Blog posts of '2018' 'October'

Throttling devices

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.

Application of flow meter in micro - flow measurement

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. 

Flue gas flow meter

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.

Operation guide for magnetic flapper level indicator

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.

How to solve the electromagnetic flow meter to measure liquid with large bubbles?

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.

What are the advantages and disadvantages of metal tube float flow meter?

The metal tube float flow meter is a variable area flow measuring instrument commonly used in industrial automation process control. It has the characteristics of small size, large detection range and convenient use. It can be used to measure the flow of liquids, gases and vapors, and is especially suitable for medium flow measurement with low flow rates and small flows. What are the advantages of metal tube float flow meter products?

1. High temperature resistance, high pressure resistance and corrosion resistance

The ability to measure high temperature, high pressure fluids is a major advantage of metal float flow meters, which measure liquid and gas flows up to 400℃and pressures up to 70 MPa. In this case,  the floating position can not be observed with the human eye, but the flow rate can be indicated by the magnetic coupling induction display system. The flow meter itself is often made of high quality stainless steel, some lined with engineering plastics to measure corrosive fluids.

2. Wide range of applications

Flexible design according to flow process parameters. For example, at low temperatures, if the medium tends to crystallize and solidify. Or to prevent the low temperature fluid from absorbing heat from the outside. Or when the fluid in the pipeline passes through the instrument at a temperature higher than room temperature, due to the temperature drop, the float does not work properly, the fluid viscosity has a significant change affecting the measurement of special needs,Or the fluid viscosity has a significant change affecting the special needs of the measurement, the flow meter with jacket insulation design can be used; the flow pulsation is large, and the flow meter with damping measures can be selected; the jacketed heat preservation flow meter can vacuum the interlayer to achieve the purpose of heating and heat preservation; when measuring high temperature fluid. A heat sink is designed in front of the indicator.

3. Flexible interface

The metal tube float flow meter can conveniently meet the installation conditions of the field pipeline.The inlet and outlet of the metal tube float flow meter can be designed with the structure of vertical inflow and horizontal outflow, vertical inflow and vertical outflow, horizontal inflow and outflow, and horizontal inflow and horizontal flow with different heights.

4. Remote measurement and control, intelligent operation

The metal float flow meter has no auxiliary power supply in the measurement field in many cases, and the pointer display flow does not need to be driven by an external power supply. Usually, the display has a modular remote analog signal output interface (4 mA to 20 mA). More advanced is also equipped with a digital interface compatible with the HART communication protocol, which can be used to calibrate and test the linearity of the transmitter by manual operation or PC programming, or to perform on-site parameter tuning and computer integration to implement remote measurement and control.

Disadvantages of metal tube float flow meters:

1. When the fluid is used and the factory calibration fluid is different, the flow indication value correction is required. The rota meter for liquids is usually calibrated with water, and the gas is calibrated with air. If the actual density and viscosity of the fluid are different, the flow rate deviates from the original index value and is corrected for conversion.

2. The glass rotator flow meter has the risk of fragile glass tubes, especially for non-guided structure floats for gas.

3. Most structural float flow meters can only be used for pipeline installations from bottom to top vertical flow.

4. Rotor flow meter application is limited to small and medium diameter pipe. Ordinary full flow type rotary flow meter cannot be used for large diameter. Glass tube rotor flow meter has maximum diameter of 150mm, metal rotor flow meter is 200mm, and larger diameter can only be used with diverting flow instrument.

How to select sensors reasonably?

Modern sensors vary widely in principle and structure. How to select   sensors  reasonably according to specific measurement purposes, measurement objects and measurement environment is the first problem to be solved when measuring a certain quantity. When the sensor is determined, the matching measurement method and measuring device can be determined. The success or failure of the measurement results largely depends on whether the sensor's selection is reasonable.

