines as 485 communication lines, which is wrong. This is because:

(1) The common network cable has no shielding layer and cannot prevent common mode interference.

(2) The network cable is only 0.2mm square, and the wire diameter is too thin, which will result in a reduction in transmission distance and a reduction in the number of devices that can be attached.

(3)The network cable is a single-strand copper wire that is easily broken compared to a multi-core wire.

2.Why is it grounded?

The 485 transceiver will operate normally when the specified common mode voltage is between -7V and +12V. Exceeding this range will affect communication and severely damage the communication interface. Common mode interference increases the above common mode voltage. One of the effective means to eliminate common mode interference is to use the shielding layer of the 485 communication line as the ground line, connect the devices in the network such as implements and computers, and reliably connect to the earth from one point.

3.How should the 485 communication line be connected?

Keep the communication lines away from high-voltage wires as much as possible, not in parallel with the power cables, or bundle them together.

4. Why should the 485 bus adopt a hand-in-hand structure instead of a star structure?

The star structure produces a reflected signal that affects 485 communications. The length of the branch line from the bus to each terminal device should be as short as possible, generally not exceeding 5 meters. If the branch line is not connected to the terminal, there will be a reflected signal, which will cause strong interference to the communication and should be removed.

5.Can there be contacts between devices on the 485 bus?

Use the same cable in the same network system to minimize contact in the line.Make sure the joint is well welded and tightly packed to avoid loosening and oxidation.A single and continuous signal channel is guaranteed as a bus.

6. What is common mode interference and differential mode interference? How to eliminate interference on the communication line?

The 485 communication line consists of two twisted pairs of wires that transmit signals through the voltage difference between the two communication lines, so it is called differential voltage transmission.

Differential mode interference is transmitted between two signal lines ,which belongs to symmetric interference. The method of eliminating differential mode interference is to add a bias resistor in the circuit and use a twisted pair.

Common mode interference is transmitted between the signal line and ground,which belongs to the asymmetric interference. Methods to eliminate common mode interference include:

(1) Use shielded twisted pair and effectively ground.

(2) The galvanized tube shield should also be considered in the strong electric field.

(3) Keep away from the high voltage line during wiring, and do not bundle the high voltage power line and signal line together.

(4) Do not share the same power supply with the electronic lock.

(5) Adopt linear stabilized voltage supply or high-quality switching power supply  (ripple interference is less than 50mV).

7. Under what circumstances should the terminal resistance be added to bus 485?

Under normal circumstances, it is not necessary to add the terminal resistance. Only when the 485 communication distance exceeds 100 meters,the terminal resistance should be added at the beginning and end of 485 communication.

8. How to extend the communication distance of 485?

One of the specifications of the 485 network is 1.2 km in length and the number of 32 nodes.If this limit is exceeded, a 485 repeater or 485 hub must be used to extend the network distance or number of nodes.

With a 485 repeater or 485 hub, a large 485 network can be divided into several network segments. A 485 repeater or 485 hub is like a "bridge" between the 485 network segments.Of course, each network segment still follows the above 485 specification, which is 1.2 kilometers in length and the number of 32 nodes.

The 485 hub is used to construct the star 485 network.The 485 hub is a broad extension of the 485 repeater concept.It not only solves the problem of multi-forking, but also solves the problem of isolation between network segments, that is, there is a problem in one network segment (such as short circuit, etc.), which does not affect other network segments, thereby greatly improving the security and stability of large networks.

We can understand the benefits of the star-shaped cabling network from the development of the LAN from the bus type to the star type. Similarly, the star 485 network composed of 485 concentrator will also be a direction for the development of the 485 network.

Industrial wastewater discharge includes pressure piping and open channels, pressureless pipelines and other forms of non-pressure discharge.The sewage flow meter discharged in the form of a pressure pipe is convenient to measure, and can be measured by a pipe flow meter such as an electromagnetic type, a laser type, or a venturi differential pressure type. At present, the sewage discharge in China mainly adopts the form of discharge without pressure open channel, and the sewage open channel flow meter is designed to solve the problem of sewage measurement in this form of discharge.

1. Working principle and composition of open channel flow meter

Pasteur trough and thin-walled weir are commonly used as measurement methods for open channel sewage flow.Its principle belongs to the throttling flow measurement technology. The direct object of measurement is the water level difference between upstream and downstream of the throttling device. According to the water level difference, the instantaneous flow on the cross section can be calculated.

