Dear sir, I have SIMATIC S7-1200 and a Signal Generator Device and I use the NORM_X and SCALE-X functions in the TIA Portal program V 15 . The MIN value of NORM_X is 0.0 and the MAX is 27648.0 . It’s assumed that I use a RTD (PT100) with the Temperature Transmitter ranges ( -100 ˚C to 800 ˚C) and its output is 0-10 VDC. The output of NORM_X function is sent to two SCALE_X functions: one to scale the Ohms and the second to scale the temperature values. I depended on the RTD Temperature VS. Resistance Table to get the MIN and MAX values for these two scale functions. The first scale function which is for Ohms the MIN value is -100 ˚C whereas the MAX is 800 ˚C and the MIN value for the second scale function is 60.26 Ω and the MAX value is 375.7 Ω ( Because -100 ˚C is equal to 60.26 Ω and 800 ˚C is equal to 375.7 Ω in the reference table). But when I inject the following volt values in the Analog input of the PLC the output values of the Two SCALE_X functions are not as shown in the table?! Examples: 1- At 2.5 V the output of the first SCALE_X function is 124.4141 ˚C and the output of the second SCALE_X function is 138.91 Ω but in the Reference table when the Temperature is 124 ˚C the Ohms must be 147.58 Ω. 2- At 5 V the output of the first SCALE_X function is 349.93 ˚C and the output of the second SCALE_X function is 217.9 Ω but in the Reference table when the Temperature is 349 ˚C the Ohms must be 229.36 Ω. 3- At 7.5 V the output of the first SCALE_X function is 575.488 ˚C and the output of the second SCALE_X function is 297.0111 Ω but in the Reference table when the Temperature is 575 ˚C the Ohms must be 305.63 Ω. Why are the SCALE_X outputs not the same as what they must be as in the reference table?! And what must I do to make the outputs the same as what is shown in that table?! Thank you and I’m waiting for your reply.
Hi there, Maybe the following points help you to solve your problem: 1- If it's possible, check the temperature with another device and compare it with the calculated temperature by your program to ensure at least the calculated temperature by the PLC is correct. 2- Note that, the Norm and Scale functions can be used only for linear trends. The PT100 trend is not completely linear. I recommend using the middle range of your PT100 to write your program. for example instead of using the -100 to 800 range, use the 0 to 500 range. 3- A better way is using Analog Modules that are designed to read PT100 temperatures directly, for example, 6ES7 231-5PD30-0XB0 . 4- Please read your device's catalog and also their updated version carefully. for example, I've found this sentence inside a document about using a PT100 that has been corrected--> The SM 1231 AI 4 x 16 bit RTD did not read values correctly in the case where you powered up the CPU with no RTDs connected and later added one or more RTDs to the station
@@plcgoods Thank you for your reply. I just want to tell you that I didn’t use a real RTD or Temperature Transmitter but instead I used a signal generator to generate 0-10 V as an input to the S7-1200 built-in AI channels. For this reasons and also according to what you said the output of SCALE_X function is not the same as shown in the reference table. Best regards.
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Thanks and welcome
Dear sir,
I have SIMATIC S7-1200 and a Signal Generator Device and I use the NORM_X and SCALE-X functions in the TIA Portal program V 15 . The MIN value of NORM_X is 0.0 and the MAX is 27648.0 . It’s assumed that I use a RTD (PT100) with the Temperature Transmitter ranges ( -100 ˚C to 800 ˚C) and its output is 0-10 VDC. The output of NORM_X function is sent to two SCALE_X functions: one to scale the Ohms and the second to scale the temperature values.
I depended on the RTD Temperature VS. Resistance Table to get the MIN and MAX values for these two scale functions. The first scale function which is for Ohms the MIN value is -100 ˚C whereas the MAX is 800 ˚C and the MIN value for the second scale function is 60.26 Ω and the MAX value is 375.7 Ω ( Because -100 ˚C is equal to 60.26 Ω and 800 ˚C is equal to 375.7 Ω in the reference table).
But when I inject the following volt values in the Analog input of the PLC the output values of the Two SCALE_X functions are not as shown in the table?!
Examples:
1- At 2.5 V the output of the first SCALE_X function is 124.4141 ˚C and the output of the second SCALE_X function is 138.91 Ω but in the Reference table when the Temperature is 124 ˚C the Ohms must be 147.58 Ω.
2- At 5 V the output of the first SCALE_X function is 349.93 ˚C and the output of the second SCALE_X function is 217.9 Ω but in the Reference table when the Temperature is 349 ˚C the Ohms must be 229.36 Ω.
3- At 7.5 V the output of the first SCALE_X function is 575.488 ˚C and the output of the second SCALE_X function is 297.0111 Ω but in the Reference table when the Temperature is 575 ˚C the Ohms must be 305.63 Ω.
Why are the SCALE_X outputs not the same as what they must be as in the reference table?! And what must I do to make the outputs the same as what is shown in that table?!
Thank you and I’m waiting for your reply.
Hi there, Maybe the following points help you to solve your problem:
1- If it's possible, check the temperature with another device and compare it with the calculated temperature by your program to ensure at least the calculated temperature by the PLC is correct.
2- Note that, the Norm and Scale functions can be used only for linear trends. The PT100 trend is not completely linear. I recommend using the middle range of your PT100 to write your program. for example instead of using the -100 to 800 range, use the 0 to 500 range.
3- A better way is using Analog Modules that are designed to read PT100 temperatures directly, for example, 6ES7 231-5PD30-0XB0 .
4- Please read your device's catalog and also their updated version carefully. for example, I've found this sentence inside a document about using a PT100 that has been corrected--> The SM 1231 AI 4 x 16 bit RTD did not read values correctly in the case where you powered up the CPU with no RTDs connected and later added one or more RTDs to the station
@@plcgoods Thank you for your reply. I just want to tell you that I didn’t use a real RTD or Temperature Transmitter but instead I used a signal generator to generate 0-10 V as an input to the S7-1200 built-in AI channels. For this reasons and also according to what you said the output of SCALE_X function is not the same as shown in the reference table. Best regards.
thank you
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