Volumetric expense and volumetric flow meters.
The basic means of the gas expense measurement nowadays are the devices of the alternating drop of pressure. It places the 90 of the main part of all flow meters. It is used to say that the error of these device measurements after their assembling lies in the boundary 1-5. This boundary is used for the upper part of the scale device range. The role of the primary elements of this type of flow meters plays the restriction device сужающее устройство, pressure tubes, etc. The general for the alternating pressure drop flow meters is that the signal, formed by the primary element is proportional to the square of velocity of the flow. Due to this the scale is non-linear, it bounds the measurement range and causes the progressive increasing of the error under the condition that the quantity of the measured expense value is less than 20-30 from the upper limit of the scale.
To the primary elements of the alternating pressure drop flow meters are the pressure tubes.
If the velocity field in the pipeline is symmetrical, then the pressure pipe is placed in one position for the measurement of the average and maximum velocity. The second class of the volumetric flow meters can be represented by the displacement of the sensitive element proportionally to the value of the expense of the circumfluent22 обтекающий it s flow. They can be rotameters, floating, spring and rotation flowmeters. Figure1 The error of their measurement is from 1to 4 in the range under 50 thousand. The basic view of the rotameter is shown on the Figure 2. The wide extension among the volumetric flowmeters the tachometric has got. They have the primary element, and it s rotation speed is proportional to the gas expense.
Tachometric flowmeters can be used for the measurement of the big gas expanse under the high pressures they have linear output and low sluggishness. The alternation in measurements is 1. The new category of the volumetric gas expense measuring devices constructed 2 flowmeters that were designed in the USA. The first one is vortex33 вихревой precession and the second one is vortex hydrodynamic.
In both constructions the movable part is absent. The measuring range is 100-1, caliber from 50 to 152 mm, error 1 and lower. The vortex precession case looks like the Ventura tube. The hopper44 воронка with screwing vane on the input gives the gas flow rotation motion, after this it goes to the wider part of the case. It goes there in the form of the vortex.
Under the condition of the flow expanse it descends an axis and moves straightly by the spiral. This motion is called the vortex precession. The frequency of the vortexes passing is fixed by the thermal pickups and electrical devices is transformed in the expanse value. The vortex hydrodynamic expanse is based on the principle that was marked by the pocket. If in the channel perpendicularly to the gas flow the cylinder will be placed, then it s butts55 торец will have the set of the following each other vortexes.
Due to them the flow will obtain the oscillating view. In these flowmeters the direct proportionality between frequency of such vortexes creation and volumetric expense of gas is used.