ben frazer
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- 3/11/06
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Hi All,
Whilst I normally use a 3V 60 litre system for my house brews or splitting with mates, I wanted something a bit smaller for experimental brews and easy week night brewing. So I have gone down the recirc BIAB concept similar to others on this site, using a 40 litre electric urn and one of the little brown pumps, which returns the liquid to the middle of the mash though the top of the urn, and also to the bottom, across the element to reduce scorching risk.
The system is temperature controlled with a probe in a inserted in a 1/2" T section and is controlled by an old REX PID.
I am having two problems with this.
The first is that when I calibrate the temp probe in a bowl of water it reads perfectly (well close to) against a calibrated probe. However when I insert the probe in the T section and start recirculating the liquid, the temp probe consistently reads about 7 degrees higher than the calibrated reading. I have tried the probe in position before the pump, and also just before the return to the top of the tank. It makes no difference, the reading remains higher than the calibrated reading. Has anybody has this problem and can help with a solution?
Second problem is with my PID control. I have tried reading up on this but it is all a bit complicated for me to get my head around. Currently my PID seems to cycle the element on and off and climb its way towards the set temperature quite slowly. What I was expecting it to do was to keep the element on to move from cold to somewhere close to set point reasonably quickly, then start cycling as it got closer to the set point so as to not overshoot. Is there some thing in my PID settings that might not be right. The PID does have autotune capability, should I use this somehow?
Thanks for any help with this. I have trawled through various threads but can't find specific answers to these specific problems.
Whilst I normally use a 3V 60 litre system for my house brews or splitting with mates, I wanted something a bit smaller for experimental brews and easy week night brewing. So I have gone down the recirc BIAB concept similar to others on this site, using a 40 litre electric urn and one of the little brown pumps, which returns the liquid to the middle of the mash though the top of the urn, and also to the bottom, across the element to reduce scorching risk.
The system is temperature controlled with a probe in a inserted in a 1/2" T section and is controlled by an old REX PID.
I am having two problems with this.
The first is that when I calibrate the temp probe in a bowl of water it reads perfectly (well close to) against a calibrated probe. However when I insert the probe in the T section and start recirculating the liquid, the temp probe consistently reads about 7 degrees higher than the calibrated reading. I have tried the probe in position before the pump, and also just before the return to the top of the tank. It makes no difference, the reading remains higher than the calibrated reading. Has anybody has this problem and can help with a solution?
Second problem is with my PID control. I have tried reading up on this but it is all a bit complicated for me to get my head around. Currently my PID seems to cycle the element on and off and climb its way towards the set temperature quite slowly. What I was expecting it to do was to keep the element on to move from cold to somewhere close to set point reasonably quickly, then start cycling as it got closer to the set point so as to not overshoot. Is there some thing in my PID settings that might not be right. The PID does have autotune capability, should I use this somehow?
Thanks for any help with this. I have trawled through various threads but can't find specific answers to these specific problems.