1. Determine the type of sensor according to the measured object and measurement environment

To carry out a specific measurement work, we must first consider the principle of the sensor,which needs to be determined after analyzing various factors.Because, even if measuring the same physical quantity, there are also many kinds of sensors to choose, which principle of sensor is more suitable, then we need to consider the following specific problems according to the characteristics of the measured quantity and the use conditions of the sensor: the size of the measurement range; the requirements of the measured position on the volume of the sensor; the measurement method is Contact or non-contact; signal extraction method, wired or non-contact measurement; the source of the sensor, domestic or imported,  the price can withstand or not,or self-developed.

After considering the above issues, you can determine which type of sensor to use and then consider the specific performance of the sensor.

2. Sensitivity selection

Generally, in the linear range of the sensor, the higher the sensitivity of the sensor is, the better. Because only the sensitivity is high, the value of the output signal corresponding to the measured change is relatively large, which is beneficial to signal processing.However, it should be noted that the sensitivity of the sensor is high, and the external noise that is not related to the measurement is easily mixed in, and is amplified by the amplification system, which affects the measurement accuracy. Therefore, the sensor itself should be required to have a high signal-to-noise ratio, and the interference signal introduced from the outside is reduced.

The sensitivity of the sensor is directional. When the measurement is a single vector and its directivity requirements are high, other sensors with small sensitivity should be selected; if the measurement is a multi-dimensional vector, the cross sensitivity of the sensor is required to be as small as possible.

3. Frequency response characteristics

The frequency response characteristics of the sensor determine the frequency range to be measured.The measurement conditions must be kept undistorted within the allowable frequency range. In fact, the response of the sensor always has a certain delay, and the shorter the delay time, the better. The frequency response of the sensor is high, the measurable signal frequency range is wide. Due to the structural characteristics, the inertia of the mechanical system is large, and the frequency of the measurable signal is low because of the sensor with low frequency.

In dynamic measurement, the response characteristics should be based on the characteristics of the signal (steady state, transient, random, etc.) to avoid excessive error.

4. Linear range

The linear range of the sensor is the range in which the output is proportional to the input. In theory, within this range, the sensitivity remains constant. The wider the linear range of the sensor, the larger the range and the guaranteed measurement accuracy. When selecting a sensor, when the type of sensor is determined, it is first necessary to see if its range meets the requirements. But in reality, any sensor can't guarantee absolute linearity, and its linearity is relative. When the required measurement accuracy is relatively low, within a certain range, the sensor with less nonlinear error can be approximated as linear, which will bring great convenience to the measurement.

5. Stability

The ability of a sensor to remain unchanged after a period of use is called stability. In addition to the structure of the sensor itself, the factors affecting the long-term stability of the sensor are mainly the use environment of the sensor. Therefore, in order to make the sensor have good stability, the sensor must have strong environmental adaptability.

Before selecting a sensor, investigate the environment in which it is used, select the appropriate sensor according to the specific use environment, or take appropriate measures to reduce the environmental impact. The stability of the sensor has a quantitative index, and it should be calibrated again before use to determine whether the performance of the sensor has changed.In some cases where the sensor is required to be used for a long period of time and cannot be easily replaced or calibrated, the selected sensor has stricter stability requirements and can withstand the test for a long time.


Accuracy is an important performance index of sensor, it is an important link related to the measurement accuracy of the whole measurement system.The higher the accuracy of the sensor, the more expensive it is. Therefore, the accuracy of the sensor can be as long as   meets the accuracy requirements of the entire measurement system, and it is not necessary to select too high. This makes it possible to select a cheaper and simpler sensor among the many sensors that meet the same measurement purpose.

If the purpose of the measurement is qualitative analysis, with high repetition accuracy can be selected.but the sensor with high absolute value accuracy is not suitable. If it is for quantitative analysis, it is necessary to obtain precise measurement values, it is necessary to select a sensor with an accuracy class that meets the requirements.For some special applications, if you can't choose the right sensor, you need to design and manufacture the sensor yourself.The performance of the home-made sensor should meet the requirements for use.

