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technical article
The glass rotor flowmeter is explosive and the cover is removed. The cover is used for protection.
2012-3-15 14:37:03

使用及维护的一些小建议,供大家参考: Glass Rotameter The following are some suggestions for the use and maintenance of glass rotameter for your reference:
1. When you get the glass rotor flowmeter, first observe whether the glass tube in the glass rotor flowmeter is intact, because the glass tube is easily damaged. The second is to remove the fixed object, and gently tilt it to see if the rotor can slide up and down freely. If you cannot slide freely, you need to gently vibrate the support plate so that it can generally slide. If you can no longer slide, you need to ask a professional technician to disassemble the machine. 2. When installing to the pipeline, firstly check whether the upstream and downstream pipelines are in a straight line. If it is not on a straight line, it will not only affect the measurement accuracy of the meter, but also damage the meter. 3. The first two points must be correct before they can be used. The operator should read the manual in detail before using it. When opening the valve, you must open it slowly. If it is estimated that the flow can float the rotor and the rotor does not move upwards, immediately stop and continue to open the valve at the same time, and gently tap the pipe to make the rotor slowly rise. Many operators have opened the valve too fast and just installed new equipment. The sudden opening of the valve caused damage to the glass tube in the glass rotor flowmeter. This should be brought to the attention of the user. 4, safe use, some operators like to remove the front cover, this is not allowed, because the glass tube is easy to burst, remove the cover, the cover plays a protective role. Therefore, you cannot remove the cover and use it. 5. It should be kept warm during winter use. If it is not used at night, the residual liquid in the flow meter must be discharged, so as not to freeze the glass tube.


How to choose glass rotor flowmeter correctly Glass rotor flowmeter is a kind of instantaneous flow measuring instrument which is simple to use, convenient to read and very versatile. In the field of environmental protection equipment and instruments, the amount is more than 30,000 units / year. Therefore, it is extremely important to choose and use this instrument.
I. Variety and selection of glass to flowmeter
The glass rotor flowmeter can be divided into eight types: ordinary type, ribbed vascular type, micro flow and small outline type, corrosion resistance, laboratory type, thermal insulation type, alarm type and high pressure resistance type according to its use and applicable range. series. According to the national series of instrument series spectrum, no matter which series includes a maximum of 12 calibers from 1mm to 100mm, the measurable flow range is: liquid (water) 0.1ml / min ~ 40m3 / hour, gas (Air) 1ml / min ~ 1000m3 / hour. The glass rotor flowmeter used for environmental protection instruments generally has a diameter of no more than 10 mm, and the measured flow belongs to a small flow range.
The selection of glass rotor flowmeter can be considered from the following aspects.
1. The object of measurement. That is to measure the type of medium, pressure, and chemical properties. For liquid and gaseous media, for corrosive media, a corrosion-resistant flowmeter should be selected. 2. The performance of the flow meter itself. After the above conditions are determined, generally speaking, if there is no major change in price, the needle valve is preferred to be placed on the upper part of the flowmeter; those with larger flow holes are directly flow-scaled; simple structures; smaller external dimensions, etc . If it is a small flow range, you can use the ball float type, because it is stable during measurement, not easy to accumulate dust, high accuracy, and good interchangeability. 3. Select based on price. Generally speaking, high accuracy and high price. To select the accuracy level of the instrument according to the measurement purpose, if you only need to control the throughput of the measurement medium and adjust it after trial operation, you must always stabilize the throughput in the future, then the accuracy is secondary.
的刻度修正 Calibration of glass tube rotor flowmeter
The calibration of the glass rotor flowmeter is obtained by the factory under the conditions of the factory using water and dry air close to the ideal fluid as the medium. However, there are two situations where the scale value of the flowmeter cannot be used directly: one is that the measurement medium is not water and air, and the other is that the medium is water and air, but its state (temperature, pressure) and scale The status is different. In this way, when using a flow meter, in order to obtain a correct measurement result, a problem arises that the scale value needs to be corrected. Therefore, solving the calibration of the glass rotor flowmeter is the key to using this instrument. Considering that environmental protection instruments use rotor flowmeters to measure the flow of gaseous media, only the density correction in gaseous media measurement is discussed below. Because the viscosity of the gaseous medium is small, the viscosity effect is omitted in the discussion. Practice has proved that this does not affect the accuracy after the correction.
