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.
的选型和安装的品种及选用 I. Selection and installation of glass rotor flowmeters
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 instrument series spectrum developed by the country, 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) 1 ml / min to 1000 cubic meters / 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.
的选型和安装的刻度修正 Second, the selection and installation of glass rotor flowmeter calibration correction
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.
流量一般表达式式(1)是不考虑介质粘度影响的计算式。 The following is the general expression of the flow rate of glass rotor flowmeter (1) is a calculation formula that does not consider the influence of medium viscosity. 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 conversion of the density of the rotor flowmeter is obtained from the formula (1): where P1, Tl, and P2 , T2 are the 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 scale 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 in general units.