是差压流量计的一个品种，它在工业上的开发应用已有数十年的历史。 Target type flowmeter is a variety of differential pressure flowmeter, which has been developed and applied in industry for decades. In the 1970s, China developed electric and pneumatic target type flow transmitters. It is a testing instrument for electric and pneumatic unit combination meters. Since the force converter directly used the force balance mechanism of the differential pressure transmitter at the time, this flowmeter inevitably brought many defects caused by the force balance mechanism itself, such as easy zero drift, low measurement accuracy, and reliable lever mechanism. Poor sex, etc. Due to the drag of the poor performance of the force balancing mechanism, many advantages of the target type flowmeter itself have not been effectively used. So far, users' bad impressions of the old target flowmeter have not been eliminated.
The force converter of the target type flowmeter uses a strain type force converter, which completely eliminates the shortcomings of the above-mentioned force balancing mechanism. The new target type flowmeter also applies microelectronic technology and computer technology to the signal converter and display part. Has a series of advantages, I believe it will play an important role in many flowmeters in the future.
原理和结构 Principle and structure of target flowmeter
1. Working principle The schematic diagram of the target flow meter. A circular target plate is placed coaxially in the center of the measuring tube (instrument meter body). When the fluid hits the target plate, a force F is applied to the target plate, which is between the flow velocity V, the medium density ρ, and the target area A. The relational formula is shown in formula (1). (1) where F——force on the target, N; CD——resistance coefficient; ρ——fluid density, kg / m3; V——fluid flow velocity, m / s; A——force on the target Area, m2. After derivation and conversion, the flow calculation formula is as follows: where qm, qv——respectively are mass flow and volume flow, kg / h, m3 / h; α——flow coefficient; D——inner diameter of the measuring tube, mm; β ——Diameter ratio, β = d / D; d——diameter of target plate, mm. The remaining symbols are the same as above. The target board is transformed into an electric signal by a force converter, and after pre-amplification, AD conversion and computer processing, the corresponding flow and total amount can be obtained. As shown in Figure 1. Figure 2 Simplified structure of target type flowmeter 2. Structure The structure of the target type flowmeter is shown in Figure 2. It consists of detection device, force converter, signal processing and display instrument. The detection device includes a measuring tube and a target plate, the force converter is a strain gauge sensor, and the signal processing and display instrument can be directly read and displayed in situ or can transmit standard signals at long distances. The structure type of the target type flowmeter can be divided into pipeline type, clamp type and plug-in type, etc., and various types of structure types can also be divided into two types: integrated and separated. The integrated type is a direct reading display on the site, while the separate type separates the digital display from the detection device (generally no more than 100m).
流量计主要特点 Third, the main characteristics of target flowmeter
1. The sensing element has no moving parts, and its structure is simple and firm; 2. The application range and adaptability are very wide. The fluid medium in general industrial processes, including liquid, gas and steam, caliber range (above DN15), various tasks The state (high, low temperature, normal pressure, high pressure) can be applied. It can be said that its application range is more beautiful than that of the orifice flow meter. 3. High accuracy, total measurement can reach 0.2% R; 4. Wide range, 4: 1 ～ 15: 1 to 30: 1; 5. It can solve difficult flow measurement problems, such as measurement containing impurities (particles) Dirty fluids such as crude oil, sewage, high temperature residue, slurry, caustic soda, asphalt, etc .; 6. High sensitivity, can measure small flow rate, flow rate can be as low as 0.08m / s; 7, for small diameter (DN15 ~ DN50), low Reynolds number (Red = 103 ~ 5 × 103) fluid, it can make up for occasions where standard throttling devices are difficult to apply, such as small caliber steam flow measurement, etc .; 8. It can adapt to the measurement of high parameter fluids, pressure Up to dozens of MPa, temperature up to 450 ℃; 9, can be used for the measurement of bidirectional flowing fluid; 10, low pressure loss, about half of the standard orifice plate; 11, strong anti-interference ability of upstream choke pieces, straight upstream pipe section The length is generally 5 ～ 10D. 12. Dry (hanging weight) calibration can be adopted to bring convenience to the user's periodic calibration. 13. Direct-reading meters do not require external energy, are clear, easy to operate, and can be output. Standard signal (pulse frequency or current signal);
14. The meter has a high performance-price ratio and is an economical and affordable flow meter; 15. It is simple and convenient to install and easy to maintain.
The target flowmeter summarized by everyone hopes that it will be helpful to everyone.
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