Issue with setting the current alarm value for the mixer in the reactor in DCS
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For the JX300 DCS from Zhejiang University Zhongkong, an upper limit is set for the current alarm related to the mixer; however, the starting current of the motor is higher than this upper limit. How can this starting current alarm be suppressed?
This issue is quite common in DCS systems; the starting current can indeed trigger alarms mistakenly. It is recommended to try the following methods: enable the delay function in the alarm settings of the JX300; generally, a delay of 5–10 seconds is sufficient to avoid the peak starting current. If the system allows it, it is possible to set up a separate alarm suppression period for the mixer during its startup phase. The most reliable approach is to add a condition check for completion of startup in the program, using this condition as the basis for enabling alarms. We have also encountered similar situations in our workshop, and we resolved them by using the delay method. However, the specific parameters still need to be adjusted according to the motor’s characteristics; you can try setting the delay to a longer value first to see the effect.
Interlock not activated; it will be turned on once normal conditions are restored
The optical alarm provides a warning but no interlock function, so no action is required
I have added a 5-second rise-edge delay trigger to the interlock. The current issue is related to alarms; when an alarm occurs in the process area, it needs to be recorded along with the reasons and corrective actions. Therefore, I would like to know how to disable these alarms. In the I/O configuration alarms, a delay of 5 seconds was set for positive deviation alarms; however, there is concern that this might affect the normal alarms. The normal current is 4A, while the starting current ranges from 20 to 30A. The interlock threshold for high currents is set at 12A
Create local variables of type BYTE to serve as timers, such as JS1. The variable indicating the motor’s operating status is P1_RUN; the variable for the motor’s current value is P1_CURRENT. The following program should be written in the text function block: IF P1_RUN THEN JS1=JS1+1; END_IF; IF JS1>=100 THEN JS1=100; END_IF; IF JS1>10 AND P1_CURRENT>specified current value THEN P1_ALARM=ON; ELSE P1_ALARM=OFF; END_IF; IF P1_RUN=OFF THEN JS1=0; END_IF;
P1_ALARM is a custom variable; it serves as a BAOJING variable. When BAOJING is enabled, it is set to ON
Add a soft starter to the motor; if you have no money problems, you can also add an inverter.