How far can a relay open-circuit signal be transmitted?
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Dear experts, I want to use the normally open signal from a relay to display the motor status on the DCS. How far can such a normally open signal be transmitted? Is 500 meters sufficient? Is the interference high? If auxiliary contacts of a contactor are used, how far can it transmit? I need the help of all experts! Thank you
The distance over which it can transmit data depends on the requirements regarding line resistance in the circuit; different circuits and signals result in different requirements, and it is also related to the gauge of the cable you choose. Check some information and do the calculations yourself. However, the longer the circuit, the more affected it is by interference; therefore, try to keep it as short as possible to avoid malfunction.
What does the dry contact of a relay refer to? If it refers to passive contacts, in my understanding there is no difference between them and the auxiliary contacts of a contactor. As for the transmission distance, it depends on the requirements of the DCS DI card for the signal (voltage, current) as well as the power consumption along the line; specific calculations are needed. If there is too much signal loss and the signal reaching the card is too weak, then it will not work.
500 meters is fine; there is little interference and the line resistance is very low
500 meters? Could you tell me about your situation? Generally, the status of the motor is monitored by taking readings from the contactors in the MCC cabinets. The MCC cabinets and DCS cabinets for a given area are usually located in the same control building
Without considering interference, the loop impedance can be calculated as long as it remains within the technical specifications of the DCS card； Taking interference into account, shielded cables can be selected, and during installation, they should be kept away from the power cables of high-power equipment as much as possible.
500 meters is no problem; I have worked on auxiliary equipment projects for power plants, and the PLC can read the signals correctly. In typical power plants, 4mm2 wires are used to transmit such signals. For example, the characteristic resistance of Siemens PLC cards is 250 ohms, and by checking the upper and lower current limits, the required settings can be determined – this is the standard design process.
Bro, your question is a bit silly. What does the distance it can be transmitted over have to do with the contacts? For this, it depends on the DCS source. :lol
You haven’t been to the scene, have you? There is usually a distance involved; once that distance is exceeded, interference occurs
500 meters is great; my company still uses it even at 1500 meters
Interference? Shielded cables are generally fine. If you’re really scared, just use a protocol and messaging.