The open channel sewage flow meter is composed of a measuring weir (flow measuring flume), liquid level sensor and secondary instrument. The work of forming the head (standard flow), measuring the height of water level and calculating the flow rate are completed respectively.

2. Types and scope of weirs and troughs

Water-measuring weir

A weir is a device that intercepts the flow of water and allows it to overflow from the top. There are many kinds of weirs: According to the thickness, it can be divided into thin-walled weirs (whose thickness is less than 0.67 times the geometric head), suitable weirs and wide-crested weirs, etc.According to the cross-section shape, it can be divided into triangular weir, trapezoidal weir, equal-width weir, etc. According to the connection form of jet and downstream water level, it can be divided into submerged weir and non-submerged weir.Thin wall triangular weir, thin walled trapezoidal weir and thin wall rectangular weir are commonly used.Under certain conditions, for a certain thin-walled weir, the flow rate has a certain function relationship with the geometric head height, and the sewage flow can be measured accordingly. When measuring the flow with water weir, the loss of water head is large, which is suitable for measuring the sewage with little suspended substance and non-fibrous substance.

Flow-measuring flume

Wide-crested weir with lateral contraction is called flume when the height of weir bar is zero. It is a special deformation of weir. It can be divided into short throat flume (Pasteur flume), no throat flume (Sun flume) and long throat flume.Commonly used in open channel sewage flow metering is Pasteur trough.Under certain conditions, for a certain Pasteur trough,there is a certain functional relationship between the flow and the upstream water level height,according to which the sewage flow can be measured. When measuring flow with flow measuring trough, head loss is small and water quality conditions are wide. When measuring sewage, aquatic organisms on the trough wall should be cleaned up in time to keep the trough wall smooth.

3. Liquid level sensor

There are mainly ultrasonic liquid level sensors, pressure type liquid level sensors, capacitive liquid level sensors, float type liquid level sensors and so on.These level sensors have their own characteristics  and different application ranges.

Ultrasonic sensor is a specific application of ultrasonic ranging method. Its characteristics are to achieve non contact flow and wide application range, but the required liquid is reflected well by ultrasonic wave. If there is abnormal reflection of foam, debris and biological mud, it will bring greater error. In addition, ultrasound is also affected by weather factors such as temperature, air pressure and wind speed. Although these factors can be compensated, the structure of the instrument is complex and the cost is high.

The characteristic of pressure type liquid level sensor is simple installation. However, the specific gravity of the tested liquid is basically constant, so its application in sewage with large variation of specific gravity is limited. In addition, attention should be paid to the smooth opening of the pressure measuring hole when used in sewage.

The characteristic of capacitive hydraulic sensor is that there are no moving parts, but the mechanical strength and dielectric properties of insulating medium are difficult to take into account, and the change of capacitance caused by the influence of temperature reduces the measurement accuracy. In addition, the electrode surface should be cleaned up in time when used in sewage.

The float liquid level sensor has the characteristics of low cost, not affected by water quality and wide application range, but it requires that the specific gravity of water body is basically constant, and attention should be paid to the effect of surface adhesives on the specific gravity of float.

4.Secondary instrument

Secondary instrument is an automatic device which can receive the voltage (current) signal of liquid level sensor and accumulate sewage flow based on it. It can not only give instantaneous flow, but also get cumulative flow. It can connect the recorder to observe the change of flow rate and the computer to realize the automatic flow monitoring.

The alarm function attached to the meter is significantly different from the insurance function, because the circuit of the additional alarm function part has many commonalities with the display of the meter, the power supply and the sensor, etc. It is necessary to emphasize that the failure of a common place may directly lead to the loss of alarm function.Therefore, in the case of a system that will cause significant consequences in the event of loss of control, an independent protective device must be provided as required.

If you want to achieve a more reliable, insurance-type alarm function, you should use bimetal or pressure instruments for protection, or use a complete set of electronic alarms from sensors to actuators.The instrument dedicated to electronic alarms, due to its simple function and structure, is relatively less reliable than the more complex display adjustment instruments.Most display adjustment instruments can be equipped with an alarm function.

Additional alarm functions are mainly implemented in the following ways:

1. Unsettable upper limit follow-up alarm function

This function means “to make an alarm action when the input value reaches the set value + full-scale direction—fixed value”. Take the XMTA 2311 0~300℃ meter as an example.The standard stipulates that the input value reaches the set value + (4% ~ 6%)×300, the alarm action should be made.If the meter setting value is 200℃, then the meter should make an alarm action when the input value is +12℃ to +18℃+ the instrument allows the setting error (212 to 218) ± 3℃.The default alarm action is the normally open contact closure of the alarm output relay.

