Doubts regarding 2 cases of instrument issues in production – A beginner seeks answers
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Hello, experts. I am the operator; I noticed two issues with the instruments when I took over the shift the day before yesterday during the daytime shift. One is that for the liquid level in our air separation water cooling tower, a three-out-of-two configuration is used; both level sensors are of the double-flange type and are at the same horizontal level. There is a root valve above and below each level sensor, along with a transmitter. This is because there is a large difference in the readings of the three level gauges; the reading of gauge A is close to that of the magnetic flip-type level gauge on site, while the readings of gauges B and C are similar but about 100 mm lower than that of A. After reporting it to the instrument maintenance technician, he said that the level gauge needed to be removed, then pressurized and something else done, followed by calibration – it was all very confusing to me. Later, since other tasks had to be done, other people went ahead and handled it. I asked my colleague how they did it; they said they used something called 475 to check it, did some calculations, and then it was fixed. . . I, being rather inexperienced, would like to ask how this instrument technician managed to handle it? Secondly: After the expansion oil pump started operating, the oil temperature behind the cooler (that is, the temperature of the oil supplied to the lubrication points) kept rising. I asked the personnel on site to check the pipelines, and the temperature was normal, around 20 degrees; after a while, this temperature dropped again, and the instrument registered this change. It wasn’t me who handled it; I asked a colleague about the process used. He said that they wiped the thermocouple with a cloth (I’m not sure whether that’s a thermocouple or a thermal resistor; the instrument repair technician said it was a thermocouple). They tried to pull the thermocouple out of its housing in order to wipe it, but they couldn’t do so. . . Then the instrument worked normally. It is said that there was oil in the thermocouple junction box – how can this be explained? I hope an expert can help me solve this puzzle; thank you in advance
First, it is to adjust the zero points so that they are all the same. Second, there are conductive substances at the thermocouple terminals that cause false readings
First question: If everything was working normally before, it might be worth flushing the pipes of the transmitters that show discrepancies in order to rule out pipeline-related issues; yet that didn’t work either, as all the transmitters showed a reading of zero. The second issue is likely poor wiring contact.
The first issue is likely an incorrect migration amount or an incorrect differential pressure range; correction should be performed based on the known values. When choosing two out of three, chain reactions often occur, so caution is required when dealing with it.