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6ES7-331-7PF01-0AB0, value jump from 90 to 130 in 2-3 sec

Created by: Kargan at: 3/4/2014 1:21 PM (12 Replies)

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3/4/2014 1:21 PM	Rate (0)
Kargan Advanced Member Joined: 6/19/2008 Last visit: 6/1/2023 Posts: 46 Rating: (4)	Hi, I don't want to create new topic becasue more or less problem can be related to the same module. I have6ES7 331-7PF01-0AB0 and it behaviour is really strange... 6 PT100 sensors (4 wired) are installed in a stator of generator. Until generator is "out of a grid" everything is fine with measurements (temp. around 40 C) but in a moment when we are synchronized with a grid and generator reach around 100 MW few of those temperatures are getting to go crazy. One of channels show 130 C, one 90 C...and the value jump from 90 to 130 in 2-3 sec. It is not possible that real temperature in a stator "jumps" like that so it has to be something with module itself or somehow resistance of wires is "going to crazy" (electromagnetic disruption) ? Any ideas ?
	Last edited by: GrasserF at: 3/4/2014 1:35 PM neuer Beitrag nach den splitten von /tf/WW/en/Posts/33009 Last edited by: Kargan at: 3/4/2014 1:22 PM
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3/4/2014 2:38 PM	Rate (0)
Aret Posts: 2348 Rating: (262)	Of course temperature can't jump like this. And it seems like EM interference, though also you can get similar effect if one of wires in 3 wire scheme has unstable electrical connection and due to vibration it breaks. The thing you should do is to check grounding first of all.
Aret Posts: 2348 Rating: (262)
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3/4/2014 2:43 PM	Rate (0)
weddra37694 Posts: 6 Rating: (0)	Provide more information on the installation. What is the wire guage/size? How long are the leads from the sensor to the module? Please provide hardware configuration details (filtering mode, climatic/standard sensor range, etc...) and which channels are wired on the module? You state that there are 6 sensors connected. Which two channels are not connected, or are they used for other purposes? I need a complete picture of how the module is setup to understand why you get the wild reaction. And you are correct, it is possible that some kind of electrical disturbance could be energizing the wires going to the RTD, however, in a 4w connection, this usually cancels out if the wires are in a bundle.
weddra37694 Posts: 6 Rating: (0)
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3/4/2014 9:02 PM	Rate (0)
IBN-Service Posts: 8946 Rating: (996)	Shielding or equipotential seems to be not OK. Also possible, that wrong PT100 are installed.
IBN-Service Posts: 8946 Rating: (996)
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3/4/2014 9:05 PM	Rate (0)
IBN-Service Posts: 8946 Rating: (996)	weddra37694 ...And you are correct, it is possible that some kind of electrical disturbance could be energizing the wires going to the RTD, however, in a 4w connection, this usually cancels out if the wires are in a bundle. No, I dont agree. 4W is to compensate length of cable but not against EMI.
IBN-Service Posts: 8946 Rating: (996)
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3/4/2014 9:34 PM	Rate (0)
weddra37694 Posts: 6 Rating: (0)	You are correct about 4W compensating for cable length. However, if the wires are run together (twisted even better), the EMI noise is applied to all 4 cables. The input circuit for the RTD moduleis differential and the noise will be rejected as normal mode noise. If the cables are not run together, then you are 100% correct that the EMI will effect the inputs eratically.
weddra37694 Posts: 6 Rating: (0)
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3/4/2014 9:40 PM	Rate (0)
IBN-Service Posts: 8946 Rating: (996)	weddra37694 You are correct about 4W compensating for cable length. However, if the wires are run together (twisted even better), the EMI noise is applied to all 4 cables. The input circuit for the RTD moduleis differential and the noise will be rejected as normal mode noise. If the cables are not run together, then you are 100% correct that the EMI will effect the inputs eratically. No, I still dont think so. Because 2 wires are only for supply and 2 wires are only for probe. There is no differential readout, as far as I know. Do you have a link or something to explain your idea?
IBN-Service Posts: 8946 Rating: (996)
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3/4/2014 9:53 PM	Rate (0)
weddra37694 Posts: 6 Rating: (0)	Input circuit uses an AD623 instrumentation amplifier.
weddra37694 Posts: 6 Rating: (0)
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This contribution was helpful to 1 thankful Users IBN-Service

3/5/2014 1:44 PM	Rate (0)
Aret Posts: 2348 Rating: (262)	Generally i agree with weddra. He writes about an assumption that 2 wires, which are laying close to each other, have same reaction on EMI. Not relating to 4 wire RTD scheme we can tell, that if EMI causes potential growth at wire A of 1 volt and on wire B also 1V we can treat this as no EMI took place as we measure voltage = difference between wire A and wire B potential. Twisting wires in pairs just allows 2 wires to be even closer. Also i would ask thread starter to identify sensors used, because some PT100 sensors are isolated, others not.
Aret Posts: 2348 Rating: (262)
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5/9/2014 2:07 PM	Rate (0)
Ugljesa Bronze Member Joined: 10/29/2012 Last visit: 9/7/2023 Posts: 102 Rating: (1)	I had simillar problem on small generator. Check terminals. When generator goes on grid, we have vibrations and they can couse such problem. Best regards.

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