2. Unsettable lower limit follow-up alarm function

This function means “to make an alarm action when the input value reaches the set value—starting range direction—fixed value”. Take the XMTA 2311 0～300℃ meter as an example.The standard stipulates that the input value reaches the set value—(4%~6%)×300, the alarm action should be made. If the meter setting value is 200℃, then the meter should make an alarm action when the input value is -12℃~ -18℃+ the instrument allows the setting error (182 ~ 188)±3℃. The default alarm action is the normally open contact closure of the alarm output relay.

3. Alarm function that can set alarm value

This function refers to the alarm action when the input value reaches the value that people intentionally set on the surface board, regardless of the upper limit, upper limit, lower limit and lower alarm. The default alarm action is the normally open contact closure of the alarm output relay (eg smart meter).

4. The instrument can also be used as a sound alarm output (special order)

In order to improve the anti-interference ability as much as possible, the position difference of the alarm bit is selected to be larger. Generally it is about 1% to 5% of the full scale.

5. Three-bit meter for alarm

Under normal circumstances, it is not advisable to use one bit of the three-bit meters for an alarm.If the upper limit control of the three-bit meter is used as the upper limit alarm, the action of the alarm is that the normally closed contact is closed again, that is,the meter is in an alarm state immediately after power up,and the default alarm action will be reversed.This is different from a meter specifically designed for alarms. If the upper limit alarm of the three-bit meter is used as the lower limit alarm or the lower limit alarm is used as the upper limit alarm, it is possible to make an alarm action when the instrument is powered on.

The ultrasonic flow meter adopts high-precision and ultra-stable double-balanced signal differential transmission and differential receiving digital detection technology to measure the sound wave transmission time in the forward and reverse flow directions, calculate the flow velocity according to the time difference, and has the characteristics of good stability, small zero drift, high measurement accuracy, wide range ratio and high anti-interference. At present, ultrasonic flow meters are mainly used in the following industries:

1. Petroleum industry:Mainly used for measuring medium such as high pressure water injection,circulating water, oil-water mixture, domestic water and sewage.

2. Metallurgical industry: Mainly used for measuring medium such as soft water for continuous casting, secondary cooling water for continuous casting, water for steelmaking equipment, oxygen lance water for converter, dust removal water for converter, vaporized soft water, semi-purified water, circulating water, domestic water and sewage.

3. Petrochemical industry: Mainly used for measuring medium such as production water, domestic water, circulating water, fire water and sewage.

4. Electric power industry: thermal power generation, hydroelectric power generation, nuclear power, mainly used for industrial water, raw water, intermediate water, circulating water, cooling water, boiler water, ash water, domestic sewage, chemical water and other media measurement.

5. Chemical Industry: Mainly used for the measurement of circulating water, chemical water, chemical slurry, drinking water, sewage and other media.

6. Coal mine/mine: Mainly used for groundwater, coal washing water, circulating water, sewage, etc.

7. Paper making industry: Mainly used for the measurement of circulating water, industrial wastewater, domestic water, domestic sewage and other media.

8. Water treatment industry:Mainly used for the measurement of domestic water and sewage.

9. Building construction: Mainly used for the measurement of circulating water in air conditioning.

10. Food and medicine: Mainly used for measuring small pipe runoff of ultrapure water, circulating water, drinking water, domestic sewage,industrial wastewater and other media.

11. Other industries: There are also a large number of applications in ultrasonic energy flow meters in energy-saving testing centers, water resources management, water supply and drainage associations, environmental protection departments, cigarette factories, fire protection, measurement and testing, on-site counterparts or departments. 

The orifice flow meter is a throttling device and is a differential pressure sensing element that measures flow.Equipped with differential pressure transmitter and realistic, recording, integrating and adjusting instruments, it can be used to measure, calculate and control the instantaneous flow rate and cumulative flow rate of liquid, steam and gas.

The throttling device has the advantages of simple structure, convenient installation, reliable use, low price, convenient maintenance and wide selection range (the measuring pipe diameter of the standard throttling device can be from 50 mm to 1200 mm, and the  diameter of the non-standard throttling device can be as small as 6mm, as large as 3000mm; the measuring temperature can be as high as 555°C; the pressure can reach 42MPa), and the standard throttling device also has the advantages of no need for separate calibration, etc.It is the most widely used and most mature product in flow meter, so it is widely used in electric power, chemical industry, metallurgy, petroleum, textile, military and other fields.

