Delta T Triggered Output Delay

[Southern Smoke]

Hello all,

This is Bill from Auburn with the Southern Smoke BBQ team in Auburn, Al.  Last year I, with a great deal of assistance from CJ, developed a temperature controller that controls two large competition Smokers.

The program works very well and the team is happy with its stability and accuracy.  It monitors some 14 temperatures and 8 voltages and currents.  The system emails me the status of the trailer power systems every hour on a 24 hour basis.With the exception of a memory leak, corrected by having the computer auto reset every afternoon at 2:30pm, the DasyLab V11/SP3 gets the job done.  Attached you will find a version of the final software.

Having used the control system, MCC 2416-AO4, for 11 competitions, we have determined there is a bit of a problem with how the controller reacts to the Smoker Door being opened while the Smoker is at temperature and under control.  As you can imagine, the Cook Chamber temperature falls off dramatically when the main door is opened.  The controller sees this and the forced air induction system is turned on to its maximum state immediately. This causes an issue in the firebox in that the Fire Box temperature rises dramatically in just a few seconds.  Normal temps in the fire box bounce around 900 degreesF but when the blowers come on while whilst the door is open the Fire Box temperatures rise to 1300-1500 degreesF in a few seconds.  Obviously these temperatures will, and already have to some extent, damage the firebox structure.

We can install some mechanical means to limit the fans if the door is open... But it requires a good bit of wiring  and rigging as the smoker was not designed for this feature.  I am seeking an program change that might accomplish the inhibition of the fan system electronically.

What I think would work is a time delay that blocks the output to the Fan Control Relay.  This delay needs to be triggered by a sudden drop in a temp sensor reading with respect to time.  For instance,  if a Cooking Chamber temp sensor dropped more than 25 degrees in less than 10 seconds then the Fan Control output would be inhibited for 300 sec AFTER the Chamber temp was within 10 degrees of the setpoint temp for that Chamber sensor. 

I have studied and worked at this issue for some time now and have not been able to design a control loop to satisfy this requirement.  If any of you folks can help I would really appreciate it.

My regards,

Bill Mixon

Head Cook

Southern Smoke BBQ Team

Auburn, Al

334-740-7927

bill.srmllc@gmail.com

[Joe_S]

Hello Bill,

Thanks for posting. While this forum isn't the main channel that customers can use for DASYLab support, you can certainly post here to see if there are users who have insight into the issue. I recommend looking into this forum post for better methods for further support. In the meantime, I'll see if I can help resolve the issue.

Let me make sure that I understand the situation. Your purpose is to create automatic temperature control for your smokers, but when you open the door, the temperature drops and you would like to create provisions for detecting these situations and handling them better.  Rather than detecting a certain amount of temperature change (which can be a variable quantity), you could try detecting when the door has been opened and configuring a trigger for that event.  Then your code can execute a specific amount of delay before starting to reheat the chamber.  Let me know what you think!

Regards,

Joe S.

[CJ_Butler__DASYLab_Pro]

Bill,

This sounds like a task for the Sample Trigger.

You'll want to play with it, but configure it to trigger when the incoming value is lower than the desired threshold, and then set it for the duration (in samples). Finally, have it trigger after the specified number of samples. 

What it should do is output a pulse when the temperature has been below the threshold for more than xx samples. You can then use that trigger pulse to turn on the fans. Because it is a pulse, you will need some subsequent logic. 

In effect, the sample trigger answers the question "has the door been open for more than x seconds? "

If the time component of the condition is not satisfied, it starts over, watching for the below threshold for xx seconds, so it automatically re-arms.