Low Power Thermal Heating

I have an interesting problem we are trying to solve. Our company uses a proprietary electrical chemical process to make measurements. These measurements become more difficult at lower temperatures. As a result, it is desired to add a heater to the chemical component to maintain a temperature of no lower then 10Degrees C. The chemical device contains highly toxic corrosive chemicals so any component placed within the device will need to be able to withstand the environment. Two thoughts are currently being considered:

1. The use of Teflon coated Ni-chrome wire as the heating element and the use of a thermal couple as the measuring means to detect the temperature of the chamber. A micro-controller would be used to determine temperature via an A/D channel and vary the power to the NiChrome heater to maintain the temperature of the chamber.

2. This option would use a surface heater and a simple I2C temperature sensor. Power would be varied to the surface heater based on the measured temperature from the temperature sensor.

My Questions are as follows:

1. What other low power/low cost heating means are available that could be used for this problem?

2. A surface heater plate would be ideal but I can't think of sources for this type of component currently. Will be doing some research but any feedback wold be helpful.

One low cost option was to use 1/2 Watt or 1 Watt low value resistors and use the simple thermal heat from these devices to heat the chamber. My thoughts are their should be a more elegant solution that is also cost efficient.

Here are a few circuit heating solutions that I have used before:

* "Hotplates on wafer probe stations":http://www.bridgetec.com/mercury.html
* "Thermostreams for heating up circuit boards":http://www.temptronic.com/Products/ThermoStream_Overview.htm
* "Heating chambers":http://www.temptronic.com/MobileTemp/MobileTemp08.htm

I have used heating resistors before and they can work really well. This "page":http://www.solorb.com/elect/constemp/ has some good information and an example heating circuit using a heating resistors.

Nice solutions...and the referenced web site was certainly useful. The key perspective is that the heater and chemical circuit/Fuel Cell are all battery powered. Ultimately we only need enough energy to raise the fuel cell from a temperature as low as -10Deg C to 5 Degree C to a constant 10 Degree C. The fulecell in question is only about 1 cubic inch in volume.....

I had a colleague that used a pcb to build heating elements. He used large serpentine traces on a printed circuit board and he was able drive enough current through the trace that it heated up, but did not damage the board. Since you only need to raise the temp by 15 degree C. That might be an option.

Another Good Idea.....Let me ponder that one....But certainly not expensive......

I designed a heater board from FR-408 some years ago. Fairly simple to do and FR-408 is good to 180 degrees C. We needed to heat up a component while in a chamber that was cooled to about -20.0 degrees C.

ref: http://www.standardpc.com/hitemp-laminates.htm

Also, I've designed a mini heat chamber using teflon pcb as the side walls with Ohmite TA series power resistors as the heating elements. This was used up to 200 degrees C for extended periods of time. The sidewalls were wrapped with rock wool and a then enclosed in a metal box. Challenging, but fun to do!

Check out heath pumps frost guard systems there may be a solution for you?