The following is the general expression of the flowmeter of the rotor flow meter (1) is a calculation formula that does not consider the influence of the viscosity of the medium. It is obvious from formula (1) that when the position height of a flowmeter float is determined, the measured medium density ρ is the only variable. If the measured medium density is different, the flow rate of the medium through the flowmeter is also different. Therefore, the scale correction is actually the flow correction.
If two media with different densities ρ1 and ρ2 pass through the same rotor flowmeter respectively, if the floats are balanced on the same solid, the basic formula for the density conversion of the rotor flowmeter is obtained from (1):
In the formula, P1, Tl and P2, T2 are two states of the same medium, which are respectively expressed by two parameters of pressure and temperature. It can be seen that, for the same gas medium, its density conversion can be completely converted into temperature and pressure conversion under different states. In this way, the calibration correction for measuring the flow rate of the same gas medium eventually becomes the temperature and pressure state correction (essentially, the density correction). Obviously, this is a correction method that is generally easy to achieve using a unit.
(A) How to obtain the actual flow value from the flowmeter scale reading at the use site?
When using off-the-shelf applications, there is only one purpose for transferring to a flow meter: to detect the actual flow of the measured medium. However, many using units ignore the difference between the on-site state and the flowmeter's calibration status (that is, the standard status), and directly use the flowmeter's calibration reading as the actual flow value of the measured medium. It is very obvious that this actual flow is unreal. It will bring errors to the measurement of the flow meter, which will cause errors in the final detection results of the supporting instruments.
In the field, the actual flow value is obtained from the scale reading of the flowmeter, which essentially converts the flow value under the standard state of the flowmeter into the flow value under the on-site working conditions. We set the parameters of the field conditions as actual flow Q, medium pressure P and temperature T; the relevant parameters of the rotor flowmeter scale are respectively the flow Q as compared to the standard state pressure Po and temperature To. According to formula (4):
Using the formula (5), it can be seen that the actual flow value of the measured medium can be easily obtained from the flowmeter reading on the spot. It is necessary to point out that when calculating by (5), P, P. , T, T. Should be substituted for absolute value, and P is the pressure before the meter, should be measured on the upstream side of the flowmeter, and close to the pipeline of the flowmeter.
Example: When using an air sampler, during operation, the rotor flowmeter on the sampler reads 500 ml / min, the front pressure of the meter is -100mmH 20 (due to the use of a suction pump, it is a negative pressure), and the site temperature is 30 ° C. Find the actual air flow value at this time.
The solution, based on the measured data, is here because P. Units of millimeters of mercury are used, so millimeters of water must be converted to millimeters of mercury. For calculations, simply divide millimeters of water by 13.6. From the results of the above example, it is seen that although the on-site state is not much different from the standard state, a difference of 22 ml / min (4.4% of the standard value) is produced for the measurement results. In other words, if the road is not modified, the flow value will produce an error of 4.4%!
? (Two) how to choose the appropriate glass tube rotor flowmeter according to the actual use flow?
This problem is exactly the inverse process of (1) above, and only needs to reverse the formula (5):
Here, Q is the actual flow rate; P, T, Po, To are all known. Qn calculated by [6] d is the scale flow rate value of the rotor flow meter to be purchased. Note that Q should be the usual flow. In order to ensure the flow chart, the pipette gauge has sufficient accuracy and margin when used, the upper limit of the glass rotor flow meter purchased should be 1.5 times of Qn.
We want to emphasize the importance of this clause, because if the pressure of the measured medium is large, it can never be ignored. For example, if the pressure of the measured medium is 3kg / cm2, and it is assumed that the temperature is not much different from the standard temperature of Testo and pipettes, then P = 3 + 1kg / cm2 (absolute unit, P. = 1). This gives Qn ÷ 2Q. That is to say, if the commonly used flow rate is Q, the appropriate upper limit of the flowmeter should be 1.5 × 2 Q = 3Q. In this case, the flowmeter is still selected according to Q, which will inevitably meet the requirements for use and cause production errors.
Rotary flowmeter density conversion can also be performed by graphic method.
The calibration correction when measuring liquid media often involves viscosity correction, which is very complicated and difficult to calculate. However, there are other ways to make up for it. Due to space limitations, I won't go into details here.