Classical temperature control involves monitoring a temperature sensor and adjusting the power to the heater via numerous classical methods.
I've tossed and turned at night for a week or so now trying to figure out why I haven't seen in the real world or online, why the resistance vs. temperature properties of the heating element itself is not used in a closed loop fashion to control power to said heater.
Nichrome wire for example: the resistance of the wire changes with temperature. If you characterize this aspect, why not indirectly control the temperature by varying the power such that the temperature of the wire achieves a desired resistance / temperature. The wire gets 'cool', the resistance drops, increase the duty cycle, wire gets hotter, resistance gets higher, once the resistance gets to the target, use various classical means to maintain the temperature via the resistance. The nichrome wire is in essence the RTD??? What am I missing? The advantage seems to be the elimination of a sensing device by leveraging the resistance vs temperature characteristics of the heating element itself. Ofcourse, closed loop control using the heater resistance may have it's on set of challenges. AC is typically used for these heaters. Not to mention, the heating element itself may be a huge source of noise, although I suppose this can be dealt with, it might be at an expense that far exceeds anything gained by the associated removal of the RTD.
My main interest was in reducing costs by removing the temperature sensor (e.g. RTD, thermocouple). Along with reducing system components and sources of failure. It is my experience that in industrial applications the sensing element, such as an RTD, is the common mode of failure. Eliminating the RTD would eliminate this failure mode. When a system no longer heats, there would no longer be a need to trouble shoot the RTD under the premise I've described.
In a nutshell, why can't the resistance of the heating element itself be used in a closed loop system to turn the heater on and off?
Thanks in advance,
C
I've tossed and turned at night for a week or so now trying to figure out why I haven't seen in the real world or online, why the resistance vs. temperature properties of the heating element itself is not used in a closed loop fashion to control power to said heater.
Nichrome wire for example: the resistance of the wire changes with temperature. If you characterize this aspect, why not indirectly control the temperature by varying the power such that the temperature of the wire achieves a desired resistance / temperature. The wire gets 'cool', the resistance drops, increase the duty cycle, wire gets hotter, resistance gets higher, once the resistance gets to the target, use various classical means to maintain the temperature via the resistance. The nichrome wire is in essence the RTD??? What am I missing? The advantage seems to be the elimination of a sensing device by leveraging the resistance vs temperature characteristics of the heating element itself. Ofcourse, closed loop control using the heater resistance may have it's on set of challenges. AC is typically used for these heaters. Not to mention, the heating element itself may be a huge source of noise, although I suppose this can be dealt with, it might be at an expense that far exceeds anything gained by the associated removal of the RTD.
My main interest was in reducing costs by removing the temperature sensor (e.g. RTD, thermocouple). Along with reducing system components and sources of failure. It is my experience that in industrial applications the sensing element, such as an RTD, is the common mode of failure. Eliminating the RTD would eliminate this failure mode. When a system no longer heats, there would no longer be a need to trouble shoot the RTD under the premise I've described.
In a nutshell, why can't the resistance of the heating element itself be used in a closed loop system to turn the heater on and off?
Thanks in advance,
C