Principle and purchase on selection of magnetic flapper level indicator

Principle of magnetic flapper level indicator

The magnetic flapper level indicator is mounted on the outside or above the tank to indicate and control the seal type in the tank.The drain valve  and the connecting flange can be installed as needed.The indicator is composed of magnetic color plates. When the magnetic float ball in the main pipe flips with the liquid level rising, the liquid level can be displayed. A magnetic switch or a remote transmitter can also be installed on the main pipe to output switch signals or analog signals. It is suitable for high temperature, high pressure, corrosion resistant and other occasions.Local display and remote control.The main pipe adopts seamless steel pipe, and the connecting pipe is welded by a pull hole, and the inside is free from scratches.The mounting method can be side-mounted and top-mounted, and the lower end of the body is sealed.

Purchase on selection of magnetic flapper level indicator

Magnetic flapper level indicator is also called magnetic level gauge, magnetic column level gauge,magnetic float level gauge. It works on the principle of magnetic coupling. The product makes up for the multiple shortcomings of glass tube level gauge which can not work under high temperature and high pressure and is fragile.

Magnetic flapper level indicator has two mounting methods: side mount and top mount. No matter which way, the remote transmission device can be bundled, so that the liquid level gauge can display the liquid level on site and remotely monitor the liquid level. The magnetic flapper level indicator can be called a remote transmission type magnetic flapper level indicator.

Although the process of making a magnetic flapper level indicator is very simple, but the magnetic flapper level indicator as measuring instrument, especially remote transmission type magnetic flapper level indicator.It is difficult to guarantee the quality of the products without a production license if they are not examined by the Quality Supervision Bureau.Therefore, it is necessary to choose a manufacturer with a production license and good reputation for purchasing the magnetic flapper level indicator.The price may be slightly higher, but the quality of the product is guaranteed and the after-sales service is guaranteed.

Difference between vacuum gauge and ordinary pressure gauge

In fact, the vacuum gauge is a kind of pressure gauge.

There are several kinds of work principles.

Classification by vacuum gauge measurement principle

Directly measured vacuum gauge, which directly measures the force per unit area, has:

(1) Static liquid level vacuum gauge: The pressure is measured by the liquid level difference at both ends of the U-shaped tube.

(2) Elastic element vacuum gauge:The surface of the container connected to the vacuum is subjected to pressure to generate elastic deformation to measure the magnitude of the pressure value.

Indirectly measured vacuum gauge, when the pressure is 10-1 Pa, the force acting on the surface of 1 cm 2 is only 10-5 N, and it is obviously difficult to measure such a small force. However, the change in pressure can be measured indirectly based on changes in physical quantities associated with gas pressure at low pressure. Vacuum gauges belonging to this category are:

(1) Compressed vacuum gauge: The principle is to apply Boyle's law on the basis of the U-tube, that is,a certain amount of gas to be tested  is subjected to isothermal compression to increase the pressure,  so as to be measured by a U-tube vacuum gauge. Then calculate the measured pressure using the relationship between volume and pressure.

(2) Heat conduction vacuum gauge: It is made by the principle that the heat conduction of gas under low pressure is related to pressure. Commonly used are resistance vacuum gauges and thermocouple vacuum gauges.

(3) Thermal radiation vacuum gauge: The principle of thermal radiation of gas under low pressure is related to pressure.

(4) Ionization vacuum gauge: The principle that the gas molecules are impacted and ionized by the charged particles under low pressure,and the generated ion current changes with the electric power.Such as: hot cathode ionization vacuum gauge, cold cathode ionization vacuum gauge and radioactive ionization vacuum gauge.

(5) Discharge tube indicators:The degree of vacuum is determined by the nature of the gas discharge condition and the discharge color are related to pressure, generally only as a qualitative measurement.

(6) Viscous vacuum gauge: The principle of external friction is used to exchange the momentum of the gas and the vessel wall under low pressure. Such as diaphragm vacuum gauge and magnetic suspension rotor vacuum gauge.

