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Introduction
Divided into two categories: one type is contact type, including single flange static pressure / double flange differential pressure level transmitter, float type liquid level transmitter, magnetic liquid level transmitter, input liquid level change Feeder, electric inner float level transmitter, electric float level transmitter, capacitive level transmitter, magnetostrictive level transmitter, servo level transmitter, etc. The second type is non-contact type, which is divided into ultrasonic liquid level transmitter and radar liquid level transmitter.
Static pressure input type liquid level transmitter (level gauge) is suitable for liquid level measurement of various media in petrochemical, metallurgy, electric power, pharmaceutical, water supply and drainage, environmental protection and other systems and industries. The compact structure, simple adjustment and flexible installation make it easy for users to use. Standard signal output methods such as 4 to 20 mA, 0 to 5 v, and 0 to 10 mA are optional by the user as needed.
Measuring the liquid level using the hydrostatic principle is an important application of pressure sensors. The special intermediate cable with ventilation duct and special sealing technology not only ensure the watertightness of the sensor, but also make the reference pressure chamber communicate with the ambient pressure, thus ensuring high precision and high stability of the measurement.
Comparison of different liquid level sensors
1. Float type liquid level sensor
The float type liquid level transmitter changes the magnetic float to the float, and the liquid level sensor is designed according to the Archimedes buoyancy principle. The float type liquid level transmitter uses a small metal film strain sensing technology to measure the liquid level, boundary or density of the liquid. It can be used for routine setting operations by field buttons during operation.
2, float type liquid level sensor
The float type liquid level transmitter is composed of a magnetic float ball, a measuring pipe, a signal unit, an electronic unit, a junction box and a mounting member. Generally, the magnetic float has a specific gravity of less than 0.5, and can float above the liquid surface and along the measuring pipe. Moving, the measuring tube is equipped with a measuring component, which can convert the measured liquid level signal into a resistance signal proportional to the liquid level change under the action of external magnetic field, and convert the electronic unit into 4-20 mA or other standard signal output.
The liquid level sensor is a module circuit, which has the advantages of acid resistance, moisture resistance, shock resistance, corrosion resistance, etc. The circuit contains a constant current feedback circuit and an internal protection circuit, so that the maximum output current does not exceed 28 mA, thus reliably protecting the power supply and making the power The meter is not damaged.
3. Static pressure level sensor
The transmitter works by the measurement principle of hydrostatic pressure. It generally uses a silicon pressure load cell sensor to convert the measured pressure into an electrical signal, and then is amplified by an amplifier circuit and compensated by a circuit, and finally 4 to 20 mA or 0 to 10 mA. Current mode output.
working principle
The principle of static pressure measurement: When the liquid level transmitter is put into a certain depth in the liquid to be measured, the pressure formula of the liquid surface of the sensor is: Ρ = Ï .gH + Po:
P : the pressure on the liquid surface of the transmitter
Ï: measured liquid density
g : local gravity acceleration
Po : atmospheric pressure on the liquid surface
H : Depth of the transmitter into the liquid
At the same time, the pressure of the liquid is introduced into the positive pressure chamber of the sensor through the gas-conducting stainless steel, and the atmospheric pressure Po on the liquid surface is connected with the negative pressure chamber of the sensor to offset the Po on the back of the sensor.
The pressure measured by the sensor is: Ï .gH , and obviously, by measuring the pressure P, the liquid level depth can be obtained.
Features:
◆Good stability, long-term stability of fullness and zero can reach 0.1%FS/year. In the temperature range of 0 to 70 °C, the temperature drift is less than 0.1% FS and is less than 0.3% FS over the entire allowable operating temperature range.
â—† With reverse protection and current limiting protection circuit, the positive and negative poles will not damage the transmitter during installation, and the transmitter will automatically limit the current to within 35MA.
â—† Solid structure, no moving parts, high reliability and long service life.
â—† Easy installation, simple structure, economical and durable.
