Regarding the calibration of double-flange level gauges
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For a double-flange pressure transducer with silicone oil as the medium, the density is set to 1. Assuming the medium inside the tank is water and the distance between the two flanges is 2.5 meters, for calibration with an empty tank, the range can be directly set to 0–25 kPa; based on theory, the range should be set to -25–0 kPa. Personally, I feel that the first method of setting the range requires an empty tank in order to be used, and I wonder if anyone uses this approach. What are the disadvantages of this method in practice? As for the second method, I think it is well-founded theoretically and has a scientific basis. I’d like to hear everyone’s opinions on these two methods of setting the range
This post was last edited by ylb913 on 2018-7-26 at 19:23. Regarding the negative pull in double-flange level indication, it is necessary to understand the density of the medium being measured and the density of the isolation fluid. The adjustment for negative traction is not done online, but rather in the laboratory, or before the gauge is installed on-site. It is incorrect to say that for calibrating an empty tank, one can simply reset the range to 0–25 kPa. Even when the container is empty, for a liquid level measuring instrument, the height difference of the silicone oil column with the negative pressure side being higher than the positive pressure side remains unchanged ； According to the theory, the range should be set at -25~0 kp – this is correct.
Don’t try to figure this and that out. Materials expand when heated and contract when cooled; the density of the sun, the moon, the stars, and other celestial bodies also changes throughout the year. The density fluctuates by 3% or 5% per year, just like when you go into heat once after another every year. The pressure difference corresponding to an empty tank is the zero point; shifting it corresponds to the amount of shift. The pressure difference corresponding to a full tank represents the full level; if there is no migration, then the level is measured using the two-point equation. .
I calculated the range using the theoretical formula, and it came out to -25 to 0. But I don’t understand: if there’s no air traffic control, can’t I simply remove the initial value of -25 so that I can start counting from 0?
I calculated the range using the theoretical formula, and it came out to -25 to 0. But I don’t understand: if there’s no air traffic control, can’t I simply remove the initial value of -25 so that I can start counting from 0?
It means setting the initial -25 offset, that is, clearing it, as the zero point. Is it reasonable to set the full scale at 25?
New to the instrumentation field; come and take a look, I’m learning*
Exactly, after the instrument is installed and fixed, the value read by the instrument when the tank is empty is the value that should be used for adjustment; there’s no need to calculate this value – doing so would just be pointless nonsense with no practical use. After performing the zeroing migration, estimate the working range using the hydrostatic formula ΔP = ρ·g·h, where h is the maximum liquid level; in your case, 2.5 meters can be used, but 3 meters might be better. ρ: The average density of the liquid being tested, in grams per cubic centimeter. g: The gravitational acceleration at the location where the instrument is installed, in meters per second squared. The estimated value is 9.8; as for the actual value, who knows whether it’s 9.79 or something like 9.76?
Your approach isn’t entirely unacceptable, but by setting the differential pressure of -25KPa to 0, there may be significant zero drift. Normally, the zero point is set with reference to atmospheric pressure; after making those changes and leveling the two flanges, if the transmitter shows 25KPa, zero drift could be severe.
I don’t understand it; the density of silicone oil isn’t 1 either. For an empty tank, just check what pressure is being measured right now – this pressure, plus the amount of water added, constitutes the set range. There’s no need to consider temperature or anything like that; a small amount of error isn’t a problem.
Once it’s actually installed, whatever value is displayed for the actual zero liquid level – as long as it matches, that’s fine