Everyone has encountered some strange things; let’s share them and discuss them
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I believe that like me, you all often encounter many \"strange things\" in your daily work; some of them are impossible to understand, while others become clear after some thought. Everyone is welcome to share these strange occurrences so we can discuss them together.
In the same city, under the same sky. Separated by a river, one side has clear skies while the other is hit by heavy rain. I would be grateful for the master’s guidance on how to interpret such visions.
On one side is seawater, on the other side is fire.
Once, an electrical distributor installed inside a cabinet, along with a two-wire radar level gauge, produced a 4–20mA signal of around 18mA when sending it to the PLC; this value was higher than the actual liquid level. During on-site inspection, the level gauge had a supply voltage of 18.6V and an output of 10mA at multiple points. During line inspection, it was found that when the circuit was open at the site, the resistance measured at the distributor end was over 1 kΩ. It works normally after replacing the cable core wire.
During one of my shifts, the readings from an electromagnetic flowmeter kept fluctuating. When I went to the site to check, everything seemed normal. I checked the grounding wires as well, and they were fine too. Then I swapped one of the signal wires with another nearby wire; after that, the readings became normal again. Once I switched the wires back to their original positions, the fluctuations stopped. To this day, I still don’t understand why that happened
It was originally about control aspects, but no satisfactory response was received after publication. I’m going to try my luck with the instrument panel today. The day before yesterday, there were abnormalities in the custom control loops of the Zhejiang Zhongkong ECS100-DCS system, but the cause was unknown. 1) The four digital inputs that showed abnormalities were located in the first four channels of the AI cards. 2) Based on the trend data, it was the MV values that changed first, with the PV values changing subsequently. 3) The AO outputs related to these loops were located on different AO cards within different chassis. 4) The MV values changed over a period of about 5 seconds; in some cases the pattern was an inverted triangle, while in other cases it was an upright triangle. 5. It appeared for the first time, and for a short duration. Can anyone help analyze it?
It’s like sometimes you can’t find something no matter how hard you try, but once you try again after some time, it shows up! It’s really strange!
It cannot be said that there is any abnormality in the 4 AIs, as there is no change in the PV values; it is the MV values that show abnormalities. The PV value responds appropriately to changes in MV.
Do you mean that there is a connection in the middle of the cable, or that the copper wires come into contact with the shielding after damage, or that the copper wires are grounded?
Has the grounding resistance of the ground wire been measured? I think it must be caused by some interference
I can’t think of it; the moderator should provide a detailed trend chart for this issue, one that shows the data over two minutes when zoomed in, and analyze it based on the trend per second. To be honest, I’ve never encountered such a problem before