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Problem with 3-wire transducer on analog input

Created by: Jens_app at: 8/14/2015 3:16 PM (15 Replies)

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8/14/2015 3:16 PM	Rate (0)
Jens_app Gold Member Joined: 1/5/2011 Last visit: 6/15/2024 Posts: 815 Rating: (121)	Hi, We are trying to connect a 3-wire transducer (4-20mA) to the analog input of a CPU313C. When we measure the output of the transducer, with a multimeter, we get 4mA as 0 value, which is good. But once we connect the transducer to the analog input card, the value drops to 2.6mA. We first thought it was a grounding error, but that doesn't seem to be the case. We have put the transducer and and PLC on a common ground. The hardware is configured as 4-20mA. The transducers has a 1000Ohm max load @ 24VDC. Can anyone help me figure this out? We have a 2 other (2 and 4wire) transducers connected to this CPU without any problems, the only one giving us trouble is the 3-wired. Thanks in advance. Kind regards, Jens
	Keep it simple and on-topic. A simple straight-to-the-point answer is often of more quality than a complicated one.
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8/17/2015 11:15 AM	Rate (0)
olloy Silver Member Joined: 8/27/2010 Last visit: 4/13/2024 Posts: 417 Rating: (37)	Good morning!) Can you post a drawing of how conection been made?

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8/17/2015 1:16 PM	Rate (0)
mopS04 Platinum Expert Joined: 3/5/2014 Last visit: 8/5/2022 Posts: 5521 Rating: (1054)	hi Jens, you should connect your transducer as a 4-wire-transducer. 4-wire-transducer are with a seperate power-supply, which you have with your pins "+" or "L" and "-" or "M". Where your analogue Output-Pin should connected depends on the measuring-device. Maybe you have to connect the M to the device too. SIMATIC S7-300 CPU 31xC and CPU 31x: Technical specifications see the manual on page 279 hope this helps, regards,
	FCK WAR! Be nice!
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8/18/2015 9:07 AM	Rate (0)
Jens_app Gold Member Joined: 1/5/2011 Last visit: 6/15/2024 Posts: 815 Rating: (121)	Dear All, thanks for the replies, check wiring diagram in attachment. (Sorry for duplicate posts, I have forum bugs using IE, now using firefox) Kind regards, Jens Attachment TransducerWiring.jpg (376 Downloads)
	Last edited by: Jens_app at: 8/18/2015 9:13:17 AM Keep it simple and on-topic. A simple straight-to-the-point answer is often of more quality than a complicated one.
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8/18/2015 10:20 AM	Rate (0)
mopS04 Platinum Expert Joined: 3/5/2014 Last visit: 8/5/2022 Posts: 5521 Rating: (1054)	hi Jens, thats the way it should work. regards,
	FCK WAR! Be nice!
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8/18/2015 11:15 AM	Rate (0)
Jens_app Gold Member Joined: 1/5/2011 Last visit: 6/15/2024 Posts: 815 Rating: (121)	mopS04 hi Jens, thats the way it should work. regards, Hi mopS04, thanks for the replies. I thought so too, but for some reason whenever I connect the transmitter to the input card, it drops down from 4mA to 2.6mA. I've attached a drawing which shows, what works and what doesn't work. Any ideas what could be wrong? Thanks in advance. Kind regards, Jens Attachment TransducerMultimeterWiring.jpg (293 Downloads)
	Keep it simple and on-topic. A simple straight-to-the-point answer is often of more quality than a complicated one.
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8/18/2015 11:31 AM	Rate (0)
mopS04 Platinum Expert Joined: 3/5/2014 Last visit: 8/5/2022 Posts: 5521 Rating: (1054)	hi Jens, how are your settings? Is it parametrized as 4-wire-transducer? reagards,
	FCK WAR! Be nice!
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8/18/2015 12:32 PM	Rate (0)
Jens_app Gold Member Joined: 1/5/2011 Last visit: 6/15/2024 Posts: 815 Rating: (121)	mopS04 hi Jens, how are your settings? Is it parametrized as 4-wire-transducer? reagards, Hi mopS04, Yes it is
	Keep it simple and on-topic. A simple straight-to-the-point answer is often of more quality than a complicated one.
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8/19/2015 9:36 AM	Rate (0)
Jens_app Gold Member Joined: 1/5/2011 Last visit: 6/15/2024 Posts: 815 Rating: (121)	Bump Anyone?
	Keep it simple and on-topic. A simple straight-to-the-point answer is often of more quality than a complicated one.
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8/19/2015 11:24 AM	Rate (0)
olloy Silver Member Joined: 8/27/2010 Last visit: 4/13/2024 Posts: 417 Rating: (37)	sory for late answer. please see attachment Attachment 3-wire.JPG (332 Downloads)
	Last edited by: olloy at: 8/19/2015 11:24:54 AM
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