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Connecting a pt100 via zener barrier to an Analog Input card

Created by: Jens_app at: 8/27/2013 9:34 AM (1 Replies)

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8/27/2013 9:34 AM	Rate (0)
Jens_app Gold Member Joined: 1/5/2011 Last visit: 11/29/2024 Posts: 815 Rating: (123)	Hi, I am trying to connect a 2wired Pt100 to an analog input card via azener barrier. The electrical circuit is intrinsically safe (that's why the barrier is there)and approved, so the wiring can't be changed. The zener barrier acts like a Pt100, so the output of the zener barrier is a resistance (equal to the resistance of the Pt100). The measurement type of the analog input card is set to "RT Thermal resistor (linear)" "Pt100 standard range", the measuring range module is set to "A", and the interference frequency suppresion is set to 50Hz. (the same as supply voltage frequency) But we face a problem with the readings: The analog input value is not stable, there is a lot of noise on the signal and the readings are fluctuating +-3°C, which makes the signal unusable for our application. We are trying to get a stable, correct and usable value, but we can't find the source of the problem. When connecting a Pt100 directly to the AI card, we have no problems at all. The PLC is grounded and we think everything is connected like it should be. The only thing we can think of at the moment is a conflict between the electronics of the zener barrier and the analog input card, could that be the case? If anyone faced the same problem, knows a solution or has any hints, please reply! Any suggestions are welcome. Here is some more information: -AI card is type6AG1 331-7KB02-2AB0 (SIEMENS) -Zener barrier is type 9180 ( http://www.stahl.de/fileadmin/Dateien/trennstufen/betriebsanleitungen/B9180_de_en_screen.pdf ) -Pt100 is 3 wired connected as 2wire Attachment pt100toAIviazener.jpg (193 Downloads)
	Last edited by: Jens_app at: 8/27/2013 9:37 AM *I added a sketch of the set-up 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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8/30/2013 3:43 PM	Rate (0)
Jens_app Gold Member Joined: 1/5/2011 Last visit: 11/29/2024 Posts: 815 Rating: (123)	Okay, after some contact with the suppliers, this seems to be a common problem which they couldn't explain in much detail, anyway... they suggested another analog input card.Received it today, will try it later in a few days. Just posting this,in casesomeone encounters the same problem (there is very little chance, but who knows) Gr
	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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