Control three interdependent things with pid control?

I have 3 things (they are valves) that I need to control to set flows... but adjusting one of the three valves will affect how the others behave... basically they are all 4-20mA controls, but if one is moved the others will read something different.
My question, I'm having a hard time thinking about how to control these three things, I need to be able to tell any of the three to go to a certain flow regardless of where the others are... is PID the answer? If so, I need to tune them one at a time, and I don't know what to set the other 2 vlaves while I tune 1... does it matter? cause, whatever PID constants I get from tuning will be dependent on what the other 2 valves are at... or is there another way?
much thanks!

Hi Fibo,
I've linked an article you can read through for a quick intro to MIMO control.
Can I simulate MIMO models in LabVIEW?
However, I wonder if this necessarily needs a MIMO model. Regardless of how one valve affects the other, if you've got a sensor on each of your valves and implement PID separately on each one, then the relationship between the 3 valves is eliminated, is it not? We've now got 3 single-input single-output systems.
Message Edited by Tejinder G. on 03-29-2010 01:05 PM
Tejinder Gill
National Instruments
Applications Engineer
Visit ni.com/gettingstarted for step-by-step help in setting up your system.

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ssaara,
Along with the shipping examples, here is a link to the PID Control Toolkit User Manual. Fuzzy Logic control is discussed in Part II of the manual, Chapters 5 and 8 are good starting points.
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Hi all,
I have attached my program which I'm having trouble wiring up in the block diagram.... I'm fairly new to labview, but basically I have a level control project with an analog input cistern arm turning a pot for my test tank (configured as DAQ assistant voltage analog i/p) and a pump working off a reservoir (configured as DAQ assistant voltage digital o/p). My electrical side of things is working correctly and I have tested both DAQ assistants I/O's successfully off a basic program, minus the PID & PWM... I found a simple PID control subvi which I think I have wired up correctly, apart from the output variable... I also found a bit of code for PWM using the square waveform vi (far right side of the program) which I have tried to include in the program, but I've been unsuccessful with that. The ideal operation i'm looking for with this project is to be able to enter different values for the setpoint, for the PID to kick in to find that setpoint each time using the PWM to drive the pump, which has a flow rate of 13L/min. I have a manual valve to release water from my test tank which I can set accordingly.
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Attachments:
PID-RichLevelControl.vi ‏91 KB

Rich-MechatronicsStudent wrote:My questions are;
- How do I connect the 'output variable' of the PID subvi to my DAQ assistant digital output(both DAQ assistants are set at 1 sample on demand)?
I have a 'number to boolean array' function, but this gives an error saying that the number of tasks generated are not the same...
- How do I wire up the PWM bit of code? Do I need to include the 'error in & out' tabs?
-Am I on the right track with this program or am I way off the mark?!
You're a bit off track. You need the output of the PID to go into the PWM generator, and the output of the PWM to be written to the digital output. Right now you have the output of the PID connected directly to the Digital Output in a way that won't work, and the PWM generator hanging off the side not really connected to anything. Also, the PWM generator isn't really going to work since you're generating it at the same frequency as your PID loop runs. Try a simpler algorithm such as on/off control first and see if that works for your system.

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Hi everyone,
I wanna control a 12v DC motor using PID control toolkit 8.2.
- a close loop control system
- using a DAQ model: NI USB-6008
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Solved!
Go to Solution.

Well there are a lot of things you need to do this, LabVIEW software being only a part. Firstly, most DAQ cards will not source sufficient current to actually power a motor, particularly a USB6008, so you will need some form of amplifier/power driver. For closed loop you will need some feedback to tell you what the motor rotation is, usually a slotted wheel with a LED and sensor (if this is a project for school or hobby one source you might look at is an old wheeled mouse). So with these two you have a way to drive the motor and then detect its motion. Then you can get to the idea of doing PID, which is taking the feedback (from whatever sensor you end up using) scaling it to match whatever you are using, and apply it to one of the PID equations to get it to match the target value.
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Certain sites say application failed. This happens with the control panel too

When I try to get to my Skype account the screen gets an error box that says application failed.How can I stop this? Plus I can't do certain things with the control box.It won't let me do any of the listed fixes.

