11/30/2008 4:47 PM | |
Joined: 1/5/2007 Last visit: 4/7/2023 Posts: 1690 Rating: (580)
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Hi 5lamca, if i understand your question correct, then you can´t use a normal block PI-controller to solve it, because a) you have only the possibility to change your system temperature by heating, but not with cooling b) you have a big postheat if you cut off the heater --> Idon´t know, is your wonted (rated) temperature Ts every time 170 °C or have you different temperatures Ts to controll? - I used 170 °C for my example, but you can change it at a central position... --> Idon´t know what kind of sensors you wont to use - i show you the best solution for PT100 with AM2 PT100- SIEMENS-Module (look under "AM2 PT100 °C precision" for more infos). --->> At the attachmant you can find my solution, but remember that you must find out the correct parameters bei your own experiments..... The controller works with two steps: a) If the measured temperature Ta (verry) low, the heater is always ON. If Ta is going higher as a defined value (T_step1 < Ts ), the heater is going OFF AND after a waiting time (in this time the postheating effect can "work") the step 2 is aktivated... b) ...For this step 2the circuitcalculate the difference of "Ts - Ta" as base for the calculating a value interpreted as ON-time for a PWM-signal to controll the heater. This calculation can be linear or quadratic (because you have a biger postheating effect, i think that is better to get a good controlling with only a smal controlling-difference to the value Ts AND no or only a verry smal overheating). Of course you must determine and adjust all the parameters to get the best controlling results!! I have showed you an alternative to generate a PWM-signal as info. Ihope you can understand how my circuit works and modify it, if you nead. If not ask me here again... Finaly: I am working for my own mixer-controller (a 3-point-stepper-controller) to add a D-effekt (means using the changing speed of the controlling difference to calculate the ON-time) to the P-effect. This can be solved with LOGO! - but only with a complexer circuit.... ....The aktual value difference "Ts-Ta" must (cyclic) memoryed and after a defind measure time (cyclic) it must be calculated the difference between the memery-value and the new actual value. This result is then the base to calculate a value that represents the D-effect and can added to the P-effect-value (of the circuit in the attachmant). With this the controller can better respond if the aktual value Ta failed the rated value Ts...but the reaction from the controller can only be at defined time points and the used measure time should be smal for a fast controller speed and longer for a better calculation of the D-effect value.... Best regards Betel AttachmentDEMO_HeatController_V01.zip (670 Downloads) |
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12/1/2008 1:09 PM | |
Posts: 8 Rating: (0) |
Thank you betel. Your solution work's fine what conciders the overheating...the heater goes off when the temp is 160°deg (i changed the offset in B004) and then the temp. keep rising right to 170 or to 170.5 when the delay time 25s (i set it) is over. So that problem is solved. But now the problem occures with B009 and B010 (PWM)... Here i have to change parameters becouse the temp falls to let's say 160°C and then rises again to 170°C the first part of program is activated for short while....I think the problem I have is with B009 and it's calculation of ON/OFF time and the setting of max/min value of PWM and setting of periodic time. I am sending you a program that I made....In this program the temp variates between 164-172°C....Maybe you could find a connection with this program and your program to make a good one...I am having problems with the logic...I am a beginner...I will keep trying but I hope you can help me as soon as possible. The alternative pwm circuit i don't really understand how did you mean to put it into th main circuit. P.S. The wanted temp. will be sometimes higher or lower but that is not a problem...i made a counter so the wanted temp the user will be able to change with cursor key on the td. AttachmentPI and PWM.zip (510 Downloads) |
Last edited by: 5lamca at: 12/1/2008 1:17 PM |
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5/18/2012 7:03 PM | |
Posts: 29 Rating: (0) |
Hello Betel, Would you please modify your program for "CHILLING" control? Kind regards Reza
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5/18/2012 10:36 PM | |
Joined: 1/5/2007 Last visit: 4/7/2023 Posts: 1690 Rating: (580)
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Hello Reza, please we need all information about your iNPUTSIGNALS; OUTPUTSIGNALS; THE WANTED FUNKTIONS; THE VALUE ranges, units, the diyplayed values and so on... Best: your circuit with comments or a cicuit witch works nearly you want (with comments)... Best regards Betel |
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5/21/2012 6:00 PM | |
Joined: 1/5/2007 Last visit: 4/7/2023 Posts: 1690 Rating: (580)
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Hello realpower_ir, i think the circuit here ist not for your application... I will ask you some more questions here but ich think you should answer in your own article How to drive proportional valves by LOGO!
a) what is your LOGO! series ans typ (you have or you want to use)? I think it schould be a 12/24 as 0BA6 or 0BA7 b)you use a AM2 RTD-module? c) your valve need an 0 to 10 v signal to control it and it get you bach a 0 to 10 v signal as its obening status and interpreted as 0(,)0 to 100(,0) % open? d) the "wave"-reaction of your system by changing the output can have different reasens and i dont know your backround - so please controll and tell us: 1. the implementation of the sensor (contact, changing speed dT/dt, cable...) 2. external signals are added over fields (give wrong signals!) 3. what arethe PI-parameters you use? 4. the valve reactions are to big or to fast (remember your last questions to me!) 5. do you have measured or calculated the PI-parameters? 6. what ist the used temperature range and what ist the should temperature? What quality and resolutionyou want to have by regulation the temperature? Please remember LOGO!-AM2 RTD module have only 0,25 °C resolution - Perhaps it is a good idea to use an other transmitter witch can adapt its output voltage range to your needed temperatur range? With a measuring resolution of 0,1 °C may be the controller funktion is better possible... 7. Yiu should use an added temperatursensor to test the absolute minimum temperature 8then you have two informations (for safety) Best regards Betel |
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