The throttling device is composed of a throttle part, a pressure taking device(including pressure taps, pressure pipes and valves, etc.) and matching flanges, sometimes including straight pipe sections that meet the standards.The standard throttle device has standard orifice, standard nozzle and standard Venturi tube. Standard orifice plates are angled (ring chamber or borehole) to take pressure, flange to take pressure, diameter to take pressure; Standard nozzles are  divided into nozzles and long-diameter nozzles according to their forms; standard Venturi pipes are divided into Venturi nozzles and Venturi pipes according to their forms (roughly cast or machined or rolled plates). Non-standard throttling devices include small aperture plate, 1/4 round orifice plate, round orifice plate,circular orifice plate, eccentric orifice plate, double orifice plate, concealed orifice plate, conical inlet orifice plate, etc. Other forms of throttle devices include pitot tube, uniform speed pipe, wedge, cone and so on.

When using a standard throttling device, the nature and state of the fluid must meet the following conditions:

(1) The fluid must be filled with pipes and throttling devices and flow continuously through the pipe;

(2) The fluid flow does not change or change very slowly over time;

(3) Fluid does not intersect through throttling parts;

(4) The fluid must be Newtonian fluid, ie physically and thermodynamically homogeneous, single-phase, or can be considered single-phase, including mixed gases, solutions and dispersive particles less than o. 1 m colloid.Solid particles having a uniform dispersion of not more than 2% (mass component) in the gas, or bubbles having a uniform dispersion of not more than 5% (volume component) in the liquid may also be regarded as a single-phase fluid, but the density thereof shall be an average density;

(5) Before the fluid flows through the throttling parts, the flow of fluid is an irrotational flow parallel to the axis of the pipeline.

Standard throttling devices are not suitable for flow measurement of moving and critical flows. The throttling device artificially causes throttling in the pipeline in which the medium flows. When the measured medium flows through the throttling device, a partial contraction occurs, the stream is concentrated, the flow rate is increased, the static pressure is lowered, and then the upstream and downstream of the throttle part are a static pressure difference is generated on both sides. This static pressure difference has a certain function relationship with the flow rate. The larger the flow rate, the larger the static pressure difference generated. Therefore, the flow rate can be measured by measuring the differential pressure.

The orifice flow meter is different from other flow meters in that the orifice flow meter is based on the parameter to design drawings and is finally processed. It is only necessary to select the orifice material according to the measurement medium.

There are many kinds of common flow meters suitable for measuring small flow, such as differential pressure, float type, volumetric type, thermal type, etc. Some of them are suitable for measuring medium and large flow,and are also suitable for measuring small flow,while others are specially designed for measuring small flow.

1. Float flow meter

The float flow meter is mainly composed of a float and a conical tube.The conical tube in the glass tube float flow meter is a glass tube; The conical tube in the metal tube float flow meter is made of metal with a fluid temperature of up to 180 ° C and a fluid pressure of 13 MPa.

The float flow meter is a medium and low precision meter. The basic error of the metal float flow meter is 1%~2.5%FS for the local indication type, 1%~4%FS for the remote transmission type; The small-diameter glass tube float flow meter is 2.5%~ 5% FS. Therefore, it is generally only applicable to flow monitoring and not for accounting measurement.

Glass tube float flow meter is only suitable for gas and liquid with high transparency, otherwise the height of float in conical tube is not easy to see. The metal tube floater flow meter has no such limitation.

The flow measurement range of the small-caliber float flow meter can be made very small,in which water is 0.3-3 L/h and air is 5-50 L/h.Miniature glass float flow meters, such as atmospheric samplers, on-line flowsheet analyzers and laboratory analyzers, are widely used in environmental protection, and their measurement ranges can be smaller.

In the measurement of liquid level, flow rate and density in the industrial process, if the measured medium has a high viscosity or corrosivity, it is usually isolated by means of air or liquid blowing. The flow of air and liquid blowing is often measured by float flow meter. In the case that the pressure of the gas (liquid) source fluctuates greatly or the pressure of the medium under test fluctuates greatly, in order to make the flow of the air and the liquid to be measured stably and accurately, some products match the float flow meter with the regulator (constant current device) into a set of constant differential pressure flow regulator

2. Differential pressure flow meter

The differential pressure flow meter consisting of a standard throttle device and a differential pressure type is limited in three aspects in small flow measurement.

