Syzygies Posted October 12, 2012 Report Share Posted October 12, 2012 So I have an old BBQ Guru Pitminder - the one that puts an oven dial on your KK, no frills. I gave away a fancier unit to a friend, the Pitminder is exactly what I want. They don't make this unit anymore, the closest match now is their flying blind NanoQ, which requires keeping track of button pushes or using an external thermometer for monitoring temps. (The KK dome thermometer is nice, but it isn't by the meat, and convergence takes a while.) Alas. Anyhow, I've experienced a number of probe failures over the years, most recently putting on a pork butt last night. (Luckily it wasn't my six butt cook last month.) I didn't notice till the KK was in the 300's, fine except I'm serving early this evening. I had a replacement probe and that did the trick. I cranked the KK way down overnight, shades of one of my favorite cooking descriptions in Legends of Texas Barbecue, where the restaurant chef let the brisket fire go out each night, to rebuild in the morning. So the Pitminder fails hot with a broken probe, blowing constantly. One can imagine trivially implementing any number of other scenarios, in digital logic here. The easiest would be to fail cold. More ambitious would be to both sound an alarm, and cycle at whatever proportions worked last time for that temperature request. The chef might not be entirely consistent on top hat position, fire construction, or outdoor temperature, but any decent guess here would be far better than the alternatives. So does anyone have experience here with how other units handle probe failure? Quote Link to comment Share on other sites More sharing options...
ThreeDJ16 Posted October 13, 2012 Report Share Posted October 13, 2012 Re: Thermocouple fails hot; which controllers fail cool? Syz, any unit with a range alarm should take care of that problem or at least alert you. A thermocouple fails open which equals basically no temperature or minimum range (0mv) and the unit reads it as low temp actuating the fan (as you stated). An RTD or thermistor would fail open giving a really high or infinite resistive reading (Ohms), equaling high temp and no fan on condition. But it could also fail shorted and be back in the same boat with fan running. Though cannot recall ever seeing one fail shorted, but one could somehow smash it into submission. Used to be that the Guru Procom read low (or out of range...can't remember now) when you broke a probe since they use thermocouples. Now through programming, they read a high number so your not stuck in a fan on constant condition. Mine reads 414 for some arbitrary reason. It also actuates the range alarm which is user programmable. I set mine for a +/- 25 since it does hold temps so well (default is +/-50). The nice thing about a Procom is having the remote sitting next to you for hearing that alarm and never having burnt butts. I know you are a minimalists here for gadget controls, but sometimes they are just worth it! -=J Quote Link to comment Share on other sites More sharing options...
Syzygies Posted October 14, 2012 Author Report Share Posted October 14, 2012 Re: Thermocouple fails hot; which controllers fail cool? Well, the butt was good enough that everyone is encouraging me to simulate the equipment failure in the future! Quote Link to comment Share on other sites More sharing options...
ThreeDJ16 Posted October 14, 2012 Report Share Posted October 14, 2012 Re: Thermocouple fails hot; which controllers fail cool? The good thing about closing down the top damper as to make the Guru fan force out air is that it limits the flow considerably. So it should never rage out of control. Would be interesting just to see the maximum temperature that could be achieved in a fan on continuous situation with damper closed down. Though it would be different depending on which fan model you purchased and slide damper setting. Just another thought on your situation. You mentioned implementing some other digital logic device, but how about a simple time delay relay (using the normally closed contacts). Could be placed on the fans current path with each pulse resetting the trigger and resetting the timer. When the pulse did not occur, then the timer would time out (say 5 minutes), the relay would then open killing the fan. Could get even more fancy and add a second timer to reset the circuit after 10 or so minutes, thus resetting the entire cycle. Nowhere near perfect, but a simple fail safe that would keep temps under some form of control. Somewhere deeply buried in the forum, is a timer I built from a kit for the Guru to achieve a lid open / fan off timer (long before they implemented that function via firmware upgrade). It was nicely configurable for about any situation. Of course it would still be simpler to buy one with built in fail safe...haha...but building is more fun. -=J Quote Link to comment Share on other sites More sharing options...
