Need assistance with HM graphs...


 
PaulFisher

PaulFisher

TVWBB Super Fan
So my last few cooks have all gone the same way. For about 2-3 hours the temp is pretty stable at my set point, then something happens and it gets really wavy and never settles back in. Can anyone help? Not sure what to look for. The top vent on my WSM is about a quarter open. The min fan setting is at 0% max is 30%.

BBQ.jpg
 
Last edited:
Could be that your pit is running low on fuel (coal), and later in the cook the HM has to stoke the fire more to hit the setpoint, but then overshoots a bit, then chokes it back down, then does that over and over... Usually when your blower graph starts to show increasing magnitude like that it is running low on fuel, or you don't have enough coals burning, or ash is clogging up your airflow...
 
that pic is from today actually right now. What i've also noticed is that once the fan comes on and the temp rises, the temp will reach the set point and the fan still continues to blow at 25%. Shouldn't it shut off the fan as the temp approaches the set point? Easy to see why it's overshooting, the fan doesn't shut off even when the temps are 3-4 degrees over the set point.
 
RalphTrimble said:
Could be that your pit is running low on fuel (coal), and later in the cook the HM has to stoke the fire more to hit the setpoint, but then overshoots a bit, then chokes it back down, then does that over and over... Usually when your blower graph starts to show increasing magnitude like that it is running low on fuel, or you don't have enough coals burning, or ash is clogging up your airflow...
Click to expand...

I should have plenty of fuel, the charcoal ring was full and I'm only about 7 hours in. I just looked and there is plenty of charcoal.
 
PaulFisher said:
Shouldn't it shut off the fan as the temp approaches the set point? Easy to see why it's overshooting, the fan doesn't shut off even when the temps are 3-4 degrees over the set point.
Click to expand...
If you're logged in, hit 'p' on the keyboard to bring up the PID info popup (takes a second to come up). From there you can see exactly which PID term is running the blower. I'd guess the built-up I term is so large that it is a lot more than the D term can account for.

This would indicate on my setup that the P may be too low because the the I term is being used to get things "back on track" when it's job is just to maintain.
 
You must log in or register to reply here.

 

Back
Top