PID control of Counters (PWM)

Question

Hello everybody!!
I work on a closed loop PID controlled problem (Labview 8.5) and I have a couple of questions in order to make some progress!
Firstly, I have to declare that my loop is composed of 2 AI channels (2 accelerometers), 1 AO channel (excitation channel-shaker), and 2 CO (for pulse creation PWM-controllers). The idea is very simple. When the AI (channel 1) value surpass or underpass a predetermined threshold value, then the appropriate CO should be activated in order to apply the necessary control forces and simultaneously to copy my data values of both AI channels in binary style for CPU velocity reasons! BUT, with the PID controller I want to optimize the Duty Cycle value of the pulses!
My questions are :
1) Why when I put Kp=Ti=Td=0 ( = run WITHOUT control) I can copy ALL the AI samples and when I start to activate the PID controller (let’s say for only Kp=0.5) I CAN’T copy ALL the AI samples? Where is my fault?
2) About the PID vi which I use, is it correct or I should use the PID vi for ARRAYS?
3) And finally, about the Boolean statement just before the Case Structures and the Shift Register, is it ok/necessary?
I attach two vis, the ReadBinar .vi is used to read my binary files generated in the end of running of the Control.vi.
Best regards
Grigorio
Attachments:
Control.vi ‏277 KB
ReadBinar.vi ‏162 KB

Answer 1

Hello Zach!
First of all, I want to thank you for your kind interest on my problem!!
I must describe you the desired process with the Control.vi. There are two AI channels writing down the acceleration of a structure in two different points (for velocity reasons I use Binary Type storage for my data). One AO channel for structure sinusoid excitation (shaker) and two CO channels for controlling two solenoid valves with which I want to control my structure acceleration (minimize it as well and fast as possible)!!
In order to help the description, let’s ‘cut’ the block diagram of Control.vi into three pieces (Before While Loop – Inside While Loop – After While Loop).
In Before While Loop section, the main question is about simultaneousness. The DAQmx Start inside the Flat Sequence Structure, do you think that is necessary, ok? I want to run my experiment for 30s and to collect 6000 samples with 200 samples/s. In addition, in the CO DAQmx timing, I have set 200 samples/channel in order to be able to change the duty cycle value because of the conditions inside the While Loop. Do you think that everything in this section works well? 
Inside the While Loop, firstly in the DAQmx Read, I have set 200 samples per Input Channel, which is also equal to the AI and AO Sampling rate! Before some days I have put there -1 and unfortunately the total written samples were less than 6000!! My main problem is how I can check all the read data without losing run velocity and simultaneous if one sample is >0 then it goes further to the first PID.vi (left solenoid valve) or if that sample is <0 then it goes further to the second PID.vi (right solenoid valve)!! When a sample has gone to a PID.vi, then I want to tune the duty cycle of the controller (PWM control) as well as possible in order to achieve the Setpoint value for the second AI channel. Are all these possible? If not, what do you suggest me?
In addition I compare the present duty cycle value with the previous one in order to be inside a tolerance value (let’s say 0.1). Moreover, is it correct the Case Structures where I want to share the positive and negative AI samples before going to the respective PID ?
Finally, After the While Loop, I believe that everything is OK. I just finish all the tasks.
I have to mention that I work on a PCI-6289 and Labview 8.5.
With best regards!
 Grigorio
Attachments:
Control.vi ‏288 KB
equal within tolerance.vi ‏9 KB
ReadBinar.vi ‏163 KB