Troubleshooting of Siemens SIPART PS2 flameproof enclosure type locator

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Fault description: The operator reported that even after the FV-801 valve was closed, the flow meter still indicated a high flow rate. In fact, this valve is a 90-degree swing ball valve; the SIPART PS2 positioner does not provide a position feedback signal. When the operator says that the valve is fully closed, it means that the MV value of FIC-801 is 0, and based on this, the operator assumes that the valve is indeed closed. First processing step: After receiving feedback from the operator, I also checked the process display on the DCS; indeed, the MV value of the FIC was 0, but the PV value showed 240 m3/h. I’m very puzzled, as this valve has been in use for 10 months and this kind of problem has occurred for the first time. The first thing that comes to mind is that someone might have changed the setting parameters 7.SDIR and 38.YDIR of the locator, resulting in the control signals from the DCS being in the opposite direction to the actual opening and closing direction of the field valves. Upon arriving at the site, I checked the display screen of the locator; the first line of the display showed 0, while the second line displayed AUT0. Everything seems normal, but upon closer inspection of the actual position of the valve, it was found that the valve is actually at around 80% of its full position. The first thing that came to mind was to perform automatic verification again. Before automatic verification, the settings of parameters 1 and 2 as well as the settings of the gear ratio selector were checked, and all met the requirements for angular travel actuators. Therefore, after manually driving the valve to 50% position, an automatic calibration was performed. When moving on to the second step, the locator displays an error message: ㄣd___U (this symbol is difficult to type; see Image 1). Follow the instructions to adjust the friction clutch (the flame-retardant type of friction clutch is located outside the locator; a longer screwdriver can be used to turn it by inserting it into the small holes on the circumference of the friction clutch, as shown in Image 2) until the bottom row of the display shows d_0_U. Press the + button to proceed with the verification. It automatically moved to the third step, and after waiting for 10 minutes, it still didn’t end. The automatic initialization was interrupted by pressing the hand-shaped button. I tried manual initialization, but when the actuator was moved to the ends of its travel range, it was found that the potentiometer reading fell outside the allowed range, that is, it was not between “P5.0” and “P95.0”. I adjusted the friction clutch several times, but it still couldn’t reach the range between “P5.0” and “P95.0”. Thus, forced manual initialization is carried out, and just like with automatic initialization, it is not possible to proceed to the third step. Manual initialization was interrupted by pressing the handshape button. I tried automatic initialization again, but it got stuck at step three and was unable to proceed. So I performed manual intervention by gently turning the friction clutch; the valve suddenly moved, completing the third step and moving on to the fourth step, thereby finalizing the automatic initialization. When checking the valve position, it was found that the deviation between the actual upper and lower positions of the valve was significant. Within a travel range of 0%-90%, there was a deviation of around 3% between the set value displayed on the screen (the value on the second row of the display) and the actual position indicated (the value on the first row of the display). When the set value was 100, the position indicated on the screen was 90%, and an error alert code ㄣ1 also appeared on the bottom row of the display. After great effort, the operator wanted to put it into use as soon as possible, so they told the operator that the valve had been adjusted and could be used. A month later, the same fault occurred again. That is, after the valve is closed, the flow meter still shows a high flow rate. It seems the fundamental problem remains unresolved; the cause of the fault has not been identified. Learning from the mistakes of the previous failure, this time the locator was directly removed from the actuator to check for any issues with its connections. As expected, the coupling wheel came loose and was pulled right off the shaft of the locator. The coupling wheel was reinstalled and tightened in accordance with the instructions (see pages 9 to 10 of the attachment). After reinstalling the locator on the actuator, automatic initialization was carried out again. During this process, in step two, the friction clutch was rotated as instructed to eliminate the error message ㄣd___U (this symbol is difficult to type; see Image 1). Steps three through five were completed smoothly. Subsequently, its valve position was checked; both the set value displayed on the screen (the value on the second row of the display) and the position indication (the value on the first row of the display) were within a deviation of 0.5, and the accuracy for the upward and downward movements was also very good. Thus, this fault has finally been resolved.