Temperature comparison, differential

[onagnan]

Solution needed, My Project Requires Temperature Differential to Indicate When a Temperature Is within 16 to 18 Degrees of Another. Within 1/2 Degree Accuracy. Temperature Range 30 Degrees Fahrenheit to 100 Degrees Fahrenheit. What Type of Comparison Circuit What I Need to Use so That I Would Be Able to Set or Have Several Alerts When Temperature Differential Is 19, 20, 21,22 or 15, 14, 13, 12 Degrees Difference. Any Help, Input, Tutoring Would Be Very Appreciative. Thank you Thomas

[russlk]

The LM335A temperature sensor sounds like what you need. The output is 10mV/deg C, which is large enough to feed directly into a limiter. The output is 5.56mV per deg F. If you know which sensor is always warmer, you need one limiter for each temperature difference that you want to sense, otherwise you need two. A bias string with taps of the temp. difference times 5.56 mV apart will do it.<p>[ December 28, 2001: Message edited by: Russ Kincaid ]</p>

[Chris Smith]

Avoid the solid state temperature sensors if you absolutely need that sort of accuracy. Their resolution isn't that accurate, claiming only a plus/minus two degree accuracy. Other than that, they work just fine. Do you want a solid state system, manual bi-metal type or both, and what sort of hysteresis do you require?

[Dean Huster]

Thomas, I designed a similar circuit and published it in the May 2001 edition of "Q & A" in Poptronics magazine. I've posted the schematic at http://167.206.219.243/forums/electroni ... s/524.html<p>This is a thermistor-based circuit designed to turn a ceiling fan on if the temperature differential between floor and ceiling went outside a set window. Since you don't seem to be worried about absolute temperature measurement, this circuit may work for you. Otherwise, you can replace the thermistor inputs with more accurate temperature sensors and use the basic comparator circuit.<p>Dean