Hello Guys

       Maybe this is a stupid question, but I need to confirm. I am not an expert with PLC, and i never connected a 4 to 20mA signals to or from PLC. But for my recent project, i need to connect a pressure sensor which gives 4 to 20mA signal to PLC and take out 4 to 20mA from PLC to a E/P converter. So i have an analog module and i know that i have to configure and AI and AO as 4 to 20mA in device and config of TIA portal. But an other electrician in my company says that i have to connect a resistor in between the wires on input and output. Is it necessary to connect a resistor, in between AI+ and AI-. and between AO+ and AO-.... He says he is very sure, and if i ask why, he says it is to filter the noises... So I want to confirm with you experts.... I appreciate your inputs.... 

Hello,

              Kindly tel me the Part number of Your PLC And analog module MLFB Number .

             And you don't need to Connect Resistance and all . Because Module Itself have Inbuilt Filter . 

             So U have to connect Directly Sensor to Analog Module . And U Must have to Use Shield Cable for Analog Wiring For signal Losing , grounding the Analog Shield .

Regards,

Arasan.

Hello JAC2016,

Here is a link to manual:

SIMATIC S7 S7-1200 Programmable controller

See appendix A.10.3 for information about wiring the analog module

Best regards,

Wizard

JAC2016

Hello... The PLC is Siemens S7-1212C and Analog input/output module SM 1234 4AI/2AO module. I guess they connect the resistor if they want to convert current to voltage, and for current signal I believe we dont need a resistor.. But the electrician in my company said we have to put a resistor, and he said i know nothing.... so i have to ignore him and connect as you guys advice me to...  

 Hello ,

               Your Filed sensor Analog (voltage/Current) , You directly Connect to Plc  Analog Module - Shield cable.

              Analog Module Configuration you Have to select  ( Volt Or Current ) In Hardware Configuration.

             In my experiance I have used this this way . Then You decide your safety .

             Here i have enclosed the image of hardware Configuration for Analog ( Volt/Current).

Regards,

Arasan.

 Hello JAC

JAC2016

I guess they connect the resistor if they want to convert current to voltage, and for current signal I believe we dont need a resistor..

 Bingo!

JAC2016

But the electrician in my company said we have to put a resistor, and he said i know nothing...

That is a really shame that an electrician underestimate other collaborator. If there are doubts, so the better solution is to have a look in the manual. And the manual says what you has just said.

I think there are enough explanations given for the other mates here in the forum. Also, if your electrician keeps saying that need the resistor, ask him for an engineering explanatión (As far as I know, for filtering in DC, you need a capacitor... even is a normal practice in the microcontrollers use in some pins to decrease the noise)

Regards,

Javier

Hello,

I have seen people connecting a resistor to change a voltage value into a current value.

Maybe that is why your collegue suggest you to do that.

If the sensor provide 4-2mA, no need to add a resistor.

Best regards,

Hugo

dear find attach pic

no need to connect resister just follow as it is in connection.