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How do I use a PT100 sensor on AI4? (Danfoss MBT5250 - 084Z8090)

Created by: kaspergl at: 9/9/2010 10:47 AM (6 Replies)

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9/9/2010 10:47 AM	Rate (0)
kaspergl Posts: 39 Rating: (1)	Hello experts I have a S7-300 CPU313C PLC, and I want to use a PT100 sensor on the AI4 analog input. How do I setup the port? "Properties - AI5/A02 -...." under tab "Input" port 4: "Measurement type:" R-2L or RTD-2L RTD-2L says "Pt 100 std." in"Measuring range" and that seems logic, but the output value in Step7 (Monitor) is very small at 24 degrees celcius. (I use the MOVE block for my AD conversion) If I change the setup to R-2L, I get a much larger output value, and I can see it change when I heat-up the sensor.. What is the temperature range for this input?
kaspergl Posts: 39 Rating: (1)	Last edited by: kaspergl at: 9/9/2010 10:52 AM
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9/12/2010 3:03 PM	Rate (0)
Ben Rad Bronze Member Joined: 7/28/2010 Last visit: 8/31/2024 Posts: 184 Rating: (11)	Kasper, 1. You should use RTD-2L in Hardware Config for Measurement Type for the 5th AI channel. 2. Take a look at the attached file for Analog Value Representation and see if you get the right value. Regards, Behnam www.sigmaprocess.ca/blog Attachment Analog Value Representation.pdf (327 Downloads)

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9/12/2010 5:20 PM	Rate (0)
UMENCHO Diamond Member Joined: 3/21/2006 Last visit: 9/10/2024 Posts: 10228 Rating: (1181)	Hello, Perhaps this FAQ is helpful - How can you increase the resolution of temperature measurements using PT100 via the integrated analog input of the CPU 31x C? Best regards, Hristo Mihalev

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This contribution was helpful to 1 thankful Users Ton Verra

9/23/2010 11:01 AM	Rate (0)
kaspergl Posts: 39 Rating: (1)	Thanx for all you answers, but i still have some problems with my AD conversion... Mayby if I specify my test results, you mayby can tell me exactly whats wrong: PLC setup: RTD-2L - Degree celcius ----------------------------------------------------------------------------------- Fixed resistor test in port AI4 - PIW760 - (PT100 simulation): # 100 Ohm (0 degree celcius -> 0,29V) = 0x0 110 Ohm (25,7 degree celcius -> 0,31V) = 0xF0 (seems wrong) 120 Ohm (51,6 degree celcius -> 0,34V) = 0x1F0 (seems wrong) 130 Ohm (77,7 degree celcius -> 0,37V) = 0x2F0 (seems wrong) 150 Ohm (130,4 degree celcius -> 0,41V) = 0x4F0 (seems wrong) 220 Ohm (322 degree celcius -> 0,56V) = 0xC80 (seems wrong) # As an info: I only use the MOVE block to get the value - (MW20 register for the output) PLC: S7-300 CPU313C
kaspergl Posts: 39 Rating: (1)
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9/23/2010 1:29 PM	Rate (0)
Ben Rad Bronze Member Joined: 7/28/2010 Last visit: 8/31/2024 Posts: 184 Rating: (11)	Kasper, Results sound good. (0 C) = 0x0 = Decimal 0 (25,7 C = 0xF0 = Decimal 240 = 24.0 C (51,6 C) = 0x1F0 = Decimal 496 = 49.6 C (77,7 C) = 0x2F0 = Decimal 752 = 75.2 C (130,4 C) = 0x4F0= Decimal 1264 = 126.4 C (322 C) = 0xC80= Decimal 3200 = 320.0 C Regards, Behnam www.sigmaprocess.ca

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9/23/2010 2:19 PM	Rate (0)
kaspergl Posts: 39 Rating: (1)	Hello Thank you for your answer, but I hoped for at more accurately result - something like 0,1 degree celcius. Is it possible to change the resolution? Kasper
kaspergl Posts: 39 Rating: (1)
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9/23/2010 6:29 PM	Rate (0)
Ben Rad Bronze Member Joined: 7/28/2010 Last visit: 8/31/2024 Posts: 184 Rating: (11)	Kasper, Based on the Standard, the sensitivity is 0.385 ohm/°C. You are off on all values and it is kind of consistent except the last one which is way off. If theoffset is going to be consistent in the range you need, you can addor deduct the offset and get your result. There are couple of sources for error too. Check out the article in Wikipedia for RTD. http://en.wikipedia.org/wiki/Resistance_thermometer Regards, Behnam www.sigmaprocess.ca

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