Does the length of the pressure gauge pressure lead affect the measurement results?
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This post was last edited by 2005180005 on 2018-10-8 at 15:28. Does the value shown on the gauge represent the pressure at point B, or the pressure at a point 0.5 m above point B? In other words, does the length of the pressure lead pipe affect the measurement results? If there is an impact, then the pressure gauge should be as close as possible to the measurement point?
I’m not sure what level of precision you need; ordinary precision is sufficient and can be ignored. For more accurate remote measurement, it is best to use digital instruments with converters.
If there is a height difference between the instrument and the measurement point, measurement errors occur due to the gravity of the medium in the pressure conduit; this medium is liquid, while the effect of gas can be ignored.
1. The values shown in the diagram are, of course, except for the value at 0.5 meters above point B. 2. Then, can the measurement taken at 0.5 meters be used directly as the pressure value at point B, without any adjustments? To figure this out, we first need to see how high the pressure you are measuring is. 3. Just as when you step on a scale to weigh yourself, would it affect the accuracy of the weight measurement if you let out a fart, or a double-fart, or a series of farts? 4、........ :P
What was said upstairs is very insightful. In my opinion, as long as the pressure is slightly increased, such errors can be ignored; of course, since liquids have their own weight, the effect seems more noticeable.
It’s not just the issue of height difference; there is also fluid friction and static friction at play (for example, several kilometers away from a pressure source, there is inevitably a pressure drop). As ever, it depends on the desired precision and range – generally speaking, this level of error can be ignored.
““The impact of measurement results”? This needs to be divided into dynamic effects and static effects. It also depends on the medium being tested. On the premise that the pressure gauge tube is filled with the medium under test: 1. If the medium under test is a liquid, according to the principle of hydrostatic pressure, when the pressure remains constant, there is a difference of 0.5 units corresponding to the height of a liquid column between the pressure at the gauge point and that at point B; this difference can be ignored when the pressure is high enough ； When pressure changes, due to the incompressibility of the liquid, the pressure change is immediately transmitted to the gauge point. 2. When the medium under test is a gas, and the pressure remains constant, the pressure at the gauge point is the same as that at point B. When pressure changes, due to the compressibility of gas, the gauge pressure does not change immediately; its change is determined by the volume of gas in the pressure guide tube. The larger the volume of gas in the pressure guide tube, the slower the change in the gauge pressure. Summary: The shorter the pressure lead, the better.
If the length of the pressure tap pipe is too long, there will be some delay, especially with measurement media that have a higher viscosity