The on-site indication of the float level gauge is normal, while the DCS indicates the maximum value. Fault analysis
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The on-site indication of the float level gauge is normal, and it matches that of the glass plate. But DCS shows the highest value. The output current of the field transmitter is normal and corresponds to the liquid level. The safety barrier in the cabinet room measures a current of 20 MA, so the DCS shows the maximum value. It indicates that there is no problem with the cabinet room; the issue lies on-site. During the on-site inspection, it was found that water had entered the junction box located not far from the transmitter; after the water was removed, the DCS displayed normal readings. I analyze that it is the water inflow (which is not severe) that has divided the entire circuit into two circuits. At the site, due to the high impedance of the transmitter terminal connections, this circuit is functioning properly, and therefore the current is also normal. The safety barrier in the cabinet room has low impedance, and shorting this circuit results in 20 MA. I’m not sure if my analysis is correct Please analyze it.
This is a very common instrument failure phenomenon. Water can conduct electricity; when there is a voltage, an electric current is generated, which then flows in parallel with the current from the transmitter and enters the DCS side.
Can the original poster talk about the two circuits? I don’t quite understand what you mean! ?
I have encountered this problem; the meter in question is an electromagnetic flowmeter. However, the cause of the fault is the same in this case as well. Water gets into the wiring box, resulting in an incomplete short circuit between two wires. This creates a parallel circuit with the meter on site, but the current at the point of short circuit is very high, so the current throughout the entire circuit becomes high as well. As a result, the DCS shows a value that is too high or at its maximum. The meter on site, on the other hand, can still function properly because the voltage remains sufficient for it to operate correctly, so its readings remain normal. These are my analyses; they are provided for reference only.
I basically agree with your judgment, but I need to confirm it.
Hi, it’s quite simple: the signal output cable is damaged and comes into contact with metal components, which causes leakage current. I’ve encountered it before; with a careful search, it can be re-bandaged.
I think this issue is interesting enough to discuss; I’ve encountered this phenomenon as well, but not to the extent that the person above mentioned. I’ve learned from it.
Inaccurate measurements due to water ingress are happening quite often these days; hehe, no one really thinks much about the specifics. The original poster has thought this through quite carefully. Valve potentiometers are also prone to such problems
I think it was the high current at the site that caused the safety barrier to limit the current.
This situation usually occurs at the wiring boxes or the wiring terminals of instruments (valves); poor waterproofing allows water to get in, which can lead, in mild cases, to the problems mentioned by users, while in more severe cases it can cause damage to the instruments and related components. Therefore, it is essential to take proper measures to protect against thunderstorms during summer, as this is just as important as preventing freezing and condensation in winter.
It can only be said that I’m not at the beginner level yet; I need to study hard here*.