So then the best way to be accurate is to calibrate any "projects" with a precisely calibrated piece of lab equipment.
{snip}
Hi Rolf, you make some interesting points
however, for any given component, for the same price, surely it is prudent to use the one that is the most accurate? Using components with wide tolerances increases the risk of compounding inaccuracies. To my mind one can remove these potential inaccuracies from the project at the outset.
Accuracy and calibration are entirely different in my mind. Calibration assures that the said piece of kit is able to deliver what it claims. You can calibrate a controller of ± .01°C and you can calibrate a controller of ± 10°C. Accuracy is not determined by calibration, calibration varifies accuracy. My point is that even though the controller may not be calibrated, its accuracy can still be excellent but you just won't be able to quantify it.
I am not too sure what you mean in your point about resolution? In my experience, when one speaks of "resolving" in measurement terms it means that you are able to accurately determine to that level of detail. i.e. resolving to 0.1°C would mean that the equipment is able to accurately provide results to 0.1°C. Are you refering to the "resolution" of the display only as being different from the instruments resolution.
One important reason to use the most accurate sensor is that it improves hysteresis which is vital to being able to control within a very narrow band.
I was not knocking the virtues of thermocouples, each device has its niche and will perform well. I have used all types.
Cheers
Andrew
I am not expecting the response time to be 1ms...
I just need the circuit to be taking readings and adjusting accordingly in "realtime"
I'm not sure if Im making this too clear..
Okay.... for example.. I have a PID controller...
It takes readings once a second then adjust its PID calculations accordingly.
I need something that just has a continuous correction with out that delay
What I need is a circuit with :
-A input that reads voltage from the sensor.
-Another input to the circuit that reads voltage and is the basis for the TARGET voltage on the first input.
-Then an output that simply puts out a varying voltage depending on the differential from the sensor voltage and the set target voltage...
Is this circuit really so hard to build??...
I've searched the net a bit but cant seem to find any schematics for proportional circuits that just do those few simple things outlined in "What I need"
I've just thrown out the whole temperature topic for now until I get this circuit designed.
Are there any circuit designing/simulating programs anyone can recommend for this?
Absolute accuracy is often just a pissing contest and is never really resolved in the real working world, just a time and cash sink. What is required for good control is good repeatability.
That is unless you have a 10kw heating element mounted inside a shoe box size oven
Lefty
As long as the sensor has good repeatability then there is the possibility for good control.
Lefty
AirFLOW? That opens another can of worms, now you're dealing with fluidics and mixing. Air doesn't behave like you might think, the streams shift and stay shifted sometimes, keep that in mind.
Hope your airflow is pretty low volume, otherwise it's tough to heat, especially at 12V. If you tried to operate a little 1200W space heater at 12V it would need to pull 100 amps.
Please tell me this is a for-real project and not another damn HHO or overunity BS machine.
The project is real man... Im shocked you even asked that.
If you think I am full of it then I guess you think I am full of it.
Its not going to require a lot of air flow. A small amount. So small that I am not even worried that the heater will have a problem heating it.
I know it will work.
I have already built the trial tube that will contain the element.
Late next week I will be receiving my PWM driver kit. For the preliminary run I am going to be running it with a 75 amp mosfet.
My power supply is 12 Volts DC---- can deliver 400AMPs if necessary, so there's no lacking there. However, I suspect that I will not need much more than 20-30 amps.
After assembling the kit and hooking everything up, I am going to be testing the heating capabilities by manually adjusting the PWM driver while there is air flowing. The thermocouple will be hooked up to a meter that displays degrees Celsius so I know where I am at.
After that is tested and my theory confirmed, i will still pursue some sort of proportional control.
I hope you guys haven't given up on me yet!
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