Start and stop of the pump
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This post was last edited by zhoudingshengs on 2023-11-13 at 16:14. Discussion topics: 1. To stop the control pump via DCS, set up a passive normally open contact on the DCS; the contact of the intermediate relay should be NO, while the contact in the MCC control circuit should be NC. When the DCS soft button is pressed, the coil of the intermediate relay becomes energized, causing its contacts to close; this in turn opens the contacts in the MCC control circuit, thereby stopping the pump. In the DCS, once this passive normally open contact is closed, how can it be opened? 2. Control the start of the pump via the DCS: set a passive normally open contact on the DCS, with the contacts of the intermediate relay being NO as well as those in the MCC control circuit. When the DCS soft button is pressed, the coil of the intermediate relay becomes energized, causing its contacts to close; this in turn causes the contacts in the MCC control circuit to close, and the pump starts up. In the DCS, once this passive normally open contact is closed, how can it be opened?
1. After the passive normally open contact on the DCS closes, it can be opened by other signals or conditions. For example, when the pump stops operating, a certain time delay can be set before the contacts are opened, or the opening of the contacts can be triggered by signals from other devices or sensors. 2. After the passive normally open contact on the DCS closes, it can also be opened by other signals or conditions. For example, after the pump starts, it is possible to set a certain operating time before opening the contacts, or the opening of the contacts can be triggered by signals from other devices or sensors. .
1. The DCS soft button is set to “instant cut-off”: pressing the left mouse button sets it to “0”, while releasing it sets it to “1”“； 2. The auxiliary contacts of the contactor disconnect after the motor stops. 2. The DCS soft button is set to \"instantaneous on\": pressing the left mouse button sets it to \"1\", while releasing it sets it to \"0\"“ ； After the motor starts, the auxiliary contact of the contactor closes for self-locking.
For the DCS soft button output configuration, a pulse signal is sufficient
Typically, the start/stop signals for DCS are designed as pulse signals, meaning they automatically reset after being output for a certain period of time.
To control the pump, if it operates with single-point start/stop, use a continuous signal to turn it on and off. If it is about starting and stopping, with just two states, the signal should be provided as a pulse output; on the electrical side, starting generally involves self-locking.
This post was last edited by sun_fm on 2023-9-14 08:44. 1. For the selection of normally open or normally closed circuits for starting and stopping DCS, reference can be made to the electrical control panel; generally, the start circuit on such a panel is normally open while the stop circuit is normally closed. For consistency, instruments are also set up in this manner. 2. The DCS start/stop can be in pulse mode or hold mode. Under normal circumstances, the start, stop, and allow-to-start signals should be handled by the electrical department through a holding circuit. If the control contacts issued by the automation department require self-holding on the electrical side, design requirements should be submitted to the electrical department (the default is a pulse) ； 3. Whether DCS start/stop is controlled by 2 signals or 1 signal needs to be determined based on process operation or interlock requirements as well as the electrical control schematic; it is best for the process (including safety), electrical, and instrumentation teams to confirm this together ； 4. After clarifying the above points, let’s take a look at the problem again; it becomes clear once we use the schematic diagram of a certain control circuit
I don’t know why the image is black; let’s try uploading it as an attachment and see