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# 1 analog signal for 2 analog module

## 3 posts in this topic

Dear Mr/Ms, I have an ultrasonic sensor with 4-20mA analog signal output. But I have 2 control panel with 2 PLC separate, two PLC have analog input module . Can I send signal for 2 analog module of 2 PLC with one sensor? If can how can I make them - Analog signal will connect analog (+) and analog (-)with module analog of 1st PLC and then from that terminal (analog terminal of 1st PLC) wiring to analog (+) and analog (-) of 2nd PLC ? or - Analog signal from sensor (+) will connect with (+) analog 1st PLC then (-) analog of 1st PLC will connect with (+) of 2nd PLC then (-) 2nd PLC will connect with (-) sensor ? or - Analog signal from sensor (+) will connect with (-) analog 1st PLC then (+) analog of 1st PLC will connect with (-) of 2nd PLC then (+) 2nd PLC will connect with (-) sensor ? Would you please help me to solve this? Thanks & best regards,

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It depends a bit on which PLC and which analog module you have but it can be done. Some modules have a switch for current loop while others have separate terminals. What you are suggesting won't work properly because the 4-20ma signal relies on a fixed 250 ohm resistance within the module. Two modules in series will double the resistance so the result may not be correct dependent on the sensor. The 4-20ma input signals work by measuring a 1-5 volt signal across a 250 ohm resistor. 1 volt = 4 ma, 5 volts = 20ma. You could do this by connecting the two input modules in parallel and setting one as current loop and the other as 1-5vdc, but this would make your circuit dependent on the module set as current loop to work. I suggest that you connect an external 250 ohm precision resistor between the sensor input and DC common. You can then set both modules up as 1-5vdc and measure the voltage across the 250 ohm resistor which will give you the same reading as a normal 4-20ma input.

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Dear Mr, Thanks for your help. Best regards,