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4 - 20mA AI Issue

Created by: carson218 at: 6/28/2010 5:49 PM (7 Replies)

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6/28/2010 5:49 PM	Rate (0)
carson218 Posts: 7 Rating: (0)	Hi, I am unable to get 4 - 20mA inputs to work with my system, I am using a CPU 1214C AC/DC/Rly with a SM1231 AI4 card. I get the following readings from the AI card when using a watch table for the analogue AI's; Address Display Format Monitor Value %IW96 DEC_Signed-16768 transmitter connected (when meter put over terminals reading correct polarity/mA reading) %IW98 DEC_Signed759 nothing connected (empty terminals) %IW100 DEC_Signed -16768 nothing connected (empty terminals) %IW102 DEC_Signed 5310/6827 (signal fluctates) nothing connected (empty terminals) This is the second card I have tried and similar results. I have wired the inputs as per FAQ for 2 wire transmitters. I have also tried using a Unomat to connect direct to the AI but still no joy. Any help would be appreciated. Nicky.
carson218 Posts: 7 Rating: (0)
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6/29/2010 1:33 AM	Rate (0)
Flomaster Posts: 65 Rating: (2)	Hi! I'm not expert in such questions, but I suggest you to check connections of sensors to your analog signal module (use Wiring diagrams of S7-1200 system manual). Also check the type of signal for AI in STEP7 (PLC - Device configuration). Select your analog module at this page and look at Properties tab. The measurement type of each AI pair may be Current or Voltage. Set required type there. Good luck! P.S. I think, the problem is in incorrect connection.
Flomaster Posts: 65 Rating: (2)	Last edited by: Flomaster at: 6/29/2010 1:34 AM
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6/29/2010 12:31 PM	Rate (0)
Denilson Pegaia Platinum Expert Joined: 9/23/2005 Last visit: 2/2/2023 Posts: 4177 Rating: (1324)	Hi, check if your sensor is active (4 wire) or passive (2 wire). Check also if all - inputs are interconnected with M and if necessary with the earth.
	Denilson Pegaia Siemens Industry Sector Technical Support
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6/29/2010 6:26 PM	Rate (0)
carson218 Posts: 7 Rating: (0)	Hi, The transmitters I am connecting are 2 wire passive. I have double checked the wiring with colleagues and I am confident they are ok. I have bypassed the Siemens AI card and wired the 4-20mA to a datalogger and it reads the 4-20mA signal ok. Hardware configuration is set at 0-20mA, no errors in diagnostics - not sure about readings at watch table for IO, doesnt appear to be consistent for the channels yet similar figures when I tried a similar card???? Any further help would be appreciated. Nicky
carson218 Posts: 7 Rating: (0)
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6/29/2010 7:00 PM	Rate (0)
Denilson Pegaia Platinum Expert Joined: 9/23/2005 Last visit: 2/2/2023 Posts: 4177 Rating: (1324)	Hi, check if the wiring is like the follow picture Attachment 2wire.JPG (934 Downloads)
	Denilson Pegaia Siemens Industry Sector Technical Support
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6/30/2010 10:19 AM	Rate (0)
carson218 Posts: 7 Rating: (0)	Hi Pegaia, Please can you advise if the diagram shows shunt resistors, if so what value? Thanks, Nicky.
carson218 Posts: 7 Rating: (0)
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7/1/2010 1:06 PM	Rate (0)
Denilson Pegaia Platinum Expert Joined: 9/23/2005 Last visit: 2/2/2023 Posts: 4177 Rating: (1324)	Hi, 10V / 20 mA = 500 ohms
	Denilson Pegaia Siemens Industry Sector Technical Support
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3/6/2013 3:16 PM	Rate (0)
Danath Posts: 11 Rating: (1)	You should not need a shunt resistor the analog module does that for you if you change the properties on the analogmodul to "current" in the configuration in TIA portal Here are correct wire diagrams https://support.automation.siemens.com/CN/llisapi.dll?func=cslib.csinfo&objId=40914972&nodeid0=10805065&nav0=index&load=treecontent&lang=en&siteid=cseus&aktprim=0&objaction=csview&extranet=standard&viewreg=CN
Danath Posts: 11 Rating: (1)	Last edited by: Danath at: 3/6/2013 3:17 PM
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