The first limitation is the size of the pipe diameter. The standard throttle device is suitable for pipe diameters of 50mm and above. When the pipe diameter is too small, the diameter of the throttle device becomes correspondingly small, and it is difficult to perform similar processing according to the shape specified in the standard.

The second limitation is that the differential pressure is too small. This differential pressure is proportional to the square of the flow rate. When the flow rate is low to a certain value, the differential pressure becomes so small that it cannot be resolved.

The third limitation is the limit of the Reynolds number lower limit.The type of throttling device is different, and the lower limit of the Reynolds number is also different. In general, a Reynolds number ≥ 104 is a limit that can be used. The average flow rate and flow velocity corresponding to the lower limit of the Reynolds number is the lower measurement limit of the small flow rate.The Reynolds number is too small, and the outflow coefficient changes significantly with the change of Reynolds number, so that the uncertainty increases. 

Ⅰ.Product introduction

■ Gas measurement experts from the professional manufacturing technology industry

■Imported sensor with German patent technology

■Based on the principle of transverse power and transverse temperature difference, domestic exclusive production

Ⅱ.Product features

• Patented platinum RTD sensor with extremely high stability;
• Adopt proprietary technology “balanced structure package”, medium temperature self-compensation;
• Proprietary algorithms for high linearity, high repeatability, and high accuracy;
• The range ratio is 1000:1, which can be expanded according to user requirements;
• The pressure loss is small and negligible;
• Minimum flow rate can be measured down to zero with a resolution 0.001m/s;
• Large diameter and small flow measurement can be realized;
• Multi-point flow measurement is possible;
• The effects of vibration are negligible;
• The requirement of straight pipe section is not high:1-2D;
• Bidirectional measurement of medium flow;
• Independent of the temperature and pressure of the medium;
• Proprietary high temperature algorithm with medium temperature up to 510 °C;
• High humidity algorithm is adopted to achieve high precision measurement;
• Enter 12-point dynamic correction for flow signal, built-in 10-point correction;
• One button clear;
• Online dynamic correction current / voltage output;
• Wide screen LCD display,direct read instantaneous flow, cumulative flow;
• Not sensitive to small particles such as dust;
• On-line loading and unloading without stopping flow, easy maintenance;
• Corresponding product signals for different industries (flue gas, blast furnace gas, coke oven gas, car exhaust, etc).

Ⅲ.Product principle

The power plant flue gas flow meter is a flow meter based on the principle of thermal diffusion.That is, when the fluid flows through the heat generating object, the heat loss of the heat generating object is proportional to the flow rate of the fluid. Specifically, the flow meter's sensor has two standard-grade RTD, one for the heat source and one for measuring the temperature of the fluid. When the fluid flows, the temperature difference between the two is nonlinear with the magnitude of the flow, and the meter can convert this relationship into a linear output for measuring the flow signal.

There are two design methods for the flow meter manufactured by the principle of thermal diffusion: one is based on the principle of constant temperature difference; the other is based on the principle of constant power. Based on a common data model: P/ΔT=A+B(Q) N ---1. Here:P---dissipated power, ΔT---the temperature difference between the two sensors, A, B are the coefficients related to the thermal performance of the gas.

The principle of constant temperature difference: Δ T remains unchanged, and the dissipated power P is in a increasing relationship with the flow rate Q of the fluid.

Constant power principle: The dissipated power is constant, and the temperature difference Δ T is in a decreasing relationship with the flow rate Q of the fluid.

In the process of flue gas discharge,because of the complex working conditions of flue gas flow measurement,large dust, high temperature, water content, slurry, corrosion, large pipe diameter, the traditional measurement method is easy to plug, and based on differential pressure principle, in the case of low pressure, there is a measurement blind area. The GFM600 flue gas flow meter uses a proprietary flow data model and fuzzy theory to control temperature, humidity algorithm up to 510 °C, humidity up to 90%, and through two smooth probes (sensors) and proprietary scraping device to solve the above problems completely.

1. When commissioning, first open the upper guiding pipe valve, then slowly open the lower valve to allow the medium to enter the main leading tube smoothly (the medium should be prevented from hitting the float rapidly during operation, causing the float to fluctuate violently, affecting the display accuracy). Observe whether the magnetic red and white ball is turned over normally, then close the lower guiding pipe valve,open the drain valve,and let the liquid level in the main leading tube drop.According to this method, it is normal to operate three times,and then it can be put into operation (except for corrosive and other special liquids);

2. The main leading tube should be cleaned and impurities should be removed from time to time  according to the media conditions;

3. For liquid level gauges exceeding a certain length (common type > 3 m, anti-corrosion type > 2 m), it is necessary to add a fixed flange or ear climbing as a fixed support to increase the strength and overcome its own weight;

4. The installation position of the magnetic flapper level indicator should be avoided or away from the inlet and outlet of the material medium to avoid rapid changes in the local area of the material fluid and affect the accuracy of the liquid level measurement;

5. When equipped with remote transmission instruments, the following must be done:

The remote transmission instrument should be tightly attached to the  main leading tube of the liquid level gauge and fixed with stainless steel hoop (disabling iron);

The zero position of the remote transmission supporting instrument shall be on the same horizontal line as the zero position indication of the liquid level gauge;

The sensing surface on the remote transmission supporting instrument should be oriented and close to the main leading tube;

The connection between the remote transmission supporting instrument and the display instrument or the industrial computer is preferably laid by a protective tube alone or with a shielded two-core cable;

After the entrance hole of the junction box is laid, it is required to be well sealed so as to avoid the invasion of rainwater and moisture, which makes the remote transmission instruments unable to work properly.The junction box should be covered in time after overhaul or debugging.

Electromagnetic flow meters are commonly used flow meters in industrial measurement.Because of its wide application, customers often have problems in their use. Here we will talk about the solution to solve the problem of electromagnetic flow meters for measuring the liquid with large bubbles.Some customers mentioned why the electromagnetic flow meter is equipped with a lining, and we will answer this question from the principle of the electromagnetic flow meter.

In the process of measuring the liquid, there will be many bubbles in the electromagnetic flow meter, which will often lead to errors in the measurement of the flow meter, affecting the use.Generally, the fluid measured by the electromagnetic flow meter will contain some bubbles, and if these bubbles are evenly distributed, it will not affect the measurement, but once the bubble becomes larger,the whole electrode can be covered when passing the electrode, so that the input loop of flow signal is opened instantaneously, causing the output signal to shake.

How to determine the measurement error of electromagnetic flow meter is caused by bubbles contained in the measured liquid?How to deal with this situation? Let's briefly introduce it.

When the measurement result is shaken, the excitation loop current of the magnetic field is cut off immediately. If the meter still displays and is unstable at this time, it is mostly caused by the influence of the bubble.

After determining a large number of bubbles affecting the measurement results of the electromagnetic flow meter, it is necessary to find a relevant solution. If it is judged that a large amount of air bubbles are mixed into the liquid caused by the installation position, such as the electromagnetic flow meter is installed at the high point of the pipeline and the gas is stored or the external air is inhaled to cause the flow meter to shake, replacing the installation position is the most effective solution,but many applications are large diameter or the installation position is not easy to change. It is recommended to install a gas collecting bag and an exhaust valve upstream of the electromagnetic flow meter to eliminate excess gas, reduce the influence factors on the measurement results, and ensure accurate measurement.

Why should the electromagnetic flow meter need lining,this should start from the principle of electromagnetic flow meter.Electromagnetic flow meters generally have a set of coils and two electrodes.The function of the coil is to add an electric field to the fluid. The flowing conductive liquid is equivalent to a conductor. According to Faraday's law of electromagnetic induction,  when the conductor cuts the magnetic field line, it will produce an electromotive force proportional to the speed. The role of the electrode is to measure this induced electromotive force, so only the electrode in the measuring tube is connected to the conductive liquid, and the other part is the inner lining,to ensure insulation, electromagnetic flow meter can work normally. If the metal pipe with a magnetic field is also in contact with the liquid, a short circuit between the conductive liquid measured by the electromagnetic flow meter and the metal tube , there will be conduction,and the electric potential will be led away so that the electromagnetic flow meter cannot measure the electric potential.So the inside of the electromagnetic flow meter is lined.

When measuring the flow rate, the conductive liquid flows at a velocity V through a magnetic field perpendicular to the flow direction. The flow of the conductive liquid induces a voltage proportional to the average flow velocity.Its induced voltage signal is detected by two or more electrodes that are in direct contact with the liquid and sent to the converter through the cable for intelligent processing, and then the LCD displays or converts the 4-20ma standard signal and 0-1khz output.In this way, the electromagnetic flow meter can measure the flow of the conductive fluid. The electromagnetic flow meter can only measure the flow of conductive liquid, so there must be a lining inside.