There are many common flowmeters suitable for measuring tiny, such as differential pressure, float, volumetric, etc. Some of these flowmeters are suitable for measuring both large and small flows, while others are specialized for measuring small Flow design.
1, Differential pressure flowmeter
The differential pressure type flowmeter, which is composed of a standard throttle device and a differential pressure type, is subject to three levels of limitation in small flow measurement.
Is limited to the size of the pipe diameter. Standard throttling device is suitable for pipe diameters of 50mm and 50mm. The pipe diameter is too small, and the diameter of the throttling device is relatively reduced, and it is difficult to carry out similar production and processing as required in the specification. Zh
The second limitation is that the gas pressure is small. This gas pressure is proportional to the square meter of the water flow rate. When the water flow rate is low to a certain standard value, the gas pressure becomes less and less so that it cannot be distinguished.
The third limit is the lower limit of the Reynolds number. Throttle device types are different, and the lower limit of Reynolds number is also different. Generally speaking, Reynolds number ≥104 is the boundary that can be applied. The mean water flow and the flow corresponding to the lower limit of the Reynolds number are the measurement lower limits of the small flow. The Reynolds number is very small, and the emission index will cause a significant change with the change of the Reynolds number, and even increase the uncertainty. Zh
2, float flowmeter
Float flowmeter is composed of float and conical tube. The cone tube in the glass test tube float flowmeter is a glass test tube; the cone tube of the metal hose float flowmeter is made of metal material, the hydrodynamic temperature reaches 180 ° C, and the hydrodynamic working pressure reaches 13MPa.
The float meter is a medium-mild instrument panel. The basic deviation of the float meter for metal materials is 1% ～ 2.5% FS for on-site marking, and 1% ～ 4% FS for remote transmission. The caliber glass test tube float meter is 2.5. % To 5% FS. Therefore, generally only the flow monitoring is applicable, not the carry-over measurement verification. Zh
The glass test tube float flowmeter is only suitable for vapor and liquid with higher definition, otherwise the aspect ratio of the float in the conical tube is not easy to recognize. The metal hose float flowmeter is not limited. Zh
The flow measurement range of the caliber float meter has long been incapable of doing much, in which water is 0.3 to 3 L / h and gas is 5 to 50 L / h. Eco-environmental protection uses a large number of atmospheric samplers, free online analyzers, laboratory analyzers, and other widely used small-sized laminated glass float flow meters. The measurement scope can be smaller.
In the liquid level meter, flow rate and relative density measurement of the entire process of industrial production, if the measured substance has a large viscosity or corrosion. Common air blow inspection or liquid blowing methods are used to carry out protection. Air blow inspection and liquid flow measurement are usually measured by float flowmeters. In the place where the working pressure of the gas (liquid) source fluctuates greatly or the working pressure of the measured substance fluctuates greatly, in order to make the air blow inspection and the flow of the liquid blown stable and accurate measurement, some products use a float flow meter and a controller Constant current device) is equipped with a set of constant gas pressure flow controller.