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PT100 Help

Created by: alindsay at: 4/17/2009 10:35 AM (11 Replies)

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4/17/2009 10:35 AM	Rate (0)
alindsay Posts: 45 Rating: (0)	Hi All, I have wired some PT100's into an ET200M(s7-300) analog input card, I am reading the temperature ok but i dont think its 100% accurate. I want to calibrate, when i wire my certified PT100 simulator i get the following Simulator - 0.0 25.0 50.0 75.0 100.0 PLC - 0.5 25.2 50.1 74.9 100.0 I cant find any way to calibrate the analog input card and i cant find a block to enter a 10 point curve. Can anyone help me ? System is PCS7 5.2, CPU 416-3, IO is ET200M
alindsay Posts: 45 Rating: (0)
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4/19/2009 1:19 AM	Rate (0)
H-H Platinum Member Joined: 7/2/2008 Last visit: 8/26/2024 Posts: 928 Rating: (308)	Hi Alindsay, Are you sure this error in reading represents a problem for you? I don't know which module you are using. I knowthat1KF01 module has an error of+ or -1 K. I don't think other modules would have much muchless error. check your module error in S7-300 module data. I believeyour smallerror will be inmodule operational error limit. PT-100 errors appear when cable resistance is considerable specially if you are connecting PT-100 using only 2 wires. When you have considerable cable resistance, you might need to subtract cable resistance from actual reading but if you are talking about errors that lies inside module operational error limit, I don't think there's something to do. I hope someone with more experience can give you a solution.

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4/20/2009 10:22 AM	Rate (0)
alindsay Posts: 45 Rating: (0)	6ES7 331-7KF02-0AB0 Operational error limit (across temperature range, relative to input range) • Resistance thermometer Pt 100/Ni 100 ± 0. 7 % Basic error limit (operational error limit at 25 °C, relative to input range) • Resistance thermometer Pt 100/Ni 100 ± 0.5 % Temperature error (relative to input range) ± 0.005 %/K Linearity error (relative to input range) ± 0.05 % Repetition accuracy (in transient state at 25 °C, relative to input range) ± 0.05 % Temperature error of internal compensation ± 1 %
alindsay Posts: 45 Rating: (0)
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4/20/2009 11:03 AM	Rate (0)
alindsay Posts: 45 Rating: (0)	Hi H-H - This error is causing me problems. There must me a more accurate card, otherwise how am i supposed to control temperature accurately when i cannot read it accurately. I have the same error when my certified source is wired directly into the input card
alindsay Posts: 45 Rating: (0)
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4/20/2009 12:34 PM	Rate (0)
Aret Posts: 2348 Rating: (264)	Sorry, but what point is not in error limit range? Think they all are inside this limit - so it's not unproper work.... As i remedy i can sugest following - use your certified simulator to get exact values (for example every 10°C). Then using FC "POLYLINE" (i guess it's called so) you can build correction graph. Then you just add this correction to measured temperature to decrease error. Another way - use high-precision sensor and appropriate module. Another way - use 2+ sensors to get value more accurate (some math should be implemented here). Generally, these things should be taken into considiration before constructing system (all errors limits are given in catalogs and module specifications).
Aret Posts: 2348 Rating: (264)
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4/20/2009 1:52 PM	Rate (0)
alindsay Posts: 45 Rating: (0)	thanks for your suggestions Aret. Unfortunatly this is an addition to an existing system, perhaps i will replace the analog card. my problem with the error is that when i inject 25.0 degrees i want to see 25.0 in the plc, not 25.1 or any other temperature. I do have high accuraccy PT100 (10th din). I will search for an analog card with the required accuracy. I tried using the POLYG_P block, but it didnt seem to do anything for me
alindsay Posts: 45 Rating: (0)
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4/21/2009 11:58 AM	Rate (1)
Ayman Elotaify Platinum Expert Joined: 5/28/2008 Last visit: 9/9/2024 Posts: 4515 Rating: (839)	Hello, Did you thought to use PT1000 instead of PT100 for your application. PT1000 will give you higher precision and I think you can reduce the error 10 times. 10 times because, the value of the resistance at certain temp. with PT1000 =the value of the resistance at same temp. with PT100 MULTIPLIED by 10. Here's attached tables for both PT100 & PT1000 vs. temperature. With best regards, Attachment RTDs.zip (709 Downloads)
	Last edited by: Ayman Elotaify at: 4/21/2009 12:00 PM Ayman Elotaify
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4/24/2009 8:53 AM	Rate (0)
Aret Posts: 2348 Rating: (264)	Ayman, very interesting solution. Logically you are correct - if we set PT1000, error should be 1°, so actually it would be 0.1°. But i feel something strange here - guess Siemens would used this method by themselves if it would be possible. Having some doubts, because there are errors in % of range for modules also. Anyway this have to checked.
Aret Posts: 2348 Rating: (264)
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4/29/2009 3:02 PM	Rate (0)
SINAMICS_TO Bronze Member Joined: 4/24/2008 Last visit: 8/2/2024 Posts: 213 Rating: (16)	I think this FAQ will help you toqualify your measurement. http://support.automation.siemens.com/WW/view/en/26116994

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This contribution was helpful to 1 thankful Users IYYAPPAN S

4/29/2009 3:36 PM	Rate (0)
alindsay Posts: 45 Rating: (0)	Thanks for the help everyone. I have installed a head mount transmitter in the probe, so my PLC input is now 4..20 rather than RTD and i can tell you than the errors i had are now gone. When i inject 25.0 C i actually get 25.0! Andy.
alindsay Posts: 45 Rating: (0)
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This contribution was helpful to 1 thankful Users Ayman Elotaify

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