【Q&A Question 159】2017.06.08
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This post was last edited by 955559 on 2017-7-21 at 23:13. [Q&A Question 159] On 2017.06.08, when using a differential pressure transmitter to measure liquid level, zero adjustment is sometimes required. What is zero adjustment? What is the purpose of zero adjustment? The reference answers can be seen after responding; points will be awarded for identifying the key points. (Unless otherwise specified, all questions and answers are based on hydrogenation units.) Zero-point adjustment involves moving the zero point (the starting point) of the gauge without changing its range; in other words, it involves adjusting the upper and lower limits of the gauge. The purpose of this is to eliminate the effect of fixed pressure differences, so that the gauge can accurately reflect the level of the liquid. Scoring criteria: 2 Wealth points for incorrect attempts; 3–8 points for *incomplete* answers. 10 Wealth points for correct answers, provided with detailed explanations; 15–20 Wealth points for correct answers with additional *insufficient* details. Please score according to these criteria. Note: If there are editing records after answering, only points will be awarded to those who participated. For continuous malicious spamming, 2 points will be deducted each time, with no upper limit. Pure numbers, pure emojis, or random letters that have nothing to do with the answer are all considered malicious spamming; points will start to be deducted after three warnings. 2017 Q&A Summary Thread (updates have begun) http://bbs.hcbbs.com/thread-1657793-1-1.html 2017 Daily Question Summary Thread (updates have begun) http://bbs.hcbbs.com/thread-1657794-1-1.html 2016 Q&A Summary Thread (updates completed) http://bbs.hcbbs.com/thread-1597792-1-1.html
Zero shift is the adjustment of the zero point away from ‘zero’, so that the output starting point of the transmitter corresponds to the starting point of the quantity being measured
Changing the zero point or range is intended to make the lower limit and range match the actual measured values
Zero-point adjustment involves moving the zero point (the starting point) of the gauge without changing its range; in other words, it adjusts the upper and lower limits of the gauge. The purpose of this is to eliminate the effect of a constant pressure difference, so that the gauge can accurately reflect the level of the liquid.
Definition: Moving the level gauge zero point up or down. Reason: When the liquid level is at zero, due to issues with the installation height, the differential pressure gauge does not indicate zero; instead, it shows a positive or negative reading deviation. To ensure accuracy and eliminate this fixed bias, the zero point is moved downward or upward, that is, a “zero shift” is performed”
Zero-point migration: When the zero point of the medium under test does not match the actual zero point, it is necessary to adjust it to the actual zero point before proceeding. The purpose is to accurately measure the liquid level.
When using a differential pressure transmitter to measure liquid level, due to the different installation positions of the transmitter, the positive and negative pressure conduits are filled with liquid, and this liquid creates a constant differential pressure in the transmitter. When the liquid level is at zero, this results in an indication deviation, causing the differential pressure gauge to indicate a value other than zero, either positive or negative. To ensure accuracy and eliminate this fixed bias, the zero point is moved downward or upward, which is known as “zero shift”.
The change in the output voltage from zero when the input voltage is zero. It is also abbreviated as zero drift. How does zero-point drift occur? Operational amplifiers use direct coupling; we know that in a directly coupled amplifier circuit, the Q points of each stage influence one another. Due to the amplification effect at each stage, a slight change in the first stage can result in a significant change in the output stage. When the input is short-circuited (due to slight changes in the Q-point of the input stage for various reasons such as temperature), the output will change slowly over time, resulting in zero drift. The cause of zero drift is that the parameters of the crystal transistor are affected by temperature. The most effective measure to address zero drift is to use a differential circuit.
Zero-point migration refers to the change in the liquid level zero point, with the aim of enabling more convenient and practical measurement of the liquid level
Zero-point migration refers to the change in the liquid level zero point, with the aim of enabling more convenient and practical measurement of the liquid level
Due to the height difference between the positive and negative pressure conduits caused by the installation location of the transmitter, measurement errors occur; therefore, zero point adjustment is necessary to eliminate these errors