The main technical parameters:
Process: Diffused silicon ceramic capacitor sapphire capacitors are optional. Split-type integrated option, range: 0---0.5---200 meters, output: 4---20mA (2-wire system) Power supply: 7.5---36VDC Recommended 24VDCCBM-2100/CBM-2700 input static The pressure gauge is a reliable anti-corrosion probe with a ceramic measuring unit for level measurement of clean water, sewage and salt water. The GY500 is divided into a split-type liquid level transmitter with a diffused silicon piezoresistive core, 316 stainless steel structure, and the shell is isolated and explosion-proof. The input level gauge is mainly suitable for rivers, groundwater levels, reservoirs, water towers and containers. Level measurement and control. The circuit adopts signal isolation amplification, cut-off interference design (strong anti-interference ability, lightning protection) over-voltage protection, current limiting protection, anti-shock, anti-corrosion design. Main technical parameters: b] Measurement medium: Types of liquid pressure such as water and oil: gauge pressure, absolute pressure (no default gauge pressure required)
b] Range: 0～300m intermediate range Optional comprehensive precision: 0.1%FS Output signal: 4～20mA (two-wire system), 0～5V, 1～5V, 0～10V (three-wire system) Supply voltage: 12～36VDC medium Temperature: -30～60°C Ambient temperature: -40～85°C Zero point temperature drift: ≤±0.05%FS°C Range temperature drift: ≤±0.05%FS°C Compensation temperature: 0~70°C Safety overload: 150%FS limit overload : 200% FS sampling frequency: ≤ 2ms Load capacity: (current type) 250~1425Ω (voltage type) ≥ 2KΩ Sealing level: IP68 Long-term stability performance: 0.1% FS / annual vibration effect: Within the mechanical vibration frequency 20Hz ~ 1000Hz, Output change is less than 0.1% FS Mechanical connection (threaded interface): Input type (submersible)] Product size (mm): b]
Input split type liquid level transmitter
⊙Using high-precision, isolated sensitive components imported from the United States, reliable performance
⊙ gauge or absolute pressure measurement
⊙ Measuring range width: 1mH2O ~ 200mH2O
⊙ Output: 4~20mA or 0~5V
⊙Power supply voltage: 24VDC (12～36VDC), mV output type is constant current 1.5mADC or constant voltage 12VDC power supply
⊙ High precision, better than 0.2% FS
⊙100% waterproof and moisture proof, protection class IP68
⊙Complete circuit function, easy to adjust
Product parameters
Measured medium: liquid (weakly corrosive)
Pressure type: gauge pressure
Range: 0～0.1M～1M～3M～5M～10M～20M～50M～100M～200M～500M (water level high/depth, minimum range is 0.1m)
Output: 4 to 20 mA (two-wire system), 0 to 5 VDC, 0 to 10 VDC, 0.5 to 4.5 VDC (three-wire system)
Comprehensive accuracy: ±0.25% FS, ±0.5% FS
Power supply: 24V Dc (9 ~ 36VDC)
Insulation resistance: ≥1000 MΩ/100VDC
Load resistance: Current output type: up to 800Ω
Voltage output type: greater than 50KΩ
Medium temperature: -20 ~ 85 ° C
Ambient temperature: -20 ~ 85 ° C
Storage temperature: -40 to 90 ° C
Relative humidity: 0～95% RH
Sealing level: IP68
Overload capability: 150% FS
Response time: ≤5mS
Stability: ≤±0.15%FS/year
Vibration effect: ≤±0.15%FS/year (mechanical vibration frequency 20Hz～1000Hz)
Electrical connection: 3/5 core air-shielded cable is fully sealed; standard wiring 8 meters
Pressure connection: input type
Connecting thread material: 304/316L stainless steel
Similar difference
The liquid level switch is a controller that keeps the water level constant according to the signal output of the liquid level sensor to open the valve for discharging water or water. It can also be said that the liquid level switch outputs a kind of switching signal. The liquid level switch first determines the height of the liquid level, and outputs the switching quantity signal according to the height. The liquid level sensor outputs a form in which the height of the liquid level is converted into an electrical signal. We can process the electrical signal, such as the plc, data collector or professional display to output the level of the liquid level. There is also the same principle of the liquid level switch and the liquid level sensor. However, the liquid level switch is a switch control circuit, and the liquid level sensor is a circuit component equivalent to a transformer and a converter.
