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Analog Input unstable

Created by: Gordon at: 9/9/2008 7:22 PM (8 Replies)

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9 Entries

9/9/2008 7:22 PM	Rate (0)
Gordon Posts: 4 Rating: (0)	I am having aproblem with an analog it is being unstable, if i apply 5v the input string i reading backwards and forwards from 0 17000. It should be 17000 at all times and is triggering an alarm in my program. I have checked the dip switches 1 & 3 is on the rest is off. Can anyone help
Gordon Posts: 4 Rating: (0)
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9/9/2008 8:00 PM	Rate (2)
Gebhardt Karl Posts: 1502 Rating: (176)	How often do you read ? Look, each Input needs Time to "Read-IN" . If you read to fast, the the Alaog-Input say "0". Read information how time need for read inputs. (Time is in ms) Try read every 1 Second. I think it is O.K. For faster you must read Card-Spezifikation.
Gebhardt Karl Posts: 1502 Rating: (176)
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9/10/2008 3:53 AM	Rate (1)
marcsinclair Posts: 49 Rating: (5)	Analogue inputs can be troublesome. If you are sure that the voltage is stable (no superimposed hum, pay attention to earthing, cable type etc.) then you should use input filters. There is a built in analogue filter in the system block, using this you can average inputs upto 256 samples and adjust the deadband. You should read the help file associated with this feature, it is detailed and thorough. Regards
marcsinclair Posts: 49 Rating: (5)
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9/10/2008 8:34 AM	Rate (0)
Helmut_13 Posts: 2930 Rating: (432)	Hi, here adiitional notes to marcsinclairs post: 1. Unused analog inputs must be short-circuit. 2. Use shilded wires for your analoge sensor, grounding only at one side 3. Check if your analoge wiring is in parallel to high voltage/current wires. If so, change it Do you have ASi-Master, or SIWAREX modul connected to S7-200? If so, then use the right analoge chanel because this two modules use analoge I/Q to communicate to the PLC. Here an older but still actual FAQ from Siemens: http://support.automation.siemens.com/WW/view/en/2415890 I hope this helps. Helmut
Helmut_13 Posts: 2930 Rating: (432)
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9/10/2008 9:39 AM	Rate (0)
Khaled_Ezzat Gold Member Joined: 9/7/2007 Last visit: 4/3/2025 Posts: 550 Rating: (62)	Hi Gordon, I faced this problem once ago and I connected the shield the M and the result was good
	Best Regards
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9/10/2008 12:14 PM	Rate (0)
AMAZINGAHMED Posts: 719 Rating: (88)	Please take care that when you're connecting the shield to M, then connect it from one side (from the control cabinet side). It happened to me too before and connecting the shield to M succeeded. But I don't know the technical reason for this.
AMAZINGAHMED Posts: 719 Rating: (88)
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9/16/2008 11:51 AM	Rate (0)
Ayman Elotaify Diamond Expert Joined: 5/28/2008 Last visit: 1/14/2026 Posts: 4522 Rating: (843)	Iam Agree with Khaled and AmazingAhmad. You can connect the shield to M and I expect that this will solve your problem. Please tell me do you have more than one power supply in your system? (i.e. power supply for PLC and others for field?) If yes, thentry to make all power supplies having the same reference. And all the ground of the power supplies should be connecected to each others and should also connected to the ground of the machine. Try to make this solution in the begining before connecting the shield to (M).
	Last edited by: Ayman Elotaify at: 9/16/2008 11:52 AM Ayman Elotaify
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1/25/2010 11:14 AM	Rate (0)
Preeja P. Posts: 2 Rating: (0)	I faced this problem too, hope this way can solve mine.
Preeja P. Posts: 2 Rating: (0)
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1/26/2010 3:17 AM	Rate (0)
fqiang Posts: 23 Rating: (0)	I prefer using currentsignal to voltage signal ,because of impedance in long distance. Fllowing solution Above ,if it can not be solved , you can try using converter. it's my opinion.
fqiang Posts: 23 Rating: (0)
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