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Hello again Thank you all for your recent help. I have certainly experienced a steep learning curve with Visilogic! I require some help with using a PID function to control the putput of one of my valves. The problem I have is that the valve is "chattering" when near to the setpoint, i.e opening and shutting very fast as the setpoint is reached. I need to slow down the operation of the output, the control does not need to be so precise - i.e control within +/- 3 mbar of the setpoint at 103 mbar, or only open again after 2 seconds of closing. I thought that I would use the PID function to sort this problem but I am really stuck. COuld anyone please help me in very simple terms, to show me how to implement the PID into my ladder? I am using MI 2 as a linearisation of a 4 to 20 mamp input ranged 0 to 1000 mbar. This is what I want to use as my process input. Set point is 103 mbar Control can be +/- 3 or 4 mbar Would like to control Output 8 with teh PID function. Thankyou in advance :)
I am using a 570 to control air temperature. I have a hot duct and cold duct in parallel with dampers 90 degrees offset on the same shaft such that when, for example, the hot duct is 100% open, the cold duct is 0% open; driven by an Oriental Motors Stepper with potentiometer positional feedback. A thermocouple provides the PV. I am using the PWM output from a V200 card to drive said stepper in a 2 wire config with one wire being enable, the other being direction. My problem is that except for the setpoint that is manually entered of course, all the parameters are zero. I know the PID won't work with zeros in all the parameter values. What are some reasons auto tune did not write the values to the table? I am running visilogic 9.5.0 I have also tried to find pre-written PID example routines and cannot find them under the help > example file. I also tried updating to no avail. In fact, when I click on examples, I get one folder that is "version 900" that has no PID example that I can find. Do example PID's exist? Also, is there any conversion that needs to take place between the PWM output and the stepper? I'm worried I'm in Unitronics "No man's land" as the folk I've talked to at Unitronics support who are consistently good about answering questions seem to have the reaction of family at the Thanksgiving table when the wayward relative pregnant with an illegitimate child is metioned. I can feel the loss of eye contact on the phone. Then when I don't see examples, it makes me wonder if Unitronics just doesn't do much with PID's? Thank you for ANY help you can offer! rookieprogrammer being baptized in fire
(Sorry for my english) Hi, I have to drive the desired temperature X. In general, the matter would be trivial, if I had one device that generates me the temperature, but unfortunately it is not. I have available: 1 - unit # 1 heating device with analog input (high power - priority 2) 2 - unit # 2 in heating mode with analog input (low power - priority 1) 3 - unit # 3 in the heating mode of the digital input (on / off - priority 3) 4 - unit # 4 in the heating mode of the digital input (on / off - priority 4) 5 - unit # 2 in the cooling mode of the analog input (with low power, but under certain operating conditions - priority 1) 6 - unit # 3 in cooling high-power digital input (on / off - priority 2) 7 - unit # 4 in cooling high-power digital input (on / off - priority 3) All these devices can be operated at the same time, of course, only in one mode. For each device there are also relationships that allow their activation. Devices do not have consistent performance - it depends on many factors, which can not measure nor even guess. I wonder on how to control these devices depending on the value of PID CV (Control Value). The only idea that comes to my mind is to assign to some range of values for the turn on of the devices. I just wonder if the PID will function OK and wonder what to do with the start and the level of "zero". If CV would -100% to 100% is rather negative control must be attached to cooling devices, and positive to heating devices. Zero disables all devices. I'm worried about controlling devices # 3 and # 4 - I can not turn on / off frequently - they are large chillers. Tonight I got the idea to control these problematic units. If the PID is saturated by X time I would turn on device #3. Where it will 2X - turn on device #3 and #4. Now I had to figure out a condition for the descent of these aggregates. I suspect also that I need to reset periodically PID saturation and add a sort of hysteresis to include these units. What do you think? Any ideas?