PID NOT WORKING for Lower Setpoint

[kosova]

Hi everyone, 

My name is Dan and I've used this community a lot for my labview fundumentals and it is great, thanks to everyone. I no longer could find my solutionby reading other peoples questions, so my last resort was to post my problem.

I'm duing a project that requires a proportional valve (0-5V) to work with a PID. 

The project: A titlt table with angle requirements between -8 deg, 0 deg, and 8 deg. The titl for the angle will be achieved by a cylinder and my mainfeedback is an encoder. 

I'm using the PID toolkit which came with labview package. 

PID Working:

When the Setpoint is higher than the table’s current state, the PID outputs Voltage and brings the table to 8 deg and it stops. This works great...

Set Point: 8                                                       Process Variable: 0                                           PID Output: HIGH                     

PID NOT WORKING:

When the Setpoint (angleset) is lower than the tables current state the PID output voltage is 0. The difference between the setpoint and the processvariable is still 8 Deg. The table never comes down to 0 deg.

SetPoint: 0                                                    Process Variable: 8                                               PID Output: LOW

TLR: PID from the tool kit does not out voltage when the setpoint is lower than the current state of the process variable..

I'm attaching my labview code and see what you guys think that my PID problem is?

Your help is greatly appreciate it.  

[nathand]

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@kosova wrote:

PID NOT WORKING:

When the Setpoint (angleset) is lower than the tables current state the PID output voltage is 0. The difference between the setpoint and the processvariable is still 8 Deg. The table never comes down to 0 deg.

SetPoint: 0                                                    Process Variable: 8                                               PID Output: LOW

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Code looks OK.  When you write "PID Output: LOW" do you mean the output of the PID is the minimum output value?  If so, sounds like the PID loop does exactly what it's supposed to do.  Why do you have the PID output range set to +100 to -100, if the range of the valve is only 0-5?  Have you checked if you're getting an error out of the DAQmx Write when you try to write a value of -100 to a channel that's configured to accept values 0-5?  Perhaps your proportional valve needs a -5V to +5V signal?

[kosova]

Hi Nathan, 

I have a control for the PID output, that I set between 0-5V for the PID output. I think the PID toolkit in 2010 does not seem to work the way is suppost to. I have labview 2009 with the 2009 Toolkit that has worked for my other projects, so I will be installing 2009 again tonight and will see what happens. 

2) The prop.valve works between 0-5 V.

I'll let you know what happens tonight. 

Thanks for your help....

[Justin__D]

Kosova,

Were you able to run your VI correctly with 2009?

(Sorry about that Nathan)

[nathand]

Please re-read the thread, you're addressing the wrong person.