security thermostat

http://www.reptiles.swelluk.com/rept...stats-555.html

there seems to be a version for everything there is a on off and a proportional.

i just read from the sites you gave me all its sais about security thermostats. i understood abiut on off and proposianal but i doesnt say about two on offs . i think its ok to put two of those?

and also what is tge difference between pulse and proposional?

pulse proportional is a type of proportional. It send a pulse of power to the heat device and then shuts down the pulse is very short duration. The heat source is not allowed to heat fully before the power is off again it changes the duration between the pulse to feather the temps. Other types act like rheostats and feather the power to the device. They both do the same thing in practice. The on/off send full power until the probe hits the user determined temp within a manufacturer determined range and then shuts off until it drops x degrees below the user input temp. Some have a narrow tolerance like 1º some are variable tolerance and it may be changed and some are wide tolerance 10 or greater degrees. They work as well but are basically averaging, you set an average temperature and it will fluctuate up and down to get it. So the pad may be fairly hot and then cool off as power is cut a proportional one the pad will be at or very very close to the temperature programmed.

Oh and the on/off may work 2 together and may not depending on how large the 'throw' (how far from the set temp it goes) of the primary one is. I have a really crummy one that was very cheap and it seems to allow a large range it would be unlikely to work well with this type of set up. A better one would work well, I have never encountered yours so it is a bit of an unknown. If you currently have only one and were thinking of buying a second I personally would recommend a proportional one and use your current one as a back up to the new one. Although if your temps are good and you see no spikes, it may be a case of 'if it ain't broke, don't fix it."

Alex

just an update on the project: i bought a thermostat with 0,5C accuracy and 2500 w output to put as a backup and then the one i have and a 20m heat cable which is proposianal by itself all this only 62 euros. im very happy!! so i think everything will work perfect! thank you for your help!!