Hello, I trying to create a program that would run a household furnace. I can't find a way to set timers for the ignitor,flame sensor and blowers. Any thoughts.

[primetime]

Hello, I'm trying to create a program that would run a household furnace. I can't find a way to set timers foe the ignitor,flame sensor and blowers. Any thoughts would be greatly appreciated. Thanks, primetime

[myle00]

You might want to look at the wait and tick count VIs. There's not much more that can be said without much more information about your project.

[SteveChandler]

Go to ni.com/training and look for the Certified LabVIEW Developer preparation materials. There are sample exams with solutions that all include timing. You can learn a lot there especially if you persue the certifications.

[smercurio_fc]

What timers? You have not indicated what hardware you're dealing with. Do you have DAQ cards? Do you have X10 devices. Your question has everything but the actual details.

[primetime]

Sorry guy's I'm new to this programming and forum stuff. Hope this info helps, If you were to study how your furnace operates  the thermostat activates calling for heat. So I need to activate the draft blower that closes the pressure switch which will activate the ignitor  for 17 seconds. then the gas valve will allow gas to the burners which activates a flame sensor that verifys that their is flame within 6 sec trial period. then the blower motor has a 45 second delay before acitvating. Once the house is up to the required temp the thermostat shuts down all switchs and valves shut off however the blower motor runs for 100 seconds longer then shuts down. and the the timers get reset.  Beings I'm new to the LabVIEW programming I've been trying to start with the sequential structure, but it doesn't seem to allow each step to happen until all the code has be sent through. Hope I didn't overwelm you with info.

[johnsold]

You need to learn about state machines.  They are designed to do the kinds of control you are talking about. There are examples which come with LV and mnay posts on this Forum about state machines.

For an actual furnace you should not try to run a control like that from a desktop OS for safety reasons.  What if the computer freezes or crashes after the gas turns on but before the flame sensor reports no flame?  The gas just keeps on flowing into the furnace.  BOOM!

If you are just trying to simulate a furnace control to learn LV, then go ahead.  Safety systems should always run on reliable hardware or on deterministic real-time operating systems.

Lynn

[primetime]

It's simulation, I've tired using the sequential case but that will not let any task perform one after the other. My lab partner has tired using case structures and got stuck trying to reset the timers. I've been trying to get information on the event structure but Haven't had much luck.

[johnsold]

In the detailed help for the event structure there is a link to caveats and recommendations for using event structures.  It is a good starting point.

It is courteous to let the Forum know when your questions are related to a school assignment or homework.  We are glad to help you learn LabVIEW, but do not do your homework for you.

You have learned the major disadvantage of the sequence structure: It must run to completion before anything else can happen.

If you are building a state machine (typically a while loop with shift registers enclosing a case structure with one case per state) and having trouble with timing, then think about your requirements. Apparently you have some time delays, but under certain conditions you must terminate a delay/wait and do something else.  One way of doing this is to have a Wait state.  The wait state has a short delay, determined by the minimum time you can delay responding to a changed condition, and a check to see if the required elapsed time has occurred.  If the time has not elapsed, the next state is the Wait state again.  The state machine can repeat any state as often as necessary.  So a 15 second delay could be implemented by going to a Wait state with a one second wait 15 times. Any error or new command will see a response in no more than one second.

Lynn

[primetime]

Thanks Lynn, it sounds like a new place to start.  What I'm looking for is different ways to get the job done. With having limited time on the training and a book thats doesn't cover alot, I thought I would learn as much or more from those that truly know the in's and out's of LabVIEW.

Dennis

[johnsold]

Dennis,

Many of us on the Forum are glad to help people learn about LV.  I know I have learned a lot from those who have more knwoledge and experience than I and from helping others.

Your approach is a good one.  You have a well defined project.  As you work through it and run into thing you do not understand, post what you have tried and ask questions that are as specific as possible to the particular problem of the moment.  Good question usually get good answers (although not always the ones you  might want).  Poor questions get littel response and that is often a request for more specific information.

Lynn