Photoelectric level sensor
The photoelectric liquid level sensor is a new type of contact point liquid level measurement and control device developed by utilizing the principle of reflection and refraction of light at two different medium interfaces. The utility model has the advantages of simple structure, high positioning precision, no mechanical parts, no need for debugging, high sensitivity and corrosion resistance, low power consumption, small volume and the like, and is gradually recognized by the market.
1. Since the output of the liquid level is only related to whether the photoelectric probe is in contact with the liquid surface, and is independent of other characteristics of the medium, such as temperature, pressure, density, electricity, etc., the photoelectric liquid level sensor has accurate detection and high repeatability; the response speed is fast. The liquid level control is very precise and can be installed directly without adjustment.
2. Since the photoelectric liquid level sensor probe is relatively small in size, it can be installed separately in a small space for use in a special tank or container. In addition, a plurality of photoelectric probes can be mounted on one measuring body to form a multi-point liquid level sensor and a variable controller.
3. Since all the components inside the sensor are resin-sealed, there is no mechanical moving parts inside the sensor, so the photoelectric liquid level sensor has high reliability, long life and maintenance-free.
Industry status
At the beginning of the 21st century, there is still no small challenge in the industrialization of liquid level sensors. It is reported that there are more than 1,700 enterprises engaged in the production and research and development of liquid level sensors in China. The annual output of liquid level sensors has exceeded 2.4 billion, and the liquid level sensor products have reached 10 categories, 42 categories and more than 6,000 varieties, showing good results. The development trend, but in this enterprise, foreign-funded enterprises have obvious advantages, and the proportion of foreign-funded enterprises reaches 67%, especially in Japan, the United States, South Korea and Germany, and the proportion of state-owned enterprises and national enterprises is only 33%. The comprehensive strength of domestic and foreign enterprises is very small, the scale is small, the talent shortage, the research and development ability is weak, and it is difficult to compete with foreign enterprises.
More importantly, technically, the domestic liquid level sensor technology is weak, mainly in the following three points:
First, the core technology and basic capabilities are lacking. The core chips are heavily dependent on foreign imports. Domestic enterprises have significant gaps with foreign companies in high-end, high-sensitivity analysis, component analysis and high-end applications.
Second, in the aspects of design, reliability, packaging, etc., lack of unified standards and independent intellectual property rights, no breakthroughs have been made in interfaces, deep etching, high temperature ohmic contact, high reliability MEMS packaging, rapid testing, high simulation and other technologies. Industrialization verification;
Third, the products are not comprehensive enough in terms of varieties, specifications, series, etc. There are still no small differences in measurement accuracy, temperature characteristics, response time, stability, reliability and other technical indicators. Therefore, China's float level sensor companies have a long way to go.
Prospects
In recent years, the domestic magnetic flap liquid level sensor market has continued to grow, with a speed of more than 10%. In 2010, China's liquid level sensor sales reached 90.5 billion yuan. It is predicted that China's liquid level sensor market will develop steadily and rapidly in the next five years. Under the driving force of the substantial growth of the Internet of Things market, the market size of China's liquid level sensor is expected to reach 1.2 billion yuan in 2015.
According to statistics, by 2013, the overall market size of China's Internet of Things will reach 750 billion yuan. As the bottom and most basic links of the "pyramid" of the Internet of Things, the liquid level sensor industry will directly benefit from it.
liquid level sensor
The level sensor (static pressure level gauge / level transmitter / level sensor / water level sensor) is a pressure sensor that measures the liquid level. The static pressure input type liquid level transmitter (level gauge) is based on the principle that the measured hydrostatic pressure is proportional to the height of the liquid. It adopts foreign advanced isolated diffusion silicon sensitive components or ceramic capacitor pressure sensitive sensors, which will be static. The voltage is converted into an electrical signal, which is then converted into a standard electrical signal (typically 4 to 20 mA / 1 to 5 VDC) by temperature compensation and linear correction.