Sensorless control circuit for heater - Page 1
Forum section: electronics / projects

author: kikerts
author_rank: Newbie
timestamp: March 05, 2014, 10:57:32 pm
content: 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.htmlhttp://www.final-yearproject.com/2009/02/hvac-thermostat.html#.UxeoEvl_u3SWhat did you can suggest?Thank you!

author: HackedFridgeMagnet
author_rank: Super Contributor
timestamp: March 05, 2014, 11:43:16 pm
content: I suggest using a temperature sensor. Why not?

author: fcb
author_rank: Super Contributor
timestamp: March 06, 2014, 09:17:44 am
content: 1. Buy a heater.2. Test heater resistance at different temperatures.3. Draw conclusions from data.

author: kikerts
author_rank: Newbie
timestamp: March 06, 2014, 09:31:32 am
content: 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.

author: fcb
author_rank: Super Contributor
timestamp: March 06, 2014, 10:35:12 am
content: 3 seconds spent searching google.http://www.tfdinc.com/transparentheaters_2_detail.htm

author: kikerts
author_rank: Newbie
timestamp: March 06, 2014, 10:44:17 am
content: Yes, I had already search this site but I don't know how to make control circuit for heater like this.

author: fcb
author_rank: Super Contributor
timestamp: March 06, 2014, 11:27:26 am
content: How much electronics knowledge do you have?

author: kikerts
author_rank: Newbie
timestamp: March 06, 2014, 01:43:36 pm
content: I am beginner in electronics.

author: NiHaoMike
author_rank: Super Contributor
timestamp: March 06, 2014, 03:25:53 pm
content: You can use an infrared thermal sensor like the TMP006.

author: delmadord
author_rank: Regular Contributor
timestamp: March 06, 2014, 03:50:11 pm
content: Quote from: NiHaoMike on March 06, 2014, 03:25:53 pmPlease, how would he solder it?

author: fcb
author_rank: Super Contributor
timestamp: March 06, 2014, 05:31:26 pm
content: Quote from: kikerts on March 06, 2014, 01:43:36 pmWhat you are attempting to do is non-trivial, I suggest you find a local EE who can help you - the voltages you are looking at make it also quite dangerous to play with also.That said, this is probably what I would do:1. Call NEUTRAL 0V for the circuit.2. Fit a current shunt resistor between NEUTRAL and one ITO heater lead.3. Fit a triac (BTA12/400 or whatever) between LIVE and the other lead.4. Drive the Triac with an opto-isolator (MOC3041, MOC3020 if you do the zero switching yourself) from a microcontroller.5. Use a potential divider on the incoming supply to feed an ADC input on the microcontroller (giving to the mains V reading)6. Feed the current shunt voltage into another input on the ADC (giving to the mains I reading).7. Use the V and I readings to calculate R, which should be mappable to temperature.8. Use R in your firmware control loop to regulate the opto-isolator duty cycle (perhaps 1Hz period).

author: kikerts
author_rank: Newbie
timestamp: March 06, 2014, 10:06:51 pm
content: Thanks for recommendation!I think I have idea how to use only analog parts:For this circuithttp://sicimatic.blogspot.com/2013/10/electronic-smart-heater-controller.htmlI can use a thermo-stable resistor between NEUTRAL and one ITO heater lead and measure the voltage across this resistor and with precision AC to DC converter(http://www.ti.com/ww/en/bobpease/assets/AN-31.pdfPage 18) filter out the DC component and give this signal to comparator, instead of LM35 temperature sensor output. What did you think about this version?

author: fcb
author_rank: Super Contributor
timestamp: March 06, 2014, 10:55:52 pm
content: It will boil-down to how accurate you need the temperature control, if you only measure current drawn by the ITO heater, your accuracy will subject to the supply voltage variation (70-100V!).You could figure out some sort of analog multiplier circuit to sort this out, but in reality it is much easier to shove it in a micro-controller.