PID12 - Siemens PID02 - Analog Input Scale Library and Norm_X/Scale_X in TIA Portal

[@nelsonpantaleon7751]

Hello there, sir i saw this pid at TECHNOLOGY OBJECT in tia portal project tree section whats the differentiate of this pid then pid in technology object

[@electricalautomation]

In TIA Portal, all the PID function block's instance DB come from Technology Object.

[@alearnerforsafety3692]

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.

[@electricalautomation]

I guess you are having trouble similar as the current 0 -20mA or 4-20mA OR the issue comes from your signal generator. I would recommend you validate your PLC hardware channel %IW reading when your signal generator is at 0v and 10v. replace these two values at the input of the NORM_X (they were 0.0, and 27648.0). This is a process recalibrating this ratio scaling calibration.

[@alearnerforsafety3692]

@@electricalautomation Dear sir, Thank you for your reply. I’d like to tell you that: When the signal generator is 0 V the %IW64 reading on the NORM_X input is 0 and the output of SCALE_X is 0 also. And when the signal generator is 10 V the %IW64 reading on the NORM_X input is 27645 and the output of SCALE_X is 9.998915. So, could you please advise me what I can do about this issue?

[@electricalautomation]

@@alearnerforsafety3692 Hello friend, according to your value, it looks fine. But I'd like to know that are you using the S7-1200 built-in two AI channels? If yes, your problem could be. Because these two AI channels are 10bit resolution, which is low, not very accurate. Also they are slightly sensitive from the resistance applied on the AI inputs. Also, the scaling calculation is linear math calculation, however, the RTD table is not linear. That is the reason the "RTD signal module" is needed if you need an accurate measurement. The "RTD signal module" built in the resistance table and translate the temperature via the table.

[@alearnerforsafety3692]

@@electricalautomation Thank you for your reply. I used the S7-1200 built-in two AI channels. According to your answer, I have known why the output of the SCALE_X is not the same as what is in the reference table.

[@electricalautomation]

@@alearnerforsafety3692 Glad to hear my comments would help, I think it mainly caused by the nonlinear from the temperature table. That is also the reason why it is recommended to use the RTD/TC dedicated module for temperature measurement.