I'm starting a project where I want to use a PID controller to hold water temperature in the ~150F range +/- 15F with as high a precision as *reasonably* possible. I know it's a bold goal but I'm shooting for .05C error. I doubt I'll get there but it should set the tone for this project.
This is the beginning stages right now and since the PID is entirely dependent on the quality of the temp input data, I'm just trying to focus on creating the best temperature sensing circuit I can. Once I'm sure I have quality input, then I'll move on with the rest of the circuit.
Like I said, I'm new but from what I've gathered from this article:
http://www.bapihvac.com/content/uploads/2010/07/RTD-vs-Thermistors.pdf
given my relatively narrow temp range, a thermistor would be the best type of temp sensor. I expect to have access to some top notch lab equipment at a medical research facility so the non-linearity of the thermistor *I think* can be resolved with proper calibration. That said, in one of the links below, it was mentioned a thermistor will be out of spec in a week if not "pre-aged".
Also I haven't decided if I should be using the on board ADC of my MCU. It's been suggested to me for the sake of my tolerances I consider a seperate ADC all together to minimize interference. Thoughts?? Suggestions for possible components?
I'll need to amplify the signal somehow. Any thoughts on the best way to do this while minimizing interference?
I came across this: http://www.ti.com/lit/ds/symlink/ina330.pdf and it appears to be a good solution in addition to reducing number of components, simplifying design and thereby cost but I'm not sure since it doesn't use a bridge circuit like most of the other examples I've found online.
Long term stability and self heating are most definitely concerns that will need to be addressed. If anyone can point me to a schematic I can reference, tips on circuit design or in general-please feel free to comment.
So far I'm referencing the threads linked below but most of the discussion seems to be about which probe to use. I'm still interested in what anyone has to say regarding probe selection but I would love to hear thoughts regarding some of my other concerns as well.
http://forum.allaboutcircuits.com/showthread.php?t=54303
http://forum.allaboutcircuits.com/showthread.php?t=35509
This is the beginning stages right now and since the PID is entirely dependent on the quality of the temp input data, I'm just trying to focus on creating the best temperature sensing circuit I can. Once I'm sure I have quality input, then I'll move on with the rest of the circuit.
Like I said, I'm new but from what I've gathered from this article:
http://www.bapihvac.com/content/uploads/2010/07/RTD-vs-Thermistors.pdf
given my relatively narrow temp range, a thermistor would be the best type of temp sensor. I expect to have access to some top notch lab equipment at a medical research facility so the non-linearity of the thermistor *I think* can be resolved with proper calibration. That said, in one of the links below, it was mentioned a thermistor will be out of spec in a week if not "pre-aged".
Also I haven't decided if I should be using the on board ADC of my MCU. It's been suggested to me for the sake of my tolerances I consider a seperate ADC all together to minimize interference. Thoughts?? Suggestions for possible components?
I'll need to amplify the signal somehow. Any thoughts on the best way to do this while minimizing interference?
I came across this: http://www.ti.com/lit/ds/symlink/ina330.pdf and it appears to be a good solution in addition to reducing number of components, simplifying design and thereby cost but I'm not sure since it doesn't use a bridge circuit like most of the other examples I've found online.
Long term stability and self heating are most definitely concerns that will need to be addressed. If anyone can point me to a schematic I can reference, tips on circuit design or in general-please feel free to comment.
So far I'm referencing the threads linked below but most of the discussion seems to be about which probe to use. I'm still interested in what anyone has to say regarding probe selection but I would love to hear thoughts regarding some of my other concerns as well.
http://forum.allaboutcircuits.com/showthread.php?t=54303
http://forum.allaboutcircuits.com/showthread.php?t=35509