(7) Field-induced microscopy:The pressure is calculated by the relationship between adsorption and desorption time and pressure.

(8) Partial pressure vacuum gauge: The mass spectrometry technique is used to measure the partial pressure of the mixed gas. Commonly used are quadrupole mass spectrometers, cyclotron mass spectrometers, and radio frequency mass spectrometers.

Vacuum gauges are generally used for negative pressure. Compared with ordinary pressure gauges, it is only the difference between the range of pneumatic pressure and the accuracy.

The measurement range of the vacuum pressure gauge is 0-1 atmosphere, and the ordinary pressure gauge is usually an amount of atmospheric pressure of 0-tens, several hundred or even more. The measured readings will be much more accurate when the range is selected.

Principle and characteristics of radar level meter

1. Measuring principle of radar level meter

The radar liquid level meter adopts the operating mode of transmitting -reflection-receiving.The antenna of the radar level meter emits electromagnetic waves,which are reflected by the surface of the measured object and then received by the antenna.The time from transmitting to receiving of electromagnetic waves is proportional to the distance to the liquid surface.The formula is as follows: D=CT/2

In the formula, D——the distance from the radar level meter to the liquid level; C——the speed of light; T—— the running time of electromagnetic waves.

Radar level meter records the duration time of pulse wave,and the transmission speed of electromagnetic wave is constant, then the distance from the liquid surface to the radar antenna can be calculated to know the liquid level of the liquid surface.  

In practice, there are two ways for radar level meters,namely, frequency-modulated continuous wave and pulse wave.The liquid level meter adopting the frequency-modulated continuous wave technology has large power consumption and must adopt a four-wire system, and the electronic circuit is complicated.The liquid level meter using radar pulse wave technology has low power consumption and can be powered by two-wire system 24V DC, which is easy to achieve intrinsic safety, high accuracy and wider application range.The VEGAPULS radar level meter uses pulsed microwave technology.Its antenna system emits a pulse beam with a frequency of 6.3 GHz and a duration time of 0.8 ns,and then pauses for 278 ns.During the pause period of the pulse transmission,the antenna system will act as a receiver,receive the reflected wave, and simultaneously perform echo image data processing to give the indication and the electric signal.

2. Characteristics of radar level meter

(1) Radar level meter adopts integrated design ,without movable parts,no mechanical wear, long service life.

(2) The electromagnetic wave emitted by the radar level meter can pass through the vacuum without any transmission medium, and has the characteristics of being free from the influence of the atmosphere, steam and volatile fog in the tank, and can be used for the liquid level measurement of the volatile medium,such as crude benzene.

(3) The radar level meter can be used for liquid level measurement of almost all liquids.When the electromagnetic wave is reflected on the surface of the liquid level, the signal will attenuate.When the signal attenuates too much,the radar level meter can not detect enough electromagnetic wave signal. Conducting medium can reflect electromagnetic wave well.For the VEGAPULS radar level meter, even micro-conducting substances can reflect enough electromagnetic waves.Non-conductive media with dielectric constant greater than 1.5 (the dielectric constant of air is 1.0) can also ensure sufficient reflected waves,and the larger the dielectric constant, the stronger the reflected signal. In practical,almost all media can reflect enough reflected waves.   

(4) Non-contact measurement is adopted, which is not affected by physical properties such as density and concentration of liquid in the tank.

(5) The measuring range is large, and the largest measuring range is 0~35m,which can be used for liquid level measurement of high temperature and high pressure.

(6) The antenna and other key components are made of high-quality materials, which have strong corrosion resistance and can adapt to a strong corrosive environment.

(7) Rich in functions,with a false wave learning function. Enter the actual liquid level of the liquid level,the software can automatically identify the false echo from the liquid level to the antenna,and eliminate the interference of these waves.

(8) The parameter setting is convenient,and can be set by the simple operation key on the liquid level meter.It can also be set remotely or directly to the communication end of the level meter by using the HART protocol operator or a PC equipped with VEGA Visual Operating software.