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The measurement of the gas pressure in the ventilation pipe shall be carried out in the pipe section with relatively stable air flow. During the test, the static pressure, dynamic pressure and total pressure of the gas shall be measured. The orifice for measuring the total gas pressure shall face the direction of the air flow in the air duct, and the orifice for measuring the static pressure shall be perpendicular to the direction of the air flow.

用U形壓力計測全壓和靜壓時，另一端應與大氣相通(用傾斜微壓計在正壓管段測壓時，管的一端應與大氣相通，在負壓管段測壓時，容器開口端應與大氣相通)。因此壓力計上讀出的壓力，實際上是風道內氣體壓力與大氣壓力之間的壓差(即氣體相對壓力)。大氣壓力一般用大氣壓力表測定。由于全壓等于動壓與靜壓的代數和，可只測其中兩個值，另一值通過計算求得。

When the U-shaped pressure gauge is used to measure the total pressure and static pressure, the other end shall be connected with the atmosphere (when the inclined micro pressure gauge is used to measure the pressure in the positive pressure pipe section, one end of the pipe shall be connected with the atmosphere, and when the pressure is measured in the negative pressure pipe section, the open end of the container shall be connected with the atmosphere). Therefore, the pressure read out on the pressure gauge is actually the pressure difference between the gas pressure in the air duct and the atmospheric pressure (i.e. the relative pressure of the gas). Atmospheric pressure is generally measured with an atmospheric pressure gauge. Since the total pressure is equal to the algebraic sum of dynamic pressure and static pressure, only two values can be measured, and the other value can be obtained by calculation.

山東通風管道

Shandong ventilation duct

測定儀器

Measuring instrument

氣體壓力(靜壓、動壓和全壓)的測量通常是用插入風道中的測壓管將壓力信號取出，在與之連接的壓力計上讀出，常用的儀器有畢托管和壓力計。

The measurement of gas pressure (static pressure, dynamic pressure and total pressure) is usually to take out the pressure signal with the pressure measuring pipe inserted into the air duct and read it on the pressure gauge connected to it. The commonly used instruments are pitot tube and pressure gauge.

1畢托管

1 pitot tube

(1)標準畢托管

(1) Standard pitot tube

它是一個彎成90°的雙層同心圓管，其開口端同內管相通，用來測定全壓;在靠近管頭的外壁上開有一圈小孔，用來測定靜壓，按標準尺寸加工的畢托管校正系數近似等于1。標準畢托管測孔很小，通風管道內易被粉塵堵塞，因此這種畢托管只適用于比較清潔的管道中測定。

It is a double-layer concentric tube bent into 90 °, and its open end is connected with the inner tube to measure the total pressure; A small hole is opened on the outer wall near the pipe head to measure the static pressure. The pitot tube correction coefficient processed according to the standard size is approximately equal to 1. The standard pitot tube measuring hole is very small, and the ventilation pipe is easy to be blocked by dust. Therefore, this pitot tube is only suitable for measuring in relatively clean pipes.

(2)S型畢托管

(2) S-type pitot tube

它是由兩根相同的金屬管并聯組成，測量時有方向相反的兩個開口，測定時，面向氣流的開口測得的相當于全壓，背向氣流的開口測得的相當于靜壓。由于測頭對氣流的影響，測得的壓力與實際值有較大誤差，特別是靜壓。因此，S型畢托管在使用前須用標準畢托管進行校正，S型畢托管的動壓校正系數一般在0.82～0.85之間。S型畢托管測孔較大，通風管道內不易被粉塵堵塞，這種畢托管在含塵污染源監測中得到廣泛應用。

It is composed of two identical metal tubes in parallel. During measurement, there are two openings in opposite directions. During measurement, the opening facing the air flow is equivalent to total pressure, and the opening facing the air flow is equivalent to static pressure. Due to the influence of the probe on the air flow, there is a large error between the measured pressure and the actual value, especially the static pressure. Therefore, the S-type pitot tube must be corrected with standard pitot tube before use. The dynamic pressure correction coefficient of S-type pitot tube is generally between 0.82 and 0.85. The measuring hole of S-type pitot tube is large and it is not easy to be blocked by dust in the ventilation pipe. This pitot tube is widely used in the monitoring of dust pollution sources.