The Sparky Posted December 22, 2011 Report Share Posted December 22, 2011 I need to run a signal from a pressure transducer ( 4-20mA ) over a 300m distance before it gets to the analog input on the OPLC. Is this distance too long? At the moment the transducer supplys an input for a different PLC which is located near the transducer. Can I parallel off this input and run the signal to my V570-57-T20B 300m away ? If its a matter of using the right size cable then what size would suite ? Link to comment Share on other sites More sharing options...
MVP 2023 Joe Tauser Posted December 23, 2011 MVP 2023 Report Share Posted December 23, 2011 You should have no problem running a 4-20 mA signal 300 meters- the voltage drop will be very small and you can ignore it. The problem may by in the other PLC you are connecting to. If the 4-20 input on that PLC is isolated, it will work. Unitronics connects the negative of the analog inputs to the power supply negative (non-isolated), so if your other PLC is non-isolated the signal will end there. You will probably need a loop isolator between the two. Joe T. Link to comment Share on other sites More sharing options...
Emil Posted December 25, 2011 Report Share Posted December 25, 2011 Take care of the noise too. Use relaivelly thick (low resistance), shielded twisted pair. Be sure you connect the shield in one side only to a good grounding point or to 0V of 24v power supply. Check which connection gives you better result. Link to comment Share on other sites More sharing options...
Gabriel Franco Posted December 29, 2011 Report Share Posted December 29, 2011 I´ve wired series circuit two devices (PLC and local display) to a single transmitter up to 100 m without trouble. Parallel has not worked for me: it´s not repetitive and not linear at whole range. Link to comment Share on other sites More sharing options...
The Sparky Posted January 17, 2012 Author Report Share Posted January 17, 2012 You should have no problem running a 4-20 mA signal 300 meters- the voltage drop will be very small and you can ignore it. The problem may by in the other PLC you are connecting to. If the 4-20 input on that PLC is isolated, it will work. Unitronics connects the negative of the analog inputs to the power supply negative (non-isolated), so if your other PLC is non-isolated the signal will end there. You will probably need a loop isolator between the two. Joe T. You were saying that unitronics dont have an isolated analog input. The specs on the v200-18-e3xb snap in i/o say that it has 4 isolated analog inputs, is this ok? Link to comment Share on other sites More sharing options...
MVP 2014 Simon Posted January 17, 2012 MVP 2014 Report Share Posted January 17, 2012 Hi, OK, now this prompts me to read the instructions over again and get out the mulitmeter... On the E3XB, the inputs are isolated from other signals and power supply, but not from each other (they share a common). So if you are using only one input then you can consider the input fully isolated. However if you are using other inputs, you need to consider whether any of those circuits forms a connection between the analogue common and the overall system/chassis ground. If the anser to this is "yes" then the isolation is defeated. Link to comment Share on other sites More sharing options...
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