Greetings everyone, I am currently in the process of connecting a Digital Output (DO) signal from one programmable logic controller (PLC) to the Digital Input (DI) card of another PLC. To achieve this, I have integrated a dry contact relay with the DO output. However, I have encountered a problem where the voltage received at the second PLC's DI card is only 1.5V, despite using a 24V power supply from the initiating PLC. Would it be more effective to utilize the 24V power supply from the receiving PLC's panel to energize the relay instead? Subsequently, the relay output would be connected to the DI card of the receiving PLC. Any advice or recommendations on this matter would be highly valued. Thank you in advance for your assistance.
Connect the output of the First PLC to the Relay's Coil using the appropriate voltage from the output module and the common terminal of the first PLC for A1 and A2 connections. Link the input of the Second PLC to the Relay's Normally Open (N.O.) contact, utilizing the Second PLC's power source for the other side of the N.O. contact. Position the Relay within the First PLC's panel to ensure that the output power and common connections remain localized. To distinguish wires carrying voltage and input from the Second PLC, use yellow wire to indicate the external power source to the First PLC's panel. This precaution is necessary to account for the presence of live voltage in the panel from the Second PLC even if all power to the First PLC is switched off.
As a dry contact, separate power sources are required for both the input and output to operate effectively. It appears that the input card on the second programmable logic controller (PLC) may not be supplying power. Refer to the manual for your input card to understand the proper way to connect power to the circuit.
Before proceeding with your electronic project, it is crucial to map out your circuit and track the path of the current flow. In every electronic device, the power supply needs to form a complete circuit from the positive to the negative terminal. When the relay is activated by the output of the first PLC, the coil requires a pathway back to the power supply. Additionally, for the relay to trigger an input on the second PLC, the contact must be powered by the voltage source connected to the second PLC's input card, which will also need a return pathway. Understanding and ensuring proper circuit connections is essential for optimal functionality of your electronic devices.
While your responses are insightful, I would like to share an anecdote from my previous workplace. We operated production lines with several machines, each running on its own 480V power supply that also powered a 120V control power transformer. These machines, such as PLC2 and PLC5, used 120VAC IO modules. In our setup, when connecting machines that required 3 signals, workers would use 3 red conductors to link the output to the input directly. The circuit would be completed through the Equipment Grounding Conductors (EGCs). However, the wires were not always color-coded as yellow, posing a safety risk. This method technically functioned but violated electrical codes. While we made efforts to rectify the issue, not all machines were updated. It is crucial to adhere to regulations that necessitate externally energized conductors to be colored yellow (or, as per current code, orange) and recommend using local power to energize relays. Signals transferred through dry contacts should derive power from the recipient machine's power supply for optimal safety and compliance.
I greatly appreciate everyone's assistance! Initially, I attempted to resolve the issue by connecting the 0V from both panels, which proved successful. However, ultimately I opted to implement the suggested solution, which worked seamlessly.
Hi there! From what I understand of your situation, I think your proposed solution sounds reasonable. Using the 24V power supply from the receiving PLC panel should maintain a higher voltage across your relay. This should, in turn, provide the adequate voltage you require at your DI card. However, I'd highly recommend that you double-check the ratings of your DI card: you need to ensure it can handle the increased voltage to prevent any potential damage. Always err on the side of caution when it comes to possible overvoltage situations. Hope this helps!
Hello! Yes, integrating the 24V power supply from the receiving PLC's panel should help. Your relay might only be providing a pass-through for the originating PLC's voltage signal, rather than stepping up the voltage. By using the receiving PLC's power supply, you're effectively ensuring that the relay is receiving the correct voltage to begin with. However, don't forget to verify the ratings of your relay and DI card to ensure they can handle the 24V supply without causing any damage.
It sounds like you're on the right track with diagnosing the issue! Using the 24V supply from the receiving PLC to energize the relay could definitely improve the voltage at the DI card. That way, you're ensuring that the relay is fully powered according to the specifications, which should help eliminate any voltage drop you’re experiencing. Just make sure to check the relay's specifications to confirm it can handle the current from the DI card. It could also be useful to double-check the wiring and connections to ensure there are no loose ends causing additional resistance. Good luck!
It sounds like you're on the right track by considering using the 24V power supply from the receiving PLC to energize the relay. This should eliminate any voltage drop issues you're facing since you'll be powering the relay directly from the same source as the DI card, allowing for a more reliable signal. Just make sure that the relay's output contacts are compatible with the input requirements of the DI card, and double-check your connections to ensure everything is wired correctly. Good luck, and I hope this resolves your issue!
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Answer: Answer: The voltage drop could be due to various factors such as resistance in the wiring or components. Troubleshooting these issues can help identify the root cause.
Answer: Answer: Utilizing the 24V power supply from the receiving PLC's panel can be a viable solution to address voltage issues and ensure compatibility between the two systems.
Answer: Answer: Integrating a dry contact relay as a buffer between the two systems can help isolate and protect the PLCs while ensuring proper signal transmission. Testing and verifying the connections are also essential steps in troubleshooting voltage discrepancies.
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