Sremac Posted August 17, 2011 Report Share Posted August 17, 2011 For some time I get complaints from my customers that my PID controlled heater loops overshoot a lot at the beginning of the operation, and then functions OK. Talking about V570. PID is connected to a physical output driving SSR thru a PWM FB. At the begining of the heating cycle PID Control Value is 100% and PWM output bit is permanently ON, of course. But later on, as the temperature rises, CV naturally starts to fall (99%, 98%, ..., 57%, ...) but PWM output bit is still permanently holding ON state, without any blinking, so my SSR is fully open, providing 100% average power to the hater, overshooting the setpoint a lot. Then, when CV becomes 0, output bit is finnaly reset, and from that moment everything is working fine - the temperature is falling, CV is rising, PWM is producing modulated pulses and the temperature is finaly under control. Also, I searched for something else that could keep output bit clamped to ON - absolutely nothing, because it occurs only two times in my program - in PWM block, and in a plain different net, driving the physical output. Also, PWM scan FB is placed in the Main Routine, so it executes all the time. This is why I added a few ladder nets that are forcing CV to zero for 0.1 second every 10 seconds during initial heating of the system, and that solves the problem, i.e. PWM output bit is pulsing immediately after CV decreases below 100%, so the regulation is fine all the time, without noticable overshoot. The question is why such a strange behaviour? (Of course, I use VisiLogic 9.3.0 with the latest OS 3.4.0) Quote Link to comment Share on other sites More sharing options...
Emil Posted August 17, 2011 Report Share Posted August 17, 2011 Please send your application or even better - simplified code to show the problem. Please send it to support@unitronics.com. We will check this problem ASAP and will take care to fix it. Quote Link to comment Share on other sites More sharing options...
Sremac Posted August 30, 2011 Author Report Share Posted August 30, 2011 Any news? Quote Link to comment Share on other sites More sharing options...
Emil Posted August 30, 2011 Report Share Posted August 30, 2011 We were able to simulate the problem here. Our R&D repaired it. We expect to issue the improvement with the comming very soon VisiLogic V9.3.1 and comming with it OS. Meantime - very simple temporary workaround - set PID output range to 998 (with 999 the problem still occure). I guess 0.2% of the power will not make any visible change in the system. Anyway - very soon te fix will be realized. Quote Link to comment Share on other sites More sharing options...
Damian Posted August 30, 2011 Report Share Posted August 30, 2011 We were able to simulate the problem here. Our R&D repaired it. We expect to issue the improvement with the comming very soon VisiLogic V9.3.1 and comming with it OS. Meantime - very simple temporary workaround - set PID output range to 998 (with 999 the problem still occure). I guess 0.2% of the power will not make any visible change in the system. Anyway - very soon te fix will be realized. Emil, It can't come soon enough. I am just finishing up a couple multizone temperature control systems that will exhibit the same issue. Would be nice not to have to submit the program with the above patch. Damian Quote Link to comment Share on other sites More sharing options...
Sremac Posted February 11, 2012 Author Report Share Posted February 11, 2012 Hay everybody! I am still waiting for the confirmation that the problem is solved. Tired of workarounds... Quote Link to comment Share on other sites More sharing options...
Emil Posted February 11, 2012 Report Share Posted February 11, 2012 It's fixed long, long time ago... Use VisiLogic V9.3.1 and OS V3.4 (25) - Update from the web. Quote Link to comment Share on other sites More sharing options...
Recommended Posts
Join the conversation
You can post now and register later. If you have an account, sign in now to post with your account.
Note: Your post will require moderator approval before it will be visible.