Sensorless control circuit for heater

[kikerts]

Hello!

I would like to make control circuit for heater. Heater function is to protect device from too low temperature(<0 C). My idea is to make it without temperature sensor and it sense temperature only from the heater resistance changes. The heater works with AC about 70-100V. Is it posible if resistance changes for 10 celsius amplitude only for about 10 ohms? Some variants I find in internet but in these circuit are used temperature sensors:
http://sicimatic.blogspot.com/2013/10/electronic-smart-heater-controller.html
http://www.final-yearproject.com/2009/02/hvac-thermostat.html#.UxeoEvl_u3S
What did you can suggest?
Thank you!

 

[(*steve*)]

The problem with this is that the heater will heat up when you use it so it won't then measure ambient temperature any more.

 

[kikerts]

The problem with this is that the heater will heat up when you use it so it won't then measure ambient temperature any more.

Thank you for response!
My application is to make indium tin oxide thin film heater. The reason why I don't want to use sensors is that I need to measure the actual temperature of thin film not the surround environment temperature, and if I use some sensor it also restrict visibility what is a disadvantage because I need my heater to be transparent as maximum.