Fault in Siemens PS2 valve positioner
Thread Content
The last edit to this post was made by Refiner1234 on 2017-12-12 at 09:41. The inlet guide vanes of the air compressors in the PO/SM units are controlled using Siemens PS2 6DR5115-0EG00-0AA0 intelligent valve positioners, which feature a feedback display function! With the output remaining at 68%, the response value fluctuated suddenly, jumping significantly up and down within about 1-2 seconds; at the same time, the valve position on site reached its maximum value, before returning to normal after 30 minutes! The status at that time was definitely abnormal, but was the recovery after half an hour due to a soft fault in the locator? Why does the valve leak the most? Based on deviation adjustment, the valve should fluctuate in the opposite direction to the feedback. I would like to ask the experts here!
It’s strange; have you checked whether the feedback rod is loose?
On-site inspection was carried out on all connection components, and they were all tightened； The wiring is also not loose
For things like the inlet valve of the engine unit, it is recommended that you check whether there is any slight air leakage at the seal of the valve stem
How can fluctuations in feedback affect control? The situation you described is impossible
Is it locked at 33/90°? The valve position oscillations caused by feedback fluctuations – that’s the problem with PS2; the cylinder is too large, and areas where there is sticking cause poor performance. A larger dead zone will be better.
This should have nothing to do with air leakage in the valve stem; air leakage in the actuator causes fluctuations, while air leakage in the valve stem has little impact.
With Siemens flameproof positioners, there are many severe fluctuations in the field, and it’s impossible to identify the cause. We encountered a situation before as well: a batch of over 30 Siemens flameproof positioners were all showing fluctuations, and the Siemens technicians spent several days at the site investigating but were unable to find a solution. It just says it is not compatible with ABB’s DCS. Later, all were replaced with mechanical positioners, and all the problems were solved.
In my opinion, if the locator is not subject to severe interference, it is likely an issue with the assembly precision of the Siemens intrinsically safe locator before it leaves the factory; such problems cannot be detected during the factory testing. This kind of problem does not occur with Siemens intrinsically safe locators. I have disassembled and reassembled Siemens flameproof positioners many times. If this locator has a 4-20mA feedback output, its failure rate will be higher. (If it isn’t an original locator with feedback, the feedback board is added later; it is necessary to separate the flameproof locator in order to install the feedback board, and that’s where the problem lies.)
Try modifying the blind spot of the locator, or replace the safety barrier; I’ve encountered the same issue