Measurement instrument issues
Thread Content
I would like to ask what is the relationship between the local gauge, that is, the instrument that displays the measurement parameters on site, and the display in the DCS system in the control room? At work, I encountered a problem: the measurement values shown on the instruments on site were correct, but the control room displayed an incorrect negative value. The instrument technician said that a component in one of the instruments had burned out, and replacing that component resolved the issue. What I want to ask is: since a certain component on site is damaged, why does the value shown by the gauge at that location correspond to the correct value, while the display in the control room shows an incorrect value? Another question arises: in the case of interlocked instruments, if this situation occurs – where the gauge on site shows the correct value while the gauge inside the room shows an incorrect one – will the interlock still be activated? In other words, does this chain receive signals from the on-site panel or from the signals inside the control room?
This post was last edited by Taohualing Jushi on 2016-1-7 at 09:47. The on-site readings are correct; the issues lie with the DCS system: 1. The transmitter is damaged; 2. The DCS cards are faulty; 3. The range settings of the DCS are incorrect; 4. The feedback signal wires are subject to interference, are loose, or broken. Regarding interlocks: if it’s an interlock within the DCS system, then obviously the DCS readings take precedence, as the on-site readings, regardless of their accuracy, do not enter the control system and are only used for reference
Generally, the situation is the same, but it is also possible for things to differ. 1. The circuit is incorrect; the value at the site is the accurate one, while the value in the DCS system is incorrect ； 2. The DCS range setting is incorrect ； 3. DCS sets coefficients or other formulas and displays the corrected values. I have encountered these types, and there may be other situations as well.
Another option is to display the value from just before the circuit breakage after it occurs. Chain operations are related to central control.
This post was last edited by zxb1990 on 2016-8-6 at 20:03. There are several reasons why the values at the site do not match those in the control room: 1. The range set for the transmitter at the site is different from the range used in the control room； There is a problem with the output of the 2 transmitters; their linearity does not meet the requirements ； There are issues with the analog-to-digital conversion in the 3 control station DCS systems, etc ； 4 There are issues with devices such as those that have temperature sensitivity or those connected via safety gates. . . . . .
So that means if the situation I mentioned occurs, it could lead to incorrect operation of the interlocks, right?
I dare to ask: is the reading inside obtained by re-converting and transmitting the data from the local meter? So in that case, if the meter on-site is incorrect, then the meter inside the room will definitely show an incorrect reading as well? To put it simply, I just want to ask what the relationship is between the on-site gauge and the indoor instruments? Is it independent or related?
Yes, if this error value is within the range that can cause a chain reaction. However, obvious error signals are generally suppressed within the program; there are error alerts available
I have a gentle question: what is a host computer?
What do you mean by \"Generally, obvious error signals are suppressed within the program, with error alerts provided\"? How does that work? Does it mean that if there is an obvious error, the system prevents it from causing further issues, and only an error alert is given?
If the DCS program is taken into account, a cascade reaction will not occur when there are errors in the peripheral signals, and there is also a mechanism for detecting whether the peripheral signals are incorrect