mash tempature

[hollisbrewco]

Had my first brewday with the BCS this past Sunday and loved using the controller. I was having a little bit of trouble holding my mash temperature. I use an uninsulated 30 gallon blichmann mash tin with a false bottom. It's directly fired and I recirculate throughout the entire mash process. I have my only temperature probe placed in the return tube for the worth and I seemed to overshoot or undershoot my mash temperature by about 2 deg. I'm wondering what people with similar systems do in terms of mash temp. Probe placement. I was thinking a 6 inch probe placed in the mash itself could be a better option while leaving the probe in the return tube to make sure the wort temp. Does not exceed say 165ish deg. Another issue i had on this brewday was I was never able to hit my strike water temp exactly it kept fluctuating.
In short am I chasing temps due to my probe placment, my pid needing to be tuned or both ?

[gbrewer]

Check your settings for differential swing. Default is 4 which means 2 degrees up or 2 degrees down. Probe placement in the mash tun itself is the worst case scenario. The actually mash has various pockets of hot and cold. You could always place an additional probe in the mash kettle as you discussed to make a safety feature to shut off heat if the "mash probe" was over 165.

What do you mean by not being able to hit your strike water temperature?

[ECC]

Are you using Differential control for the Mash Tun heat output? If so, it will hold the temperature to your setpoint over the Differential Swing. So, for example, if your Swing is set to 4 and the setpoint is 152, it will hold the temperature from 150-154 (4deg swing, +- 2deg from the setpoint). If you want tighter control in Differential Control mode, tighten the swing as gbrewer pointed out.

Alternatively, PID control could give better results. I'd recommend slowing down the 'PID Sample Period'. It defaults to 3sec, which may be a bit too fast for this size of system. 6sec would be a good starting point, you may want to do a water test to get it dialed in.

[hollisbrewco]

By not hitting my strike temp I mean that my mash burner never stopped cycling but continued short bursts for the better part of an hour. I decided the temperature was good based upon the analog thermometer in the tun, I managed to come close and hit one degree over my mash temp. I am currently using pid control with a .5 deg swing. Seems like tuning my pid is the best option

[gbrewer]

Take a look at this thread and see if it helps you out.

http://www.embeddedcontrolconcepts.com/ ... 301a#p1574