Flow zero-point correction and small-signal cutoff point of electromagnetic flowmeters

The zero-point correction is equivalent to resetting the system’s zero point, while small-signal rejection is merely a technical measure that prevents signals below a certain level from being displayed. It has no impact on the accurate measurement of the flow meter

Zero-point correction is used to adjust the physical zero offset of the instrument itself. Small-signal rejection is like holding back feces without flushing and then covering the toilet lid – it’s putting a bandage on a wound; it’s deceiving oneself, others, and the whole world. The measurement accuracy becomes as poor as that of feces, as if it’s been crudely covered up. Do you understand? Mara Gobide.

Thank you to both experts for their answers. Let me explain my specific situation: I have 3 flow meters, 2 of which are installed on 2 branch pipes, while 1 is installed on the main pipe. The flow meter on the main pipe shows a certain flow value when the fluid is at rest; I applied a zero-point correction to eliminate this issue. However, I found that the flow rate measured by the meter on the main pipe was still 60 m3/h higher than the sum of the flow rates from the branch pipes. After contacting the manufacturer, they advised me to set the zero-point correction value for the meter on the main pipe to 0 (it was previously set at +42). With this setting, the FS value became -66. I also enabled the low-signal cutoff function, and after doing so, I noticed that the flow rate measured by the meter on the main pipe was still 20 m3/h higher than that of the branch pipes. How should I adjust these settings? Also, I read in the instructions that the zero-point measurement value FS should be 0, but this is quite different from the FS value of the flow meter on the main pipe. Is there a problem with this?

1. A flow meter is a dynamic measuring instrument; when the flow rate drops to a certain level, the measurement equation used in its programming is no longer valid. This is significantly different from instruments that are static in nature, such as pressure gauges. . . Those guys from the flow meter manufacturing company really are awful; they don’t explain things clearly to you. Instead, they write the measurement range of the flow meter as 0～X. . . To put it more bluntly, many flowmeters have a measurement dead zone, or what is also called a measurement uncertainty zone, or a zone of measurement ambiguity. . . So, the inaccurate zero point of the flow meter should be regarded as a zero offset, but I’m not sure if that’s the right approach Perhaps the meter is still within its normal operating range, with no deviation yet.....

2. There are three flow meters, and the sum of the readings from the main meter and the sub-meters does not match. This kind of thing is too common. A few days ago, a member of the community specifically posted a question regarding this matter. The so-called accuracy of flow meters can be considered nothing more than a gimmick; it’s best not to take it too seriously.

3. For the three flowmeters, don’t zero or calibrate them yet. Apply small signal rejection to all of them; don’t set the rejection level too low. Then compare the value shown on the main gauge with that on the sub-gauges to see how much the difference is. Adjust the zero-setting of the main gauge accordingly until the values are close to each other. 4. Strictly speaking, this shouldn’t be called debugging – it’s more like making adjustments arbitrarily to get the values to match. Anyway, the manufacturer can’t do much to help you; just make things up and get the work done, that’s it.

Everyone explained things very well; I learned a lot

Try to avoid making zero-point adjustments if possible. To put it another way, if you do make such adjustments, the final result will only become more chaotic. It’s better to simply remove low-level signals in a uniform manner; for example, if the supervisor requires values below 1, the person in charge of that aspect should do the same