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SM331 13 Bit Current to Analog Input Input

Created by: wmamangun at: 12/1/2011 3:12 AM (7 Replies)

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12/1/2011 3:12 AM	Rate (0)
wmamangun Posts: 4 Rating: (0)	Hi, i have a board that converts digital output to analog (DAC but only resistor in series powered by 24 VDC to get some mA reading) and want the PLC to read in current (mA) from 04 to 20mA. Without the PLC the output of my board is accurated with respct to what I really intend to get using a loop calibrator or mulitimeter. But whenever i connect the PLC, the reading is almost nothing, check the reading of the PLC also almost nothing. Please advise on what is the best setting/configutration for my PLC so that I can get the actual value that I need to get. Thank you. hope to hear anything that can help me out on this.
wmamangun Posts: 4 Rating: (0)	Last edited by: wmamangun at: 12/2/2011 10:20 AM
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12/1/2011 4:20 AM	Rate (1)
Navnag Platinum Member Joined: 11/21/2007 Last visit: 10/3/2023 Posts: 2321 Rating: (305)	Hello The Module Specifications of SM331 specifies that the the ( M- ) connections of various Voltage / current signals should be connected together. ( Pl see attached Data Sheet ) Practically also I have seen that reliable and accurate measurement is only achieved when M- of analog signals is at the same level. Therefore I think that you need to modify the circuit so that all resistances are on L+ side only and M- is directly connected to the 0V. Also all 0V ( M- ) should be connected to each other. Hope this helps Cheers Navnag Attachment S7300_AI_331_Module.pdf (100 Downloads)
	There is no such thing as the last bug in a program There are no stubborn bugs, There are only stubborn Debuggers.
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12/1/2011 7:30 AM	Rate (0)
wmamangun Posts: 4 Rating: (0)	Thanks for your fast reply. Meaning, all the channels M- terminals will be connected to each other?
wmamangun Posts: 4 Rating: (0)
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12/1/2011 11:39 AM	Rate (0)
Navnag Platinum Member Joined: 11/21/2007 Last visit: 10/3/2023 Posts: 2321 Rating: (305)	Well ... Theoretically ... There should not be a difference of > 2V between any two M- terminals. Practically .. it means that all M- terminals should be shorted to each other. Cheers Navnag
	There is no such thing as the last bug in a program There are no stubborn bugs, There are only stubborn Debuggers.
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12/1/2011 12:10 PM	Rate (0)
wmamangun Posts: 4 Rating: (0)	I have tried that settings but when 1 channel alarm, all the other channels are the same, alarm as well and the value that i get are all the same. is the PLC connection on the drawing i have provided correct?1 circuit like that corresponds to 1 channel, so basically I have 16 of that because I have 16 channels. But if I try to force alarm channel 2, all the channels give the same input value on my block. how can I isolate each channel of the PLC? Because it seems that each channel of the PLC is not isolated? Please enlighten me with this issue. Thank you very much. Appreciate your help.
wmamangun Posts: 4 Rating: (0)
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12/1/2011 12:40 PM	Rate (0)
Navnag Platinum Member Joined: 11/21/2007 Last visit: 10/3/2023 Posts: 2321 Rating: (305)	You are right. There is NO isolation between channels. ( Pl see Datasheet ). Also ( I believe ), that the mA in internally converted to a voltage signal ( measured across a load resistor ) and then fed to teh A->D convertor. Therefore if -ve pins of all Channels are not connected directly to the same ground potential ( 0V of 24V DC. ) then channels can affect each other. Also i have sometimes observed that if the mA signal is not a "Clean" DC signal ( due to high AC inteference signal superimposition, use of non Screened cable, non earthing of Cable screenetc. ) can also lead to erroneous measumements. Hope this helps Navnag
	There is no such thing as the last bug in a program There are no stubborn bugs, There are only stubborn Debuggers.
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12/2/2011 10:18 AM	Rate (0)
wmamangun Posts: 4 Rating: (0)	Hi Navnag, Thank you very much, the issue has been settled. M- will be connected to the -V of the supply. Thanks alot for your ideas it helps me alot.
wmamangun Posts: 4 Rating: (0)
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12/4/2011 11:14 AM	Rate (0)
Navnag Platinum Member Joined: 11/21/2007 Last visit: 10/3/2023 Posts: 2321 Rating: (305)	You are welcome !! Cheers Navnag
	There is no such thing as the last bug in a program There are no stubborn bugs, There are only stubborn Debuggers.
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