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Problem with analog input

Created by: D_M_D at: 6/18/2010 8:16 AM (9 Replies)

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6/18/2010 8:16 AM	Rate (0)
D_M_D Posts: 11 Rating: (0)	Dear experts, I have an analog input module 2xAI/12 bit with ref. 6ES7 331-7KB02-0AB0 (the CPU is 315-2 DP). The channel is configured for voltage measurement +/-10V. On the first input I have a signal 7.2V which comes from a temperature regulator Eurotherm. On the other analog input there is a signal 3.3V comming from Pt100 with transmitter. The problem is that recently I cannot see the two inputs togather. If I unplug the second input I am able to see the value on the first input. When I plug them back to their terminals I see a value only at the second input, and on the first there is an error value 32767. I have checked the electrical connections and they seems to be ok. I have also replaced the analog module with new one and it seemed to be ok. However, two hours after the replacement the situation was as it was before - only second input has a value. The problem is that this instalation has been working for more than one year without this type of anomaly. Have you ever had this kind of problem? Do you have any piece of advice what could be the reason and how to solve it? Thanks!
D_M_D Posts: 11 Rating: (0)	Last edited by: D_M_D at: 6/18/2010 8:17 AM
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6/18/2010 8:59 AM	Rate (0)
Darius Platinum Expert Joined: 9/28/2005 Last visit: 8/27/2024 Posts: 2957 Rating: (242)	Hello, Did you measured voltage with multimeter (calibrated and accurate) on both channels when problem persists ? What it shows ?
	Best regards, Darius
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6/18/2010 9:22 AM	Rate (0)
Ayman Elotaify Platinum Expert Joined: 5/28/2008 Last visit: 9/9/2024 Posts: 4515 Rating: (839)	Hello D_M_D, Please check that the AI signal cables are shield cables and check that you have grounded them. Please check SIMATIC S7-300 S7-300 Module data. Check that pins 3, 5, 11 & 20 are connected together. refer to page 323 in section 6.8 of the module data. Also check that the measureing range module (in the side of the module) is set to position B Regards,
	Last edited by: Ayman Elotaify at: 6/18/2010 9:36 AM Ayman Elotaify
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6/18/2010 10:28 AM	Rate (0)
D_M_D Posts: 11 Rating: (0)	Darius Hello, Did you measured voltage with multimeter (calibrated and accurate) on both channels when problem persists ? What it shows ? The multimeter shows 7.2V on the first channel and 3.3V on the second.
D_M_D Posts: 11 Rating: (0)	Last edited by: D_M_D at: 6/18/2010 10:30 AM
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6/18/2010 10:30 AM	Rate (0)
D_M_D Posts: 11 Rating: (0)	Ayman Elotaify Hello D_M_D, Please check that the AI signal cables are shield cables and check that you have grounded them. Please check SIMATIC S7-300 S7-300 Module data. Check that pins 3, 5, 11 & 20 are connected together. refer to page 323 in section 6.8 of the module data. Also check that the measureing range module (in the side of the module) is set to position B Regards, I haven't checked the pins but I'm pretty sure they aren't conected togather. Thank you for the guidance.
D_M_D Posts: 11 Rating: (0)
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6/18/2010 10:36 AM	Rate (0)
Darius Platinum Expert Joined: 9/28/2005 Last visit: 8/27/2024 Posts: 2957 Rating: (242)	Hello, Is it possible that one of the inputs ir burned or it is only not working that both are connected ?
	Best regards, Darius
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6/18/2010 11:13 AM	Rate (0)
D_M_D Posts: 11 Rating: (0)	The first one in not working when they are both connected. When I disconnect the second input, the first one goes ok. And all the time there is no SF either on the AI module, nor on the CPU.
D_M_D Posts: 11 Rating: (0)
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6/18/2010 11:27 AM	Rate (0)
UMENCHO Diamond Member Joined: 3/21/2006 Last visit: 9/10/2024 Posts: 10228 Rating: (1181)	Hello, Did you try with changing the inputs, means on first connect PT100 analog transmitter and on second input connect regulator? Is it possible to change the PT100 transmitter and cable? My opinion is - in it should have some problem. You already mentioned that you checked connections and cables but... Best regards, Hristo Mihalev

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6/18/2010 12:35 PM	Rate (0)
Darius Platinum Expert Joined: 9/28/2005 Last visit: 8/27/2024 Posts: 2957 Rating: (242)	Hello, Download this manual and check voltage measuring connection diagram for your module. Two channels are connected in groups and I think (and this is only mine oppinion) that your connected devices can be broken or something and in that case you burned one of the inputs of AI module. Its is possible because as you said new module works ok for several hours and then it never works ok after that. It is definitely damaged and I think its damaged due to problems in connected devices or cables.
	Best regards, Darius
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6/18/2010 1:20 PM	Rate (0)
Aret Posts: 2348 Rating: (264)	My bet - the problem is grounding/different power supplies. :^) To check this you need to make galvanic isolation between them - for ex. we use one from Phoenix Contact for this purpose. Also try to go online in HWKonfig when both sensors are connected and see if there is something in module properties and Diagnistic buffer of CPU. Upd.2 D_M_D can you put wiring diagramm including power lines here?
Aret Posts: 2348 Rating: (264)	Last edited by: Aret at: 6/18/2010 1:25 PM Last edited by: Aret at: 6/18/2010 1:24 PM
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