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Can anyone help with a PID control vi

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I am doing a project at the moment and I need to build a temperature chamber. I am using LV 7.1 and I have 4 thermistors being fedback to a daq device. I also have two heaters as part of the chamber but i want to get the thermistors readings and pid control the output to the heaters. I have the program written to get the thermistors readings and average them but im having trouble trying to think how i can pid control the heaters so i am looking for a pid vi. If anyone can help it would be great. Thanks....

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I found a lot of examples regarding the simulation of a tank - level control with PID regulator. but I still have a dilemma.
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I am having troubles with 3 things: scrolling with my laptop mouse, controlling my laptops volume with F9 and F10 keys, and I can not copy and paste images.

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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!
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I attach two vis, the ReadBinar .vi is used to read my binary files generated in the end of running of the Control.vi.
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Grigorio
Attachments:
Control.vi ‏277 KB
ReadBinar.vi ‏162 KB

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

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How can I make and wire reffercence signals(ramp,sine,square) to excite and evaluate the behaviour of the system wih PID control?

Dear all,
I am Tri, I am a beginer with LV program. Actually I used LV for my reasearch, I had tried wiht very simple thing but the problem arise because I am not familiar with LA. Why I know that problem is simple because I compare with MatLab that I had somtime used before.
I make a loop of PID control, It worked properly but I don't know how to make a refference signal to wire to the loop for excitating to evaluate the behaviour of the system. Please give me your help.
Thanks

Hi Tri,
I've employed the "simple PID.vi" without a problem, but your example is more complex. I think you use a Function generator to modulate DAQ inputs?
Perhaps someone else will be able to infer your intention and identify a flaw in the logic.
In case someone else wants to run your VI, it may help to build/attach an .llb (some sub-VIs are needed by the VI you atached.)
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2) select Development Distribution
3) Save
4) choose "New VI Library"
But first, It would be helpful to us if you clean-up the code - straighten wire-paths, minimize bends in wires, and try to avoid "tall" diagrams. Scrolling diagrams up and down is "bad form". If scrolling is necessary, left&right is preferrable!
Cheers.
(and, for the record: in my previous post, Exitation would be wired to "Process Variable", Not "Set Point" (ouch!))
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Why do I get this error when running the PID Control-Single Channel.vi: "Requested value is not a supported value for this property."

Error -200077 occurred at Property Node DAQmx Timing (arg 3) in DAQmx Timing (Sample Clock).vi:1->PID Control-Single Channel.vi
Requested value is not a supported value for this property.
Property: SampQuant.SampMode
You Have Requested: Hardware Timed Single Point
You Can Select: Finite Samples, Continuous Samples
Author: Pcorcs
Attachments:
PID Control-Single Channel.vi ‏53 KB

Actually I have already tried a few things you suggested and got as far as the DAQmx Write vi. The error at the DAQmx was a buffer error indicating i needed to set it to 2 instead of the default of 1. Tried using the DAQmx Input and Output Buffer vi to change buffer, with no luck.
Attachments:
PID Control-Single Channel.vi ‏53 KB

PID control loop slows down during execution.

Hi, I am a attaching a LV8.6 code that i am currently using to control my engine experiment. I use PID control where the input signal is an rpm value that i measure using a counter. The ttl signal from the sensor is not clean and so i use an analog trigger to generate pulses on the counter from where i measure the frequency and hence the rpm. The output is generated as an analog voltage on an output channel. The problem i am facing is that the loop runs really good when i start off but gradually the loop keeps slowing down and this greatly affects my ability to control engine speed. I am not sure why this is happening. I tried increasing the sample size and rate (so as to increase the buffer size) but this didnt have any effect on the speed. I am guessing its a problem with the way i have my loops setup.. any suggestions would be greatly appreciated.
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Attachments:
PID control loop.vi ‏33 KB

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Control three interdependent things with pid control?

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