Hi,
Background
In the home distilling fraternity there is great division as to the suitability of PID vs SCR controls for alcohol stills, there is seldom middle ground and members get banned from forums due to heated debate.
I have both a PID (full P,I and D) and a SCR controller, in my limited experience the SCR does a better job. When distilling the liquid (wash), the wash has various volatile components with various boiling points which creates an azeotrope. The azeotrope will have a set boiling point at a specific point, but as the volatiles in the azeotrope are boiled off the boiling point alters and increases.
So the SCR lads argue that constant power is required to circumvent the ever changing boiling point which will require that the PID set point is altered on a continual basis in my opinion. The boiling point keeps rising as the volatiles are boiled off and the azeotrope becomes more water in composition. The other argument is simply that even if you set the PID to say 70C that everything with a BP below that will boil and everything with a BP above that will simply not boil. The other argument is that say 70C requires 1000W to maintain temperature, then the output will be x ml. However, if one could up the power delivery to 1500W, the BP of each component stays the same but the output ml lifts due to the increased energy.
Personal Experience
So my experience with a PID controller was exactly as above. I would constantly need to increase the set point as the azeotropes boiling point lifted. The other irritation was that the PID "pulsed" the heating element. So one could clearly hear the element get noisy as power was delivered and the stream of distillate would begin to flow, the minute power in the cycle was cut the distillate would cease to flow. The negative effect was simply that production output was severely hampered.
While with the SCR Controller I simply dial in the power required to get the distillate flowing as the rate required and I leave the controller alone for the most part.
It is not inconceivable that the P, I and D settings in my controller are awry. I did try it on factory settings, when that was not satisfactory then I tweaked it from other distilling sources.
Questions
1. Is it possible to setup a PID so that there an uninterrupted constant power delivered to the electric element?
2. If so what mode must be set, PI with no D?
3. Can one reduce the "pulsing" to effectively a continuous stream of power?
Any other insights would be most welcome.
Thanks
Background
In the home distilling fraternity there is great division as to the suitability of PID vs SCR controls for alcohol stills, there is seldom middle ground and members get banned from forums due to heated debate.
I have both a PID (full P,I and D) and a SCR controller, in my limited experience the SCR does a better job. When distilling the liquid (wash), the wash has various volatile components with various boiling points which creates an azeotrope. The azeotrope will have a set boiling point at a specific point, but as the volatiles in the azeotrope are boiled off the boiling point alters and increases.
So the SCR lads argue that constant power is required to circumvent the ever changing boiling point which will require that the PID set point is altered on a continual basis in my opinion. The boiling point keeps rising as the volatiles are boiled off and the azeotrope becomes more water in composition. The other argument is simply that even if you set the PID to say 70C that everything with a BP below that will boil and everything with a BP above that will simply not boil. The other argument is that say 70C requires 1000W to maintain temperature, then the output will be x ml. However, if one could up the power delivery to 1500W, the BP of each component stays the same but the output ml lifts due to the increased energy.
Personal Experience
So my experience with a PID controller was exactly as above. I would constantly need to increase the set point as the azeotropes boiling point lifted. The other irritation was that the PID "pulsed" the heating element. So one could clearly hear the element get noisy as power was delivered and the stream of distillate would begin to flow, the minute power in the cycle was cut the distillate would cease to flow. The negative effect was simply that production output was severely hampered.
While with the SCR Controller I simply dial in the power required to get the distillate flowing as the rate required and I leave the controller alone for the most part.
It is not inconceivable that the P, I and D settings in my controller are awry. I did try it on factory settings, when that was not satisfactory then I tweaked it from other distilling sources.
Questions
1. Is it possible to setup a PID so that there an uninterrupted constant power delivered to the electric element?
2. If so what mode must be set, PI with no D?
3. Can one reduce the "pulsing" to effectively a continuous stream of power?
Any other insights would be most welcome.
Thanks
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