Have you encountered situations where the DCS display shows a value with a ‘U’, such as 1.2UMPa?
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This post was last edited by uclove on 2018-1-18 at 12:04. An Allen-Bradley system is being used; the current and pressure values from the field are passed through a Wison safety barrier before being fed into the DCS. Under normal display conditions, 7 of the current and pressure readings show a ‘U’ symbol, and the historical trend data is displayed as dashed lines, indicating that there should be a loss of connection. However, by disconnecting the safety barrier signal at the endpoint wire and reconnecting it, normal display is restored. Since there is no measurement signal, it is also impossible to determine where the problem lies. Moreover, the 7 abnormal signals are not on the same card, nor are they in the same control station; no issues were found in the grounding measurement of the control cabinet. Perhaps I didn’t explain it clearly; a signal with a U symbol appeared. At that time, I simply untied the wires and connected them again, and the problem was resolved. I didn’t measure the signal, and such an issue has not occurred again recently. I would like to know if anyone has encountered this situation and what the cause might be
This post was last edited by 1111111 on 2018-1-17 at 13:16. Do you have a way to reproduce the fault? . . . If not, then it’s haunted! . . . What’s the point of worrying over such trivial things? I guess you’re the person who wrote the program for DCS; he might not understand either why a ‘U’ appears there. Just like when a small pimple appears on your face, can’t you figure out why? :Lol, the ghost has possessed your soul – what bad luck! Didn’t your teacher teach you anything? . :Besides, even those experts are too busy; they won’t waste time on your little issue. If they were to check the code, where would they find any minor defects? , or check if there are any issues with the display screen? Those top experts earn annual salaries of 1 million or even 100 million – serving you would require a lot of effort and time with no tangible benefits, so it’s not cost-effective for them :lol
For analog signals, in Hilscher this is considered an out-of-range condition, that is, when the incoming signal is below 4 Ma or above 20 Ma
The key is to untie the wire and then reattach it, and it works again; this doesn’t make any sense
Check whether the current signal is out of range
Are these several field instruments similar to each other? Do they all enter the control room through the same cable tray? If so, it’s necessary to check whether there is any external interference causing signal fluctuations that lead to faults
It’s just a loose connection in the cable; there’s no need to worry about it. What is the cutoff in milliamps? Zero An! What is the specified range? 4~20 milliamps! So for fried eggs, isn’t 0 milliamps beyond the range? ? ? It’s easy to understand.
Has the card or safety barrier locked up due to severe interference? Must a signal be sent to restore it?
If the current signal exceeds the limit, this alarm may occur
Variable breaks usually come with quality markings that make it visible, so this isn’t likely to be a simple break. It’s still possible that interference is at play; as mentioned on the 8th floor, it would be advisable to check with Allen-Bradley to see if there is any mechanism that requires the connection to be disconnected and reconnected in order to overcome such interference. Also, check whether the shielding layers of these signal wires are properly grounded.
This post was last edited by uclove on 2018-6-20 23:08. This issue has occurred twice again in the past two days: first, the motor temperature fluctuated without any pattern, and after about 2 hours, the temperature dropped to zero and stopped being displayed. There was no issue with the temperature itself; the installation was completed within two days, and there were no areas of friction. At that time, no large electric devices or variable frequency controls were in use within the system. By disconnecting and reconnecting the connections of the thermal resistor on site, the problem was resolved, and the system has been operating stably ever since. Secondly, yesterday there was a situation where a voltage value of U appeared on the display along with readings related to pressure and current. Since this had happened before, no wiring was disconnected for inspection this time. First, a FLUKE clip-on milliammeter was used to measure the current, and the 4-20mA range was maintained; the readings matched those displayed, and the fluctuation curve was normal. Only after the wiring was disconnected and reconnected did the U value stop appearing on the display. The system grounding and the cards have all been checked on-site by HILITE’s technical staff, and there are no issues. Moreover, this problem only occurs with this one device; it’s difficult to figure out the cause, which is quite frustrating