Timing with a For Loop

[mjagani]

Thanks smercurio_fc.

Now I have a couple questions. If the difference is negative, it means the actual temperature is higher than the set point. So, wouldn't I want an output of 0 voltage?
I know that it was not a direct 1-1 relationship between voltage and temperature, but I was under the assumption that if the difference was greater than 5 degrees, the voltage output would continue being 5. However, if that is not the case, how do I change it so, say a 300-500 degree difference is 5 volts, 100-299 is 4 volts, etc.
Is there a better way to code for holding the temperature at X degrees for Y time? I don't know what else to do with it. The less than/equal to 0 thing was the only thing I could come up with for the timer to go off. If the furnace cooled and the difference became positive again, would it stop using the Case Structure part? How would I code for it so it would stay at the case structure part so even if the difference became positive, the timer could continue running and voltage would slowly be applied, allowing it to fluctuate around the target temperature.

Sorry for all the questions, I'm just really confused.

Thanks.

[smercurio_fc]

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If the difference is negative, it means the actual temperature is higher than the set point. So, wouldn't I want an output of 0 voltage?

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I have no idea, since I don't know your system's operation.

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I know that it was not a direct 1-1 relationship between voltage and temperature, but I was under the assumption that if the difference was greater than 5 degrees, the voltage output would continue being 5.

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If it's not a 1-1 relationship, then you can't code it that way. Yes, if the difference was greater than 5 degrees the coercion will force it to 5, assuming the difference is +5. If the difference is -5 then the coercion will force it to 0.

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However, if that is not the case, how do I change it so, say a 300-500 degree difference is 5 volts, 100-299 is 4 volts, etc.

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OK, this is something completely different. I'm not going to answer this until you provide a clear explanation of your system's operation because I'm not going to place myself in a position of suggesting something to someone and then having them code something that causes damage to their equipment, or worse, causes injury to someone.

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Sorry for all the questions, I'm just really confused.

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It sounds to me like your confusion has nothing to do with LabVIEW at all. It sounds to me like you don't know how to properly control instrumentation with software, or how your system operates. If you don't know how your system operates, and what your voltages control, LabVIEW isn't going to help. Perhaps you may want to consider getting some external contracting help, especially since you seem to be dealing with furnaces with temperatures in the hundreds of degrees.

[mjagani]

Well, if it helps any here's the link for the controller of the Infrared Furnace.
http://www.researchinc.com/control_930_935.asp
And this is the actual furnace.
http://www.researchinc.com/chamber_E4.asp
Here's the cooling system.
http://www.researchinc.com/coolir.asp


Message Edited by mjagani on 07-08-2008 10:47 AM

[mjagani]

I have a quick question.

What strucuture allows you to compare a number to see if it is between 2 values and returns true if it is, and false if it is not?

Thanks

[johnsold]

In Range and Coerce from the Comparisons palette.

Lynn

[smercurio_fc]

In Range and Coerce, which you're already using in your code.

[mjagani]

Won't that coerce the the value to either be the upper limit or the lower limit? I just want to know if it falls within the range.

Edit: Never mind, got it.


Message Edited by mjagani on 07-10-2008 10:32 AM

[smercurio_fc]

Have you looked at the Help file? That function has an "In Range?" output.

[mjagani]

Smercurio,
After holding X temperature for X minutes, the VI needs to cool it to a Y temperature and hold for Y minutes. I can probably figure out how to reference the temperature to a lower setpoint, but how would I cool it at a certain rate? Is it even possible to cool at a linear rate?

Thanks for all your time and help.

[smercurio_fc]

As I had mentioned earlier your VI is too simplistic to handle this process. You need to use a state machine. Going down in temperature should be no different than going up. You have a target and rate in both cases. The rate will dictate whether you can handle this using software timing or whether you need hardware timing. Most likely you can get by with software timing since temperature is not likely to change quickly unless you're dealing with a huge energy transfer.