How does DCS start and stop pumps, and how does it indicate pump faults and operating status?
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How does DCS start and stop pumps, and how does it indicate pump faults and operating status? Please explain using a typical design scenario as an example, thank you. For example: 1. The DCS sends a \"1\" signal to start the pump; should the relay in the DCS be connected in NO or NC mode (where NO means it is open when not powered)? And should the relay on the MCC side be connected in NO or NC mode (with NO meaning it is open when not powered)? Is this pump-starting signal from the DCS considered active at this point? Passive? Dry contact? Wet contact? 2. The DCS sends a “0” signal to stop the pump; should the DCS relay be connected in NO or NC configuration (where NO means it is open when not powered)? And should the relay on the MCC side be connected in NO or NC configuration (with NO meaning it is open when not powered)? Is this pump-shutdown signal from the DCS considered active at this point? Passive? Dry contact? Wet contact? 3. The DCS receives the pump failure signals sent from the MCC. Should the relay in the DCS be set to NO or NC (where NO means it is open when not powered)? And should the relay on the MCC side be set to NO or NC (with NO meaning it is open when not powered)? Is this pump fault signal of the DCS considered active at this time? Passive? Dry contact? Wet contact? 4. The DCS receives the pump operation signal sent from the MCC. Should the relay in the DCS be set to NO or NC (where NO means it is open when not powered)? And should the relay on the MCC side be set to NO or NC (with NO meaning it is open when not powered)? Is the operation signal for this DCS pump considered active at this time? Passive? Dry contact? Wet contact?
1 Startup: The DCS relay is set to NO and connected in parallel with the startup button on the MCC side; since the circuit is live, it isn’t a dry contact. The terms \"active\" or \"passive\" are not appropriate in this context, as they aren’t suitable for such situations. Nowadays, pulses are commonly used to start pumps. 2 Stop: The DCS relay is connected to NC and is connected in series with the stop button on the MCC side; the circuit is also live, and pump shutdown is also mostly achieved via pulses. 3 The fault signals and operation signals transmitted from the electrical system are dry contacts; however, a power supply is required on the DCS side to form a circuit that powers the relay coil, thereby causing the contacts to operate. The above applies to low-voltage motors; it is said that high-voltage motors have different starting and stopping methods, which needs to be verified.
The relay on the KA card does not have NO or NC contacts; it only has input and output terminals. Both starting and stopping functions are implemented through outputs, while the operation signal is an input. The relay itself is passive, with power coming from the terminals connected to the buttons.
Could you illustrate it with a diagram? Starting from the DO card in the DCS, to the relays in the DCS, then to the relays in the cabinets at the MCC, and finally to the motors on site. @ssln123
Each case needs to be analyzed on its own; as long as the function can be achieved and safety is ensured, that’s sufficient!