Interlocking problem
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The feed pump of the existing unit is located within 500 meters of the control room, and the SIS interlock system is used to shut down this pump in case of an emergency. Due to planning changes in the facility, the raw material storage tanks need to be moved from their current locations, and the feed pump as well. After being moved, the pump will be approximately 2000 meters away from the DCS control cabinet room. The management is concerned that such a long distance might affect the functionality of the interlock system. Do any of you have any good suggestions? Thank you very much
What is the relationship between line length and interlocking? That doesn’t make any sense
There are good solutions. Just make your boss shut his worries up – that’s it. :Lol, those idiots are causing trouble for no reason; what a waste of time...........
The transmission of signals weakens as distance increases, but these weaknesses can be addressed, so distance does not pose a problem.
Are your pumps directly controlled by the SIS? The pump’s start/stop operation relies on a 220V circuit; shouldn’t it be controlled by a relay in the control room?
In interlock control circuits, digital signals generally experience little attenuation. Moreover, interlocks are used to control the distribution room, and this is unrelated to the distance of the equipment
It was suggested upstairs that instead of the SIS controlling the pumps on-site directly, it should go to the power distribution room. Unless an emergency stop button is also installed on-site and linked to other interlocks?
The 2000-meter switch signal is unaffected.
The SIS relays in our factory are not connected to passive digital switches; rather, they have a 220V power supply. The operations of starting and stopping the pump involve this 220V power supply as well. Therefore, after the location of the pump was changed, the wiring length increased by over 1,000 meters, and we are concerned about voltage drop due to the 220V supply
Even at 220V, it is the relay in the pump’s secondary circuit that is controlled by the power supply; the relay operates at just a few volts. Calculate the voltage drop along the cable over a distance of 2000 meters, as well as the minimum operating voltage required for the relay – then there will be no problems. 2000 meters isn’t a problem at all.
For long-distance AC control circuits, it is necessary to take into account not only voltage drop but also circuit capacitance, which can prevent AC contactors and relays from releasing. For more details, refer to pages P1105–P1106 of the fourth edition of the Industrial and Civil Power Supply and Distribution Design Manual, where Table 12.1–13 presents the reference values for the critical length of AC control circuits based on critical capacitance, as well as the maximum reference values for control circuits determined by voltage drop