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TP177 Micro + CPU224XP +PID wizard

Created by: iv73nikolov at: 10/2/2008 3:47 PM (3 Replies)

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10/2/2008 3:47 PM	Rate (0)
iv73nikolov Posts: 41 Rating: (0)	Hi, dear colleagues ! I need toenter a setpoint from the TP177Micro and control heating sistem by digital output. Temperature range is 0-400 C. The Pt100 sensor is connected to a transmitter with 0-10 V output. This signal is connected to AIW0. For the PID loop I use the wizard.No problem with the wizard and with the call of the PIDo_init.But when I enter a setpoint from the panel a "NAN" appears on the setpoint input of the PID)_init or the output was active on PV greater than SP My questions are : 1. What data type to choosein the taglistin WinCCFlexible, where is the setpoint VDxxx word? DWord or Real. I played with both... 2.Is it necessary todo something (convert, scale,..)withthe setpoint word VDxxx , before entering its value in the setpoint field of PID0_init? 3. Do I need to do something with AIW0 - scalling, normalizing...? Orit enters directlyin PID0_INIT proces value field? 4. The most general question - WNERE IS THE PROBLEM?
iv73nikolov Posts: 41 Rating: (0)	Last edited by: iv73nikolov at: 10/2/2008 3:48 PM
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10/2/2008 4:12 PM	Rate (0)
Helmut_13 Posts: 2930 Rating: (432)	Hi, basically you are right. Here the answeres to your questions: 1. The setoint for the PID is dataformat REAL. 2. If you trasfere a word from the HMI then the answere is YES because the Setpoint for the PID requires a REAL. 3. Yes in nearly all PID applications you need to scall and in lots of other applications also. 4. I have seen "NAN" in the past if the value is a REAL and in the status chart you selet a DWord. This I never had since an update to MW V4.0 SP6. Here is a link where you can download a scalling library for free: http://support.automation.siemens.com/WW/view/de/27043396 I hope this helps. Regards Helmut
Helmut_13 Posts: 2930 Rating: (432)
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10/2/2008 8:14 PM	Rate (0)
Galen Advanced Member Joined: 10/1/2008 Last visit: 2/5/2024 Posts: 21 Rating: (7)	Hi, The PID wizard will scale both the SP and PV for you. You need to make sure the scaled values match the same range. Is the Temperature range of 0-400 C, the range of the sensor or the application? If it is the range of the sensor, then 0 C with produce 0 V and 400 C will produce 10 V. If this is correct, then in the PID Wizard enter 0 as the Process Variable (PV) Low Range and 32000 as the PV High Range. Select Unipolar scaling for the Loop Input Options. How do you want the Setpoint (SP) displayed on the HMI and in your project? If you want it in degrees C then on the Loop Setpoint Scaling dialog, you should select 0.0 for the Low Range for the Loop Setpoint (SP) and 400.0 as the High Range for the Loop Setpoint. You will need to call the PID0_INIT every scan (SM0.0) from your Main. The PV_I will be the location of the analog input AIW0. The Setpoint_R will an unusedVD location that you will write to from your HMI (for example VD200). Now you can enter a Real value on your HMI between 0.0 and 400.0 degrees C for the variable VD200 and the PID input will be scaled correctly. Best Regards, Galen

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10/2/2008 8:23 PM	Rate (0)
iv73nikolov Posts: 41 Rating: (0)	Hi, Helmut! So, if I understand you right (with my stupid english) I will configure the VDxxx tag as real and transfer4 directly without conversion or scalling to PID0_INIT. Next sstep is scalling the input word AIW0 and the result is used as PV input in PID0_INIT. Third step is ...beer, beer, beer. Thank You !
iv73nikolov Posts: 41 Rating: (0)	Last edited by: iv73nikolov at: 10/2/2008 8:27 PM
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