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Analog Input Raw Value Fluctuation in S7200

1/17/2009 9:16 AM	Rate (0)
Nil96 Posts: 325 Rating: (14)	Hi, The following problem have been noticed in recent projects which we have executed using S7200 PLC. We have been using 226CPU along with EM235(4AI/1AO) and EM231(4AI) for quite a number of projects. What wehave noticed during is that, say we have given constant 16mA to one of the Analog Input channel of EM235. In this case the Raw Count should be constant at 25600. But very frequently this number changes by + or - 1500 to 2000 counts. We also changed the4 to 20mA souce & this is not working even the source is set to some constant value. The same is noticed even with EM231 Analog Input Cards. We tried changing the Analog Filter settings. But this is not working. Need some help............. Regards Nil
Nil96 Posts: 325 Rating: (14)
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1/19/2009 6:49 AM	Rate (0)
Nil96 Posts: 325 Rating: (14)	Hi, Further to the post which I sent earlier, please make a note that we have taken godd care of ground & earth. Regards Nil
Nil96 Posts: 325 Rating: (14)
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3/31/2012 8:47 PM	Rate (0)
Kareem Elharony Posts: 6 Rating: (0)	I 'm facing the exact problem right now, We're injecting current to the Analog input module with fixed value but the value is fluctating in cpu as well as the corresponding bar on HMI ? What could be the reason for such problem ?
Kareem Elharony Posts: 6 Rating: (0)
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7/3/2012 8:33 AM	Rate (0)
zaym35 Posts: 2 Rating: (0)	facing the same problem in the area....can anyone clarify this?
zaym35 Posts: 2 Rating: (0)
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7/3/2012 9:05 AM	Rate (0)
Marcjan Diamond Member Joined: 4/22/2010 Last visit: 3/31/2025 Posts: 5697 Rating: (716)	Hello, Can you give us the specifications off the Sensor connected to the module and how the powersupply connections are made? Are Sensor, CPU and EM on same supply? Regards, Marcjan
	Problem solved? Please let us know! Please no technical questions by PM, use the forum sections for your questions.
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7/3/2012 9:25 AM	Rate (0)
zaym35 Posts: 2 Rating: (0)	Actually the input just a output from digital meter. Yup , all power supply from same source. Wiring all correct according from manual. Just found out just now , removing the deadband from input filter at system block the value stable alot. actually quite accurate. Thanks for the reply and help thanks....
zaym35 Posts: 2 Rating: (0)
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7/3/2012 8:28 PM	Rate (0)
anilplc Experienced Member Joined: 11/30/2007 Last visit: 7/2/2025 Posts: 23 Rating: (0)	Hi, Please do proper earthing and use shielded cable for analog signals, put one round magnet on analog signal wire.

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5/9/2013 10:09 AM	Rate (0)
Er. Sanjay Mistry Posts: 79 Rating: (7)	First of all, online with a blank PLC, just monitor the values of analog input. Connect any 1 analog input & check wether it is varying? The main reason of the problem ib noise & earthing i.e. grounding error. 2nd thing, keep CPU away from noise generation equipments like drives & motors.
Er. Sanjay Mistry Posts: 